VII.THYSANOPTERA.The very small black flies which are such a source of annoyance to travellers in the summer-time, and which fly into our eyes and crawl over our faces during the prevalence of warm windy weather, principally belong to a kind of insect which is characterised by having very remarkable wings when in the adult condition. These insects exist by myriads, and there are several species of them; and they are all exceedingly destructive to flowers, and especially to the bloom of cereal plants. The little black insects are to be seen on almost every flower, and they devour the delicate cellular tissues of the petals.Thrips cerealiumis very destructive when it occurs in multitudes upon the wheat, barley, and oats, for it interferes with the proper nutrition of the grain, by nibbling the protecting envelopes and the tissue which connects it to the stalk.Figs. 381, 382.—The Adult Insect and Larva of Thrips cerealium (magnified).Figs. 381, 382.—The Adult Insect and Larva ofThrips cerealium(magnified).All the members of the genusThrips—and they alone constitute the order now under consideration—possess four very narrow membranous wings, without any folds or network upon them, but furnished and decorated with beautiful fringes upon the edges. These fringescharacterise the Order, which in other respects is closely allied to the Orthoptera, and they give the name to it. The Thysanoptera ([Greek: thysanoi], fringes; [Greek: pteron], a wing) have filiform antennæ and very large eyes, and the different species of the genus Thrips have a great diversity of wing fringing. The structure of the wings is somewhat analogous to that observed in the Lepidoptera, in the Pterophorina and the Alucitina.The metamorphoses of the Thysanoptera have not received much attention, but they are known to be of the incomplete kind. The quiet chrysalis condition is not observed, and the larvæ are born from the egg greatly resembling the adults. The absence of wings is the great distinction between the larval and the imago state, as it is in the closely-allied order of the Orthoptera. The larva moults several times, and the wings are gradually added, the colour of the insect altering also.
VII.
THYSANOPTERA.
The very small black flies which are such a source of annoyance to travellers in the summer-time, and which fly into our eyes and crawl over our faces during the prevalence of warm windy weather, principally belong to a kind of insect which is characterised by having very remarkable wings when in the adult condition. These insects exist by myriads, and there are several species of them; and they are all exceedingly destructive to flowers, and especially to the bloom of cereal plants. The little black insects are to be seen on almost every flower, and they devour the delicate cellular tissues of the petals.Thrips cerealiumis very destructive when it occurs in multitudes upon the wheat, barley, and oats, for it interferes with the proper nutrition of the grain, by nibbling the protecting envelopes and the tissue which connects it to the stalk.
Figs. 381, 382.—The Adult Insect and Larva of Thrips cerealium (magnified).Figs. 381, 382.—The Adult Insect and Larva ofThrips cerealium(magnified).
All the members of the genusThrips—and they alone constitute the order now under consideration—possess four very narrow membranous wings, without any folds or network upon them, but furnished and decorated with beautiful fringes upon the edges. These fringescharacterise the Order, which in other respects is closely allied to the Orthoptera, and they give the name to it. The Thysanoptera ([Greek: thysanoi], fringes; [Greek: pteron], a wing) have filiform antennæ and very large eyes, and the different species of the genus Thrips have a great diversity of wing fringing. The structure of the wings is somewhat analogous to that observed in the Lepidoptera, in the Pterophorina and the Alucitina.
The metamorphoses of the Thysanoptera have not received much attention, but they are known to be of the incomplete kind. The quiet chrysalis condition is not observed, and the larvæ are born from the egg greatly resembling the adults. The absence of wings is the great distinction between the larval and the imago state, as it is in the closely-allied order of the Orthoptera. The larva moults several times, and the wings are gradually added, the colour of the insect altering also.
VIII.NEUROPTERA.The Neuroptera—the type of which order are theLibellulæ, or Dragon Flies—have four membranous wings, generally rather broad, provided with transverse delicately reticulated nervures, which gives them the appearance of lace. Although one of the least extensive, this Order presents the greatest modifications of form and of habits.One section of Neuroptera contains some insects which undergo incomplete metamorphoses. TheLibellulæ, theEphemeræ, and theTermites, belong to this category. The insects belonging to the other section, in which are classed thePhryganidæ,[109]or Caddis Flies, thePanorpatæ, and theMyrmelionides, or Ant Lions, undergo complete metamorphoses. The pupæ of the first walk and live absolutely in the same way as the larvæ; only, at the moment of the last transformation, the skin of the pupa splits, and the perfect insect comes forth. In the case of the second, on the contrary, the pupa is motionless, inactive, and takes no food, as in the Hymenoptera, Coleoptera, &c. In spite of this diversity in their mode of development, all these insects resemble each other too much for us to divide the Order; from which it follows that we must not attach too much importance to differences of transformation by which the insect arrives at its perfect state.The most interesting insects among the Neuroptera are theTermites, improperly called White Ants, on account of the great analogy which exists between their habits and those of ants. They constitute, by their way of living, a striking anomaly in the order in which their conformation places them. In fact, they live in very numerous societies, and build very solid and very extensive dwelling-places—quite Cyclopean or Titanic works in comparison to the tiny dimensions and weak and feeble appearance of the insect. (Plate IX.)IX.—Nests of White Ants.Many travellers have spoken of these insects. They are met with in the savannahs of North America, in Guyana, in Africa, in New Holland, and even in Europe, whither they have been imported. M. de Prefontaine relates that, when he was travelling in Guyana, he saw the negroes besieging certain strange buildings, which he calls ant-hills. They dared not attack them, except from a distance, and with fire-arms, although they had taken the precaution of digging all round them a little fosse filled with water, in which the besieged would be drowned if they made a sortie. These were the termites' nests.Perhaps it is to termites Herodotus alludes when he speaks of ants which inhabit Bactria, and which, larger than a fox, eat a pound of meat a day.[110]Retired in the sandy deserts, these gigantic insects hollow out (says he) subterranean dwellings, and raise mounds of golden sand, which the Indians carry away at the peril of their lives. Pliny, who relates the same fables, adds that there were to be seen in the Temple of Hercules the horns of these ants. Even in our own days some travellers have repeated absurd fables about termites. They have attributed to them a venom which one cannot breathe without being poisoned; they have said that a single bite was enough to cause a mortal fever. The truth, as it is revealed to us by conscientious observers, is still stranger than these fictions or errors. The termites present curious modifications, on the nature of which naturalists are not agreed. There are, in the first place, the perfect insects, males and females, which are provided with wings; then there are the neuters, which are divided intosoldiers, whose duty it is to defend the nest, and intoworkers, upon whom devolve the architectural works and household cares. These last are smaller than the soldiers. Latreille and some other naturalists think that these workers are the larvæ of the termites. Smeathman thinks that the soldiers are the pupæ. M. de Quatrefages admits that the soldiers are the neuters, and that the workers are recruited both from the larvæ and from the pupæ. It may be admitted, with other naturalists, that the soldiers and the workers are neuters: the first, abortive males; the second, abortive females. Here is, indeed, what M. Lespès has observed in the termites of the Landes. Among these insects, the most numerous are the workers: their size is that of a large ant, and their duties are to excavate galleries, to search for provisions, and to take care of the eggs, the larvæ, and the pupæ.The workers have a rounded head and short mandibles, and are blind. The soldiers, less numerous, have an enormous head—nearly as big as the rest of their body—very strong, crossed mandibles, and are blind like the workers. Anatomy showed M. Lespès that both areneuters—that is, the soldiers, males, and the workers, females—with aborted organs.The larvæ of the females much resemble the workers. Those which are to become males or females are distinguished from those which are to become neuters by very slight rudiments of wings, and their pupæ show already imperfect wings, hidden in cases; furthermore, they have eyes hidden under the skin. The males and females alone have eyes; they also have wings, which they lose immediately after the coupling. Those which proceed from the pupæ with long wing cases become small kings and queens after their swarming, which takes place at the end of May. The pupæ with short wing-cases become perfect in the month of August, and produce larger males and females, which become kings and queens. All these couples are collected by the neuters; and the queens, large and small, set to work immediately to lay. The largest are much the more fruitful. The workers do not seem to take any care of them at all. With the exception of this last peculiarity, everything probably goes on in the same manner with the exotic termites; but with the latter the queen is an object of worship.Fig. 383 represents the four types of the republic of theTermes lucifugus. On the left is a worker, on the right a soldier, in the centre a winged male, all three very much magnified, the lines drawn by their side showing the natural size. Below the male is the pregnant queen (D D D D), of a species of which we are about to speak, of the natural size.Many species of termites were studied with care by the English traveller, Smeathman, at the end of the last century, in Southern Africa. His account of them is the most exact and most complete which we have of these insects.[111]The largest of the species observed is theTermes bellicosus. The workers are a fifth of an inch long, the body soft, and of an extreme delicacy, but the sharp mandibles capable of attacking the hardest bodies. The soldiers are twice as long, and weigh as much as fifteen workers, and may be distinguished by their enormous horned head, armed with sharp pincers. The male weighs as much as thirty workers, and attains to a length of nearly four-fifths of an inch.Fig. 383.—Termes lucifugus. Male (A), Worker (B), Soldier (C), magnified. Fecundated female ofTermes bellicosus, natural size, surrounded by workers (D D D D).But the pregnant female leaves all these dimensions far behind. Her abdomen becomes two thousand times as big as the rest of herbody! She then attains to six inches in length, and weighs as much as thirty thousand workers. By a hideous contrast, the head alone does not increase in size.d d d d(Fig. 383) is an exact representation of this monster. She is always motionless and captive in her cell, entirely occupied in laying. Her fecundity surpasses all bounds: sixty eggs a minute, more than 80,000 a day. Smeathman is inclined to think that this prodigious laying goes on during the whole of the year. "This soft, whitish beast," says M. Michelet, "a belly rather than a being, is as large, at least, as one's thumb; a traveller professes to have seen one of the size of a crawfish. The larger she is, the more fruitful, the more inexhaustible, this terrible insect-mother seems to be the more adored by the fanatical rabble. She seems to be their beau ideal, their poetry, their enthusiasm. If you carry away with any rubbish a portion of their city, you see them instantly set to work at the breach to build an arch which may protect the venerated head of the mother, to reconstruct her royal cell, which will become (if there are sufficient materials) the centre, the base of the restored city. I am not astonished, though, at the excessive love which this people show for this instrument of fecundity. If all other species did not combine to destroy them, this truly prodigious mother would make them masters of the world, and—what shall I say?—its only inhabitants. The fish alone would be left; but insects would perish. It suffices to be remembered that the mother-bee does not produce in a year what the female white ant can produce in a day. By her they would be enabled to devour everything; but they are weak and tasty, and so everything devours them."[112]In fact, birds are very greedy after termites; poultry destroy immense quantities of them. Ants give chase to them and eat them by legions. The negroes in Southern Africa cannot be sated with them. They gather such as have fallen into the water, and roast them like coffee; thus prepared, they eat them by handfuls, and find them delicious. The Indians smoke the termites' nests, and catch those that have wings. They knead them up with flour, and make a sort of cake of them. Travellers, moreover, all agree in speaking of them as very nice food, comparing their flavour to that of marrow or of a sugared cream. Smeathman prefers them to the famous palm worm (ver palmisteof the colonists), a delicacy known in South America, which is the larva of theCalandra palmarum, a species of beetle. It seems, however, that an abuse of fried termites brings on a dysentery which may prove mortal.X.—Nest of the White Ant (Termes bellicosus),in Central Africa, after Smeathman.1. Male. 2, 4, 5. Neuters. 3. Gravid Female.All the species of termites are miners, but the greater number are also architects and masons. A few make their nests round a branch of a tree. This nest is of enormous dimensions: it is as large as a tun. The illustration (Plate X.)—after a drawing in Smeathman's work—shows a nest of theTermes bellicosus, composed of bits of wood firmly stuck together with gum. Above their subterranean galleries the greater part of termites construct vast edifices, which contain their magazines and nurseries. TheTermes mordaxandTermes atroxraise perfect columns, surmounted by capitals which project beyond them and give them the appearance of monstrous mushrooms. These columns attain a height of twenty inches, with a diameter of five; they are constructed with a black clay, which, worked up by the insects, acquires great hardness. The interior is hollow, or rather perforated with irregular cells; but the most curious edifices are those ofTermes bellicosus. These are irregularly conical mounds, flanked by a certain number of turrets, decreasing in height. Smeathman gives them a height of from ten to twelve feet; but Jobson[113]affirms that he has seen some as high as twenty feet. If men constructed monuments so disproportionate to their size, the great pyramid of Giseh, instead of being 146 mètres in height, would be 1,600, and would be higher than the Puy-de-Dôme!These knolls of earth are of a solidity which will bear any trial. Not only can many men mount on them without shaking them, but buffaloes establish themselves upon them as watch-towers, from which they can see over the high grass which covers the plain, if the lion or the panther is threatening them. These edifices are hollow; but their sides are from fifteen to twenty inches thick, and are as hard as a rock. They are hollowed out into galleries, which connect them with the underground dwelling. Under the dome is a pretty large vacant space, a sort of top storey or attic, occupying one-third of the total height, and which keeps up in the edifice a more uniform temperature than if all the block had been filled up. On a level with the ground is the royal cell, oblong, with a flat floor and a rounded ceiling, and pierced with round windows. All round are distributed the offices; they are rooms also with rounded and vaulted ceilings, communicating with each other by corridors. On the sides rise the magazines, with their backs placed against the walls of the house; they are filled with gums and with vegetable juices solidified and in powder. On the ceiling of the royal chamber rise pillars of abouttwo feet in height, which support the egg rooms. These are little cells with partitions of saw-dust stuck together with gum, which separate at the opening the large chambers from the clay halls. Placed between the attics and the great nave surmounting the royal hall, the nursery is in the most desirable position possible for uniformity of temperature and for ventilation.The royal cell encloses a unique couple, objects of the most assiduous attentions, but kept in closest captivity, for the doors are too narrow to afford a passage to the monstrous queen, and even to the male, who keeps generally crouching by her side. Thousands of servants busy themselves round the mother; they feed her and carry away, night and day, the myriads of eggs which she lays. The eggs are placed in the egg houses, where they give birth to white larvæ, resembling the workers, which nourish themselves at first on a sort of mouldy fungus which grows on the partitions of their cells. They then become pupæ, then neuters, or males and females, the last two being provided with wings.On a stormy evening the males and females come out of their nest by millions to couple in the air; then immediately afterwards they fall to the ground and lose their wings, when they become an easy prey to their enemies. A few couples only, picked up by the workers, are put under shelter, and become the nucleus of a new colony. The soldiers have no other occupation but to defend the nest. If man attacks them, at the first blow with the pick-axe they are to be seen running out furiously. They attack their aggressors, pierce them till they bring blood, and with their sharp pincers hang on to the wound, and allow themselves to be torn to pieces rather than leave go their hold. The negroes who have no clothes are soon put to flight; Europeans only get off with their trousers very much spotted with blood. During the combat, the soldiers strike from time to time on the ground with their pincers, and produce a little dry sound, to which the workers answer by a sort of whistling. The workers immediately make their appearance; and with their pellets of mortar set to work to stop up the holes, and to repair the damage. The soldiers then re-enter, with the exception of a small number, who remain to superintend the work of the masons; they give, at intervals, the usual signal, and the workers answer by a whistling which means, "Here we are!" as they redouble their activity. If the attack recommences, the soldiers are at their posts, defending the ground inch by inch. During this time the workers mask the passages, stop up the galleries, and wall up with care the royal cell. If you manage to penetrate as far as thissanctuary, you may pick up and carry away from the cell which contains them the precious couple without the workers in attendance on them interrupting their work, for they are blind.They never venture in sight except in extreme cases. No one is ignorant of the terrible destruction these insects occasion to the works of man. Invisible to those whom they threaten, they push on their galleries to the very walls of their houses. They perforate the floors, the beams, the wood-work, the furniture, respecting always the surface of the objects attacked in such a manner that it is impossible to be aware of their hidden ravages. They even take care to prevent the buildings they eat away from falling by filling up with mortar the parts they have hollowed out. But these precautions are only employed if the place seems suitable, and if they intend to prolong their sojourn there. In the other case they destroy the wood with inconceivable rapidity. They have been known, in one single night, to pierce the whole of a table leg from top to bottom, and then the table itself; and then, still continuing to pierce their way, to descend through the opposite leg, after having devoured the contents of a trunk placed upon the table. On account of the devastations which they occasion, Linnæus has called the white ant the greatest plague of the Indies.There exist in France two species of termites, theTermes lucifugus, a little insect of a brilliant black (at least in the male), with russety legs, which is common enough in the moors of Gascony; and the Yellow-necked White Ant (Termes flavicollis), which lives in the interior of trees and does a great deal of mischief in Spain and in the south of France to olive and other precious trees, whilst the first attacks oak and fir trees. Latreille established that it is theTermes lucifuguswhich causes such havoc at La Rochelle, at Rochefort, at Saintes, at Tournay-Charente, in the Isle of Aix, &c., where many houses have been completely undermined by these terrible insects. But M. de Quatrefages[114]has proved that the habits of the termes found in towns differ in many essential points from the habits of termes in the country. And so it is most probable that the former belong to an exotic species, which must have been unfortunately imported into France by a merchant vessel. According to M. Bobe-Moreau,[115]it was only in 1797 that termites were discovered for the first time in Rochefort, in a house which had stood for a long whileuninhabited, and which they had completely undermined. In 1804, Latreille relates, as a "hearsay," that the termites had for some years made the inhabitants of Rochefort uneasy; but in 1829 the same author tells a very different tale. He speaks with dismay of the ravages committed by this insect in the workshops belonging to the Royal Navy. The importation of the termes into France is then of recent date. A note which was sent to M. de Quatrefages by M. Beltrémieux, fixes with still greater accuracy the date of the importation of the termites; it must have taken place about 1780, a period at which the brothers Poupet, rich shipowners, caused bales of goods to come from St. Domingo to Rochefort, to La Rochelle, and to other places in that neighbourhood which possess storehouses. The ravages which the termites have committed in the towns of La Saintonge are really frightful. Like Valencia, in New Granada, these towns will find themselves one of these days suspended over catacombs. At Tournay-Charente, the floor of a dining-room fell in, and the Amphytrion and his guests tumbled together in the cellar. There may be seen in the galleries of the Museum of Natural History of Paris the wooden columns which supported this room, and which were preserved by Audouin, who had been sent on a mission to report on the damages done. Audouin also selected, as an object of curiosity, a lady's bridal veil, which had been entirely riddled with holes by the termites.At La Rochelle these insects took possession of the Prefect's house (built by the brothers Poupet), and of the Arsenal. There they invaded offices, apartments, court, and garden. They could not drive in a stake, or leave a plank in the garden, but it was attacked the next day. One fine morning the archives of the department were found destroyed, without there being the smallest trace of the damage to be seen on the exterior. The termites had mined through the wood-work, pierced the cardboard, eaten up the parchments and the papers of the administration, but had always scrupulously respected the upper leaf and edges of all the leaves. It was by mere chance that a clerk, less superficial than his colleagues, one fine day raised one of the leaves which hid thisdetritus, and thus discovered the destruction of the archives. All the papers of the Prefecture are now shut up in boxes of zinc.These termites do not venture, any more than their congeners, into the light of day. These terrible miners always envelop themselves in obscurity, and construct on all sides covered galleries as they advance into a building. M. Blanchard and M. de Quatrefages saw in La Rochelle the galleries made by them. They are tubesformed of agglutinated material, which are stuck along the walls in the cellars and the apartments, or else suspended to the roof like stalactites. Certain parts of Agen and of Bordeaux begin also to suffer from the ravages of these insects. The danger appears to be imminent.We are indebted to M. de Quatrefages for some interesting experiments on the termites of La Rochelle. Not only has the learned naturalist helped to make known to us the habits of these dark-loving insects, but he has also told us how to destroy them. Different substances have been tried in vain to stop these terrible ravages—essence of turpentine, arsenical soap, boiling lye, &c. M. de Quatrefages had recourse to gaseous injections. He tried successively binoxide of nitrogen, nitric acid, chlorine and sulphurous acid; chlorine, above all, fully answered his hopes. With pure chlorine he killed the termites instantaneously; mixed with nine-tenths of air, he suffocated them in half an hour. "For attacking the termites," says M. de Quatrefages, "one ought to choose by preference the period of their reproduction, so as to destroy the pregnant females. It is probable that, like their exotic congeners, the termites of France will endeavour to defend themselves by walling up the interior of their galleries at the first signs of an attack. The operator must then act with a great deal of promptitude, and direct the apparatus as much as possible into the very centre of their habitation, where the galleries are the broadest and the most numerous."With whatever care one acts, and whatever may be the success of a first attempt, it seems to me impossible to destroy in one campaign all the termites of a locality. In this, as in all operations of the same kind, a certain amount of perseverance is necessary, especially if it is in a town or in a country infested by them to a very great degree; in that case one will be forced to repeat the operation from time to time. When, on the contrary, the termites are already cantoned, it seems to me that the success ought to be lasting. This is fortunately the case at La Rochelle; and by knowing how to profit by it, one may doubtlessly prevent the spread of these pests, which at one time or another, may attack the whole town."[116]In 1864 the Lords of the English Admiralty addressed an inquiry to the Entomological Society of London, on the best means of preserving wood from the attacks of the Indian termites. In answer to this inquiry, the Entomological Society recommended many processes:the injection of quicklime or of creosote, the application of arsenical soap, &c. But it does not appear that these processes are infallibly efficacious, nor, above all, easy to employ.Fig. 386.—Perla marginata (larva).Fig. 384.—Larva of Perla bicaudata.Fig. 385.—Larva of a Nemoura.Fig. 386.—Perla marginata (larva).Among other Neuroptera which undergo incomplete metamorphoses, we may mention, first, the generaPerlaandNemoura,[117](Figs.384,385, and386), which flutter about the banks of rivers, and settle on stones, shrubs, and aquatic plants. Their larvæ are naked, without cases, and always live in the water, hiding themselves under stones, to watch for small insects, for they are carnivorous. One sees them often balancing their bodies, holding on to a pebble. They go through the winter, and only become pupæ in the spring. After moulting, they have the rudiments of wings. Very soon afterwards the pupæ leave the water, and undergo their metamorphosis. The adult lives only a few days, for its mouth is not suited for receiving food. The larvæ have, at the end of their bodies, two long threads, which remain in the perfectPerla, but not in the perfectNemoura; the latter lose the two caudal hairs when they arrive at the adult state. One species ofPerlais very common on the quays of Paris.Fig. 387.—Perla bicaudata.Fig. 389.—Nemoura variegata (larva).Fig. 388.—Nemoura variegata.Fig. 388.—Nemoura variegata (larva).TheEphemeridæ, or May-Fly family, have long, slender bodies,provided with two or three long silky hairs. Their name indicates the short duration of their existence. They appear in great numbers at certain seasons of the year. Their hatching takes place at sunset; they have coupled and laid their eggs by sunrise next day, and have ceased to live; so that the banks of rivers, of ponds, of lakes, are strewed with their bodies. Their number is sometimes so considerable that, according to Réaumur, the soil seems as if it were covered with snow, and they are gathered up for manure. The common Ephemera, or May-Fly (Ephemera vulgata,Fig. 390), is of a brown colour, banded with yellow, and the wings smoky, with brown spots. These insects are remarkable for their elegant flight; they are continually rising and falling. When they move their wings they rise; but if their wings, though spread out, remain motionless, as also the silky hairs which form their tail, they fall again. They may be seen in myriads in places where there is much water.Fig. 408.—Ephemera vulgata, imago.Fig. 390.Ephemera vulgata, imago.We have said that theEphemerælive only for a few hours. This is the general rule; but their existence can be prolonged for ten or fifteen days by preventing their copulation. If, however, the duration of the life of these insects is so short when they have reached the perfect state, and when the conformation of the mouth prevents them from taking any nourishment, their larvæ state is of very long continuance. Swammerdam says, in his curious Memoir, entitled "Vita Ephemeri," it is not less than three years.The females lay their eggs in one single mass, and let them fall into the water, in the form of a packet. The larvæ which come out of them are very active, and swim with great ease; but generally conceal themselves under the pebbles at the bottom. The sides of their abdomen are provided with gills, very much fringed, which serve them, not only for breathing the air under the water in the same way that fish do, but also for swimming. The larvæ have, at the extremity of their body, two or three hairs, like the perfect insect. They hollow out galleries in the beds of rivers and ponds, and live on small insects.The pupa (Fig. 392) differs only from the larva (Fig. 391) in having the rudiments of wings. When about to undergo their metamorphosis, they come out of the water and cling to plants, &c. The skin cracks on the back when it is dry, and there comes out a heavy insect, which flies feebly, and has opaque wings. It is still enveloped in a very thin skin, of which a last moult, after a few hours, frees it. This skin remains sticking to the plant on which the moulting was effected, preserving the shape of the insect. This moult is peculiar to theEphemeræ; it is the transition from the false imago (pseudo-imago) to the imago.In the same family is the genusCloëon, whose larvæ prey on minute insects. TheCloëon diptera(Fig. 393), which has only two wings, is often to be met with in houses, resting on the window panes and curtains. All these insects keep badly in collections; they lose their shape, and their members are so fragile that the least shock suffices to break them.Fig. 391.—Larva of an Ephemera.Fig. 392.—Pupa of an EphemeraTheLibellulas, or Dragon-Flies, are insects of a well-defined type.The elegance of their shape, the grace of their movements, have won for them among the French their common appellation of "Demoiselles." They are always of largish size. Many are of bright and metallic colours, which are not inferior in beauty to those of butterflies. Their wings, of an extreme delicacy, always glossy and brilliant, present varied tints; sometimes they are completely transparent, and have all the colours of the rainbow. Often, the colour of the males differs from that of the females. They may be seen fluttering about on the water during the whole summer, especially when the sun is at its highest. They fly with extreme rapidity, skimming over the water at intervals, and escaping easily when one wishes to catch them. Nothing is prettier than a troop of dragon-flies taking their sport on the side of a pond or on the banks of a river, on a fine summer's day, when a burning sun causes their wings to shine with most vivid colours.Fig. 393.—Cloëon diptera.Fig. 393.—Cloëon diptera.In the perfect state, as well as in that of the larva and the pupa, theLibellulæare carnivorous. Their rapid flight makes them expert hunters, and their enormous eyes embrace the whole horizon. They seize, while on the wing, flies and butterflies, and tear them to pieces immediately with their strong mandibles. Sometimes, the ardour of the chase leading them on far from the streams, they are met with in the fields. The female lays her eggs in the water, from which emerge larvæ which remind one somewhat of the form of the insect, only their body is more compact and their head flattened. The larvæ and pupæ inhabit the bottom of ponds and streams, where, keeping out of sight in the mud, they seek for insects, molluscs, small fish, &c. If any prey passes within their reach, they dart forward, like a spring, a very singular arm, which represents the under lip. It is a sort of animated mask, armed with strong jagged pincers and supported by strong joints, the which, taken together, is equal to the length of the body itself. This mask acts at the same time as a lipand an arm; it seizes the prey on its passage, and conveys it to the mouth. "When any aquatic insect approaches them at a time when they are in a humour for eating," says Charles de Geer, "they shoot the mask forward very suddenly and like a flash of lightning, and seize the insect between their two pincers; then, drawing back the mask, they bring the prey up to their mandibles, and begin to eat it. I have remarked that they do not spare those of their own kind, but that they eat each other up when they can, and I have also seen them devouring very small fish which I put by them. It is very difficult for other insects to avoid their blows, because, walking along generally in the water very gently, and, as it were, with measured steps—almost in the same way a cat does on the look-out for birds—they suddenly dart forward their mask and seize their prey instantaneously."[118]Fig. 394represents, to the left, the larva of the dragon-fly, with theinstrument of attack which we have called a "mask," and which it is making use of for seizing a small insect; on the right, the adult dragon-fly coming out of the nymph.Fig. 394.—Larva of the Libellula, and the perfect insect emerging.Fig. 394.—Larva of theLibellula, and the perfect insect emerging.The respiration of these larvæ is very singular. Their abdomen is terminated by appendages, which they open to allow the water to penetrate into the digestive tube, the sides of which are furnished with gills communicating with the tracheæ. The water, deprived of oxygen, is then thrown out, and the larva advances thus in the water by the recoil. It has no tufts of external lateral gills, which in the case of theEphemerædo the duty of fins. The pupa already presents stumps of wings. To effect its metamorphosis it drags itself out of the water, where it has lived for nearly a year, climbs slowly to some neighbouring plant, and hangs itself there. Very soon the sun dries and hardens its skin, which all of a sudden becomes crisp, and cracks. The dragon-fly then sets free its head and its thorax, and its legs; its wings, still soft and wanting in vigour, gain strength by coming in contact with the air, and, after a few hours, they have attained their full development. Immediately the insect abandons, like a worn-out suit, the dull slimy skin which had covered it so long, and which still preserves its shape (Fig. 394), and dashes off in quest of prey.Fig. 395.—Libellula depressa, the Common Dragon-Fly.Fig. 395.—Libellula depressa, the Common Dragon-Fly.TheLibellulasare common all over the world. Their type is theLibellula depressa(Fig. 395), very common in Europe. The male isbrown, with the abdomen blue underneath; the female, of a sort of olive-yellow, bordered by yellow on the sides. Both have the abdomen broad and flattened.TheÆshna, with a cylindrical abdomen, attains to the length of two and a half inches. Its flight is more rapid than that of the swallow. TheCalepteryxflies more slowly. The male is of a metallic blue, its diaphanous wings are traversed by a band of greenish blue; the female, of a bronzed green, has wings of a metallic green, with a yellowish mark on the edge. These insects rest on reeds, retaining their wings in a vertical position.Fig. 396.—Male Raphidia.Fig. 397.—Larva of a Raphidia.Fig. 398.—Pupa of a Raphidia.TheAgrions, which are of the same family, have the body white, brown, or green, and the eyes very prominent. They are more slim and graceful than theLibellulas, properly so called; their larva are very elongated.Fig. 399.—Mantispa pagana.In the spring, one meets in the woods with insects having large heads and elongated thoraces. The females have a long auger, with which to deposit their eggs under the bark of trees, where their larvæ, which feed on insects, and twist themselves about like small serpents, live. The pupæ are also very active; they resemble the adults very much, and have the wings laid against the body. These insects, which are met with everywhere, but always in small numbers, are theRaphidias, which we see represented (Figs.396,397,398) in the state of larva, pupa, and adult, and theMantispas(Fig. 399), one species of which is common in the south of Europe.Fig. 400.—Semblis lutarius, imago, pupa, and larva.Fig. 400.—Semblis lutarius, imago, pupa, and larva.M. Blanchard classes in the same tribe the genusSemblis, whose larvæ are aquatic, with scaly heads, provided with eyes, and with curved mandibles and short antennæ. The larvæ and the pupæ breathe, like those of theEphemeræ, by articulated external processes, or gills, analogous to those of fishes. Nevertheless the pupæ live on land, not in water. They hide themselves in the earth at the foot of trees, and the adult issues forth at the end of a fortnight, leaving its pupa skin behind. It lives but a few days. The female lays her eggs on reeds, stones, &c.Fig. 400represents the MudSemblisin its three states.Fig. 401.—Ant-lionFig. 401.—Ant-lion (Myrmeleo formicarius).We now come to those Neuroptera which undergo complete metamorphoses. They are the Myrmeleonidæ, of which the Ant-lion (Myrmeleo) is the most prominent type, and thePhryganidæ, or Caddis Flies.The larvæ of the Ant-lions live on the land, and are carnivorous. When about to undergo their transformation into pupæ, they spin forthemselves a silky cocoon. The larvæ of thePhryganeas, on the contrary, live in the water. They surround themselves with a sort of protecting case, composed of a silky shell and incrustations of all sorts. The pupæ, as well as the larvæ of these insects, breathe by means of gills.Fig. 402.—Ant-lion's funnel.Fig. 403.—Larva, cocoon, and pupa of the Ant-lion.Fig. 402.—Ant-lion's funnel.Fig. 403.—Larva, cocoon, and pupa of the Ant-lion.The Ant-lion (Myrmeleo formicarius,Fig. 401) is found in the environs of Paris. It is an elegant insect, resembling the dragon-fly, but is distinguished from it by its antennæ. Its larva is of a rosy, rather dirty grey, with little tufts of blackish hair on its very voluminous abdomen. Its legs are rather long and slender; the two anterior pair of legs are directed forwards, whilst the hind legs are fixed against the body, and only permit the animal to walk backwards. These larvæ are met with in great abundance in sandy places very much exposed to the heat of the sun. There they construct for themselves a sort of funnel in the sand (Fig. 402), by describing, backwards, the turns of a spiral whose diameter gradually diminishes. Their strong square head serves them as a spade with which to throw the sand far away: they then hide themselves at the bottom of the hole, their head alone being out, and wait with patience for some insect to come near. Scarcely has the ant-lion perceived its victim on the borders of its funnel, when it throws at it a shower of dust to alarm it, and make it fall to the bottom of the precipice, which does not fail to happen. Then it seizes it with its sharp mandibles, andsucks its blood; after which it throws its empty skin out of the hole and resumes the look-out. Ants especially become its prey, whence its name of Ant-lion. Towards the month of July, the larvæ make themselves a spherical cocoon, mixed with grains of sand, in which they are transformed into pupæ which are hatched towards the end of August. The perfect ant-lions diffuse an odour of roses; their flight, which is weak, distinguishes them from the dragon-flies. We meet in the south of France with a very beautiful species of Ant-lion, theMyrmeleo libelluloides(Fig. 404); its larva can move forwards, and does not dig itself a funnel.Fig. 404.—Myrmeleo libelluloides.The genusAscalaphus(Fig. 407) is remarkable for the long clubbed antennæ of its members, and for their rapid flight. They like the sun, and live especially in hot countries; however, one meets with theAscalaphus, in the month of July, near Paris, on the dry declivities of Lardy and of Poquency. Their larvæ (Fig. 406) have mandibles adapted for suction. They watch for insects under heaps of stones, and spring upon their prey.Fig. 405.—Larva of Myrmeleo libelluloides.Fig. 406.—Larva of Ascalaphus.Fig. 407.—Ascalaphus meridionalis.The first states of theNemoptera[119](Fig. 408) are as yet little known. They are insects with wings spotted with yellow and black, the lower ones almost linear, and are met with in southern countries, and but very rarely in the south of France.TheHemerobii, to which are given by the French the name ofDemoiselles terrestres, or Land Dragon-Flies, are very small delicate insects, of an apple-green colour, with golden red eyes. These insects leave on the fingers, when seized, an offensive odour. Réaumur calls themLions des pucerons(Plant-Lice Lions), because their larvæ, which resembles the larvæ of the ant-lions, and which live on plants, feed onplant-lice. They attack also caterpillars. Their mandibles are provided with a canal for suction, like those of the foregoing species.Fig. 408.—Nemoptera Coa.Fig. 409.—Osmylus maculatus.The insects of the genusOsmylus(Fig. 409) are rather rare; but may be found in the shrubs which border ponds. They also belong to theHemerobidæ. Their larvæ live in wet ground.Fig. 410.—Panorpa, male and female.Fig. 410.—Panorpa, male and female.ThePanorpatæconstitute a singular little family, having a peculiar shaped head, which is prolonged to a sort of long and slender beak. Aristotle called them Scorpion Flies, and thought they were winged scorpions. ThePanorpas, properly so called (Fig. 410), are found on hedges and plants during the summer.They have slim bodies spotted with yellow and black, and four straight wings, also spotted with black. In the males the abdomen terminates in a pair of pincers (Fig. 411), which rather remind one of the tail of a scorpion, and which are destined to seize their prey, which they kill by piercing with their beak. The female lays her eggs in the ground (Fig. 412). In a week the larva makes its appearance; it is a month in developing, it then buries itself still deeper in the earth, and changes into a pupa, which, after a fortnight, comes again into the light in the form of a perfect insect. There are two other genera ofPanorpatæ, of whichBittacus tipularis(Fig. 413), resembling a large gnat, furnished with four wings, andBoreus hyemalis(Fig. 414), of a brilliant black, met with in Sweden and in the elevated parts of the Alps, jumping about on the snow in considerable troops—are representatives. The latter has been found in England.Fig. 411.—Pincer of male Panorpa.Fig. 412.—Female Panorpa laying.Fig. 414.—Boreus hyemalis (magnified and natural size).Fig. 413.—Bittacus tipularis.Fig. 414.—Boreus hyemalis (magnified and natural size).Fig. 415.—Larva of Phryganea rhombica.Fig. 416.—Phryganea rhombica, in repose.Fig. 416.—Phryganea rhombica, in repose.Fig. 417.—Phryganea rhombica.Fig. 415.—Larva of Phryganea rhombica.Fig. 417.—Phryganea rhombica.ThePhryganidæ, or Caddis Flies, are known by their larvæ, of which anglers make great use. Réaumur classed them as aquatic moths. The soft and delicate body of the larvæ is protected by a case, to which they cling by two hooks, placed at the extremity of their abdomen. They are called by different names in allusion to their habits; as, for instance, case worms, from their living in a case covered with little bits of wood or sand, which they draw after them as they go. Their scientific name,Phryganea, signifiesfagot.[120]ThePhryganeæ, in the adult state, very much resemble moths. They approach them in having rudimentary mouths, and wings without articulations, but furnished with small hairs, analogous to the scales of Lepidoptera. They may be said to form a sort of connection between the Lepidoptera and Neuroptera. They have been calledMouches papilionacées, or Papilionaceous Flies. The eggs laid by the femalePhryganeaare enclosed in gelatinous capsules, which swell in the water and attach themselves to stones, &c. The larva has the appearance of a little worm without feet. It is soon hatched, and resembles at first a little black line, and may be easily reared in an aquarium. The operation of making the silky case which it draws after it, and which protects its abdomen, may then be observed. When it is disturbed, it retreats entirely within its case. The interior is smooth, and lined with mud; on the exterior it is fortified with stones, &c.Fig. 418.Regular cases of a Phryganea.ThePhryganea rhombica(Figs.415,416,417) furnishes its case with bits of wood or grass, arranged as shown inFig. 418. Some species arrange these bits of wood and glass in spiral, others in parallel series. ThePhryganea flavicorniscovers its dwelling with little shells. "These kinds of dress," says Réaumur, "are very pretty, but they are also excessively singular. A savage who, instead of being covered with furs, should be covered with musk rats, moles, or other entire animals, would have on an extraordinary costume; this is in some sort the case with our larvæ." OtherPhryganeæemploy for constructing the case which serves them as a dwelling sand and small pebbles; each species always employing the same materials, unless they are entirely deprived of these and obliged to employ others. These cases protect the larvæ against the voracity of their enemies. The larvæ have a scaly head; and the three first rings of their body are harder than the rest. They live in water, and breathe by means of branchious sacs, arranged on the abdomen in soft and flexible tufts. They eat everything that is presented to them: leaves, and even insects and the larvæ of their own kind. The pupæ are motionless. They stay about a fortnight in their case, the orifice of which is closed by gratings of silk, then break through the gratings, and leave their prison. In this state (Fig. 419) they swim on the water until they meet with an object to which they can attach themselves, and so get out. Then they swell till they crack their skin over the back, and the perfect insect emerges.ThePhryganea pilosa(Fig. 420) is of a yellowish grey, with hairy wings, little adapted for flying. These insects do not eat, and never leave the neighbourhood of the water. During the day they rest on flowers, on walls, or on the trunks of trees, their wings folded back, and their antennæ together. In the evening they fly in dense swarms over streams and ponds. They are attracted by light, as are many nocturnal insects; and are sometimes found in great numbers on the lamps on the quays in Paris.Fig. 419.—Pupa of Phryganea pilosa, magnified.Fig. 420.—Phryganea pilosa.Fig. 419.—Pupa of Phryganea pilosa, magnified.Fig. 420.—Phryganea pilosa.TheHydropsyches(Fig. 421) andRhyacophili(Fig. 422) are small insects which resemble thePhryganeævery closely. Their larvæ have, for the purposes of respiration, some gills, others retractile tubes. They construct for themselves fixed places of shelter, more or less imperfect, at the bottom of the water, and against large stones,which they leave occasionally for a few moments. Sometimes these cases contain several larvæ.Fig. 421represents the various states of aHydropsyche; the larva is seen on the left, the pupa on the right, the winged insect in the middle. Two of the insect's tents, or places of shelter, are represented below.Fig. 422shows the different states ofRhyacophilus vulgatus, larva, cocoon, pupa, and imago. The genusRhyacophilushas this peculiarity, that the larva spins itself a cocoon in the interior of its dwelling before changing into a pupa.Fig. 421.—Hydropsyche (Phryganea) atomaria, larva, pupa, imago, and larva-case.Fig. 421.—Hydropsyche (Phryganea) atomaria, larva, pupa, imago, and larva-case.Fig. 422.—Rhyacophilus vulgatus, larva, pupa, cocoon, and imago (male).Fig. 422.—Rhyacophilus vulgatus, larva, pupa, cocoon, and imago (male).
VIII.
NEUROPTERA.
The Neuroptera—the type of which order are theLibellulæ, or Dragon Flies—have four membranous wings, generally rather broad, provided with transverse delicately reticulated nervures, which gives them the appearance of lace. Although one of the least extensive, this Order presents the greatest modifications of form and of habits.
One section of Neuroptera contains some insects which undergo incomplete metamorphoses. TheLibellulæ, theEphemeræ, and theTermites, belong to this category. The insects belonging to the other section, in which are classed thePhryganidæ,[109]or Caddis Flies, thePanorpatæ, and theMyrmelionides, or Ant Lions, undergo complete metamorphoses. The pupæ of the first walk and live absolutely in the same way as the larvæ; only, at the moment of the last transformation, the skin of the pupa splits, and the perfect insect comes forth. In the case of the second, on the contrary, the pupa is motionless, inactive, and takes no food, as in the Hymenoptera, Coleoptera, &c. In spite of this diversity in their mode of development, all these insects resemble each other too much for us to divide the Order; from which it follows that we must not attach too much importance to differences of transformation by which the insect arrives at its perfect state.
The most interesting insects among the Neuroptera are theTermites, improperly called White Ants, on account of the great analogy which exists between their habits and those of ants. They constitute, by their way of living, a striking anomaly in the order in which their conformation places them. In fact, they live in very numerous societies, and build very solid and very extensive dwelling-places—quite Cyclopean or Titanic works in comparison to the tiny dimensions and weak and feeble appearance of the insect. (Plate IX.)
IX.—Nests of White Ants.
Many travellers have spoken of these insects. They are met with in the savannahs of North America, in Guyana, in Africa, in New Holland, and even in Europe, whither they have been imported. M. de Prefontaine relates that, when he was travelling in Guyana, he saw the negroes besieging certain strange buildings, which he calls ant-hills. They dared not attack them, except from a distance, and with fire-arms, although they had taken the precaution of digging all round them a little fosse filled with water, in which the besieged would be drowned if they made a sortie. These were the termites' nests.
Perhaps it is to termites Herodotus alludes when he speaks of ants which inhabit Bactria, and which, larger than a fox, eat a pound of meat a day.[110]Retired in the sandy deserts, these gigantic insects hollow out (says he) subterranean dwellings, and raise mounds of golden sand, which the Indians carry away at the peril of their lives. Pliny, who relates the same fables, adds that there were to be seen in the Temple of Hercules the horns of these ants. Even in our own days some travellers have repeated absurd fables about termites. They have attributed to them a venom which one cannot breathe without being poisoned; they have said that a single bite was enough to cause a mortal fever. The truth, as it is revealed to us by conscientious observers, is still stranger than these fictions or errors. The termites present curious modifications, on the nature of which naturalists are not agreed. There are, in the first place, the perfect insects, males and females, which are provided with wings; then there are the neuters, which are divided intosoldiers, whose duty it is to defend the nest, and intoworkers, upon whom devolve the architectural works and household cares. These last are smaller than the soldiers. Latreille and some other naturalists think that these workers are the larvæ of the termites. Smeathman thinks that the soldiers are the pupæ. M. de Quatrefages admits that the soldiers are the neuters, and that the workers are recruited both from the larvæ and from the pupæ. It may be admitted, with other naturalists, that the soldiers and the workers are neuters: the first, abortive males; the second, abortive females. Here is, indeed, what M. Lespès has observed in the termites of the Landes. Among these insects, the most numerous are the workers: their size is that of a large ant, and their duties are to excavate galleries, to search for provisions, and to take care of the eggs, the larvæ, and the pupæ.The workers have a rounded head and short mandibles, and are blind. The soldiers, less numerous, have an enormous head—nearly as big as the rest of their body—very strong, crossed mandibles, and are blind like the workers. Anatomy showed M. Lespès that both areneuters—that is, the soldiers, males, and the workers, females—with aborted organs.
The larvæ of the females much resemble the workers. Those which are to become males or females are distinguished from those which are to become neuters by very slight rudiments of wings, and their pupæ show already imperfect wings, hidden in cases; furthermore, they have eyes hidden under the skin. The males and females alone have eyes; they also have wings, which they lose immediately after the coupling. Those which proceed from the pupæ with long wing cases become small kings and queens after their swarming, which takes place at the end of May. The pupæ with short wing-cases become perfect in the month of August, and produce larger males and females, which become kings and queens. All these couples are collected by the neuters; and the queens, large and small, set to work immediately to lay. The largest are much the more fruitful. The workers do not seem to take any care of them at all. With the exception of this last peculiarity, everything probably goes on in the same manner with the exotic termites; but with the latter the queen is an object of worship.
Fig. 383 represents the four types of the republic of theTermes lucifugus. On the left is a worker, on the right a soldier, in the centre a winged male, all three very much magnified, the lines drawn by their side showing the natural size. Below the male is the pregnant queen (D D D D), of a species of which we are about to speak, of the natural size.
Many species of termites were studied with care by the English traveller, Smeathman, at the end of the last century, in Southern Africa. His account of them is the most exact and most complete which we have of these insects.[111]The largest of the species observed is theTermes bellicosus. The workers are a fifth of an inch long, the body soft, and of an extreme delicacy, but the sharp mandibles capable of attacking the hardest bodies. The soldiers are twice as long, and weigh as much as fifteen workers, and may be distinguished by their enormous horned head, armed with sharp pincers. The male weighs as much as thirty workers, and attains to a length of nearly four-fifths of an inch.
Fig. 383.—Termes lucifugus. Male (A), Worker (B), Soldier (C), magnified. Fecundated female ofTermes bellicosus, natural size, surrounded by workers (D D D D).
But the pregnant female leaves all these dimensions far behind. Her abdomen becomes two thousand times as big as the rest of herbody! She then attains to six inches in length, and weighs as much as thirty thousand workers. By a hideous contrast, the head alone does not increase in size.d d d d(Fig. 383) is an exact representation of this monster. She is always motionless and captive in her cell, entirely occupied in laying. Her fecundity surpasses all bounds: sixty eggs a minute, more than 80,000 a day. Smeathman is inclined to think that this prodigious laying goes on during the whole of the year. "This soft, whitish beast," says M. Michelet, "a belly rather than a being, is as large, at least, as one's thumb; a traveller professes to have seen one of the size of a crawfish. The larger she is, the more fruitful, the more inexhaustible, this terrible insect-mother seems to be the more adored by the fanatical rabble. She seems to be their beau ideal, their poetry, their enthusiasm. If you carry away with any rubbish a portion of their city, you see them instantly set to work at the breach to build an arch which may protect the venerated head of the mother, to reconstruct her royal cell, which will become (if there are sufficient materials) the centre, the base of the restored city. I am not astonished, though, at the excessive love which this people show for this instrument of fecundity. If all other species did not combine to destroy them, this truly prodigious mother would make them masters of the world, and—what shall I say?—its only inhabitants. The fish alone would be left; but insects would perish. It suffices to be remembered that the mother-bee does not produce in a year what the female white ant can produce in a day. By her they would be enabled to devour everything; but they are weak and tasty, and so everything devours them."[112]In fact, birds are very greedy after termites; poultry destroy immense quantities of them. Ants give chase to them and eat them by legions. The negroes in Southern Africa cannot be sated with them. They gather such as have fallen into the water, and roast them like coffee; thus prepared, they eat them by handfuls, and find them delicious. The Indians smoke the termites' nests, and catch those that have wings. They knead them up with flour, and make a sort of cake of them. Travellers, moreover, all agree in speaking of them as very nice food, comparing their flavour to that of marrow or of a sugared cream. Smeathman prefers them to the famous palm worm (ver palmisteof the colonists), a delicacy known in South America, which is the larva of theCalandra palmarum, a species of beetle. It seems, however, that an abuse of fried termites brings on a dysentery which may prove mortal.
X.—Nest of the White Ant (Termes bellicosus),in Central Africa, after Smeathman.1. Male. 2, 4, 5. Neuters. 3. Gravid Female.
All the species of termites are miners, but the greater number are also architects and masons. A few make their nests round a branch of a tree. This nest is of enormous dimensions: it is as large as a tun. The illustration (Plate X.)—after a drawing in Smeathman's work—shows a nest of theTermes bellicosus, composed of bits of wood firmly stuck together with gum. Above their subterranean galleries the greater part of termites construct vast edifices, which contain their magazines and nurseries. TheTermes mordaxandTermes atroxraise perfect columns, surmounted by capitals which project beyond them and give them the appearance of monstrous mushrooms. These columns attain a height of twenty inches, with a diameter of five; they are constructed with a black clay, which, worked up by the insects, acquires great hardness. The interior is hollow, or rather perforated with irregular cells; but the most curious edifices are those ofTermes bellicosus. These are irregularly conical mounds, flanked by a certain number of turrets, decreasing in height. Smeathman gives them a height of from ten to twelve feet; but Jobson[113]affirms that he has seen some as high as twenty feet. If men constructed monuments so disproportionate to their size, the great pyramid of Giseh, instead of being 146 mètres in height, would be 1,600, and would be higher than the Puy-de-Dôme!
These knolls of earth are of a solidity which will bear any trial. Not only can many men mount on them without shaking them, but buffaloes establish themselves upon them as watch-towers, from which they can see over the high grass which covers the plain, if the lion or the panther is threatening them. These edifices are hollow; but their sides are from fifteen to twenty inches thick, and are as hard as a rock. They are hollowed out into galleries, which connect them with the underground dwelling. Under the dome is a pretty large vacant space, a sort of top storey or attic, occupying one-third of the total height, and which keeps up in the edifice a more uniform temperature than if all the block had been filled up. On a level with the ground is the royal cell, oblong, with a flat floor and a rounded ceiling, and pierced with round windows. All round are distributed the offices; they are rooms also with rounded and vaulted ceilings, communicating with each other by corridors. On the sides rise the magazines, with their backs placed against the walls of the house; they are filled with gums and with vegetable juices solidified and in powder. On the ceiling of the royal chamber rise pillars of abouttwo feet in height, which support the egg rooms. These are little cells with partitions of saw-dust stuck together with gum, which separate at the opening the large chambers from the clay halls. Placed between the attics and the great nave surmounting the royal hall, the nursery is in the most desirable position possible for uniformity of temperature and for ventilation.
The royal cell encloses a unique couple, objects of the most assiduous attentions, but kept in closest captivity, for the doors are too narrow to afford a passage to the monstrous queen, and even to the male, who keeps generally crouching by her side. Thousands of servants busy themselves round the mother; they feed her and carry away, night and day, the myriads of eggs which she lays. The eggs are placed in the egg houses, where they give birth to white larvæ, resembling the workers, which nourish themselves at first on a sort of mouldy fungus which grows on the partitions of their cells. They then become pupæ, then neuters, or males and females, the last two being provided with wings.
On a stormy evening the males and females come out of their nest by millions to couple in the air; then immediately afterwards they fall to the ground and lose their wings, when they become an easy prey to their enemies. A few couples only, picked up by the workers, are put under shelter, and become the nucleus of a new colony. The soldiers have no other occupation but to defend the nest. If man attacks them, at the first blow with the pick-axe they are to be seen running out furiously. They attack their aggressors, pierce them till they bring blood, and with their sharp pincers hang on to the wound, and allow themselves to be torn to pieces rather than leave go their hold. The negroes who have no clothes are soon put to flight; Europeans only get off with their trousers very much spotted with blood. During the combat, the soldiers strike from time to time on the ground with their pincers, and produce a little dry sound, to which the workers answer by a sort of whistling. The workers immediately make their appearance; and with their pellets of mortar set to work to stop up the holes, and to repair the damage. The soldiers then re-enter, with the exception of a small number, who remain to superintend the work of the masons; they give, at intervals, the usual signal, and the workers answer by a whistling which means, "Here we are!" as they redouble their activity. If the attack recommences, the soldiers are at their posts, defending the ground inch by inch. During this time the workers mask the passages, stop up the galleries, and wall up with care the royal cell. If you manage to penetrate as far as thissanctuary, you may pick up and carry away from the cell which contains them the precious couple without the workers in attendance on them interrupting their work, for they are blind.
They never venture in sight except in extreme cases. No one is ignorant of the terrible destruction these insects occasion to the works of man. Invisible to those whom they threaten, they push on their galleries to the very walls of their houses. They perforate the floors, the beams, the wood-work, the furniture, respecting always the surface of the objects attacked in such a manner that it is impossible to be aware of their hidden ravages. They even take care to prevent the buildings they eat away from falling by filling up with mortar the parts they have hollowed out. But these precautions are only employed if the place seems suitable, and if they intend to prolong their sojourn there. In the other case they destroy the wood with inconceivable rapidity. They have been known, in one single night, to pierce the whole of a table leg from top to bottom, and then the table itself; and then, still continuing to pierce their way, to descend through the opposite leg, after having devoured the contents of a trunk placed upon the table. On account of the devastations which they occasion, Linnæus has called the white ant the greatest plague of the Indies.
There exist in France two species of termites, theTermes lucifugus, a little insect of a brilliant black (at least in the male), with russety legs, which is common enough in the moors of Gascony; and the Yellow-necked White Ant (Termes flavicollis), which lives in the interior of trees and does a great deal of mischief in Spain and in the south of France to olive and other precious trees, whilst the first attacks oak and fir trees. Latreille established that it is theTermes lucifuguswhich causes such havoc at La Rochelle, at Rochefort, at Saintes, at Tournay-Charente, in the Isle of Aix, &c., where many houses have been completely undermined by these terrible insects. But M. de Quatrefages[114]has proved that the habits of the termes found in towns differ in many essential points from the habits of termes in the country. And so it is most probable that the former belong to an exotic species, which must have been unfortunately imported into France by a merchant vessel. According to M. Bobe-Moreau,[115]it was only in 1797 that termites were discovered for the first time in Rochefort, in a house which had stood for a long whileuninhabited, and which they had completely undermined. In 1804, Latreille relates, as a "hearsay," that the termites had for some years made the inhabitants of Rochefort uneasy; but in 1829 the same author tells a very different tale. He speaks with dismay of the ravages committed by this insect in the workshops belonging to the Royal Navy. The importation of the termes into France is then of recent date. A note which was sent to M. de Quatrefages by M. Beltrémieux, fixes with still greater accuracy the date of the importation of the termites; it must have taken place about 1780, a period at which the brothers Poupet, rich shipowners, caused bales of goods to come from St. Domingo to Rochefort, to La Rochelle, and to other places in that neighbourhood which possess storehouses. The ravages which the termites have committed in the towns of La Saintonge are really frightful. Like Valencia, in New Granada, these towns will find themselves one of these days suspended over catacombs. At Tournay-Charente, the floor of a dining-room fell in, and the Amphytrion and his guests tumbled together in the cellar. There may be seen in the galleries of the Museum of Natural History of Paris the wooden columns which supported this room, and which were preserved by Audouin, who had been sent on a mission to report on the damages done. Audouin also selected, as an object of curiosity, a lady's bridal veil, which had been entirely riddled with holes by the termites.
At La Rochelle these insects took possession of the Prefect's house (built by the brothers Poupet), and of the Arsenal. There they invaded offices, apartments, court, and garden. They could not drive in a stake, or leave a plank in the garden, but it was attacked the next day. One fine morning the archives of the department were found destroyed, without there being the smallest trace of the damage to be seen on the exterior. The termites had mined through the wood-work, pierced the cardboard, eaten up the parchments and the papers of the administration, but had always scrupulously respected the upper leaf and edges of all the leaves. It was by mere chance that a clerk, less superficial than his colleagues, one fine day raised one of the leaves which hid thisdetritus, and thus discovered the destruction of the archives. All the papers of the Prefecture are now shut up in boxes of zinc.
These termites do not venture, any more than their congeners, into the light of day. These terrible miners always envelop themselves in obscurity, and construct on all sides covered galleries as they advance into a building. M. Blanchard and M. de Quatrefages saw in La Rochelle the galleries made by them. They are tubesformed of agglutinated material, which are stuck along the walls in the cellars and the apartments, or else suspended to the roof like stalactites. Certain parts of Agen and of Bordeaux begin also to suffer from the ravages of these insects. The danger appears to be imminent.
We are indebted to M. de Quatrefages for some interesting experiments on the termites of La Rochelle. Not only has the learned naturalist helped to make known to us the habits of these dark-loving insects, but he has also told us how to destroy them. Different substances have been tried in vain to stop these terrible ravages—essence of turpentine, arsenical soap, boiling lye, &c. M. de Quatrefages had recourse to gaseous injections. He tried successively binoxide of nitrogen, nitric acid, chlorine and sulphurous acid; chlorine, above all, fully answered his hopes. With pure chlorine he killed the termites instantaneously; mixed with nine-tenths of air, he suffocated them in half an hour. "For attacking the termites," says M. de Quatrefages, "one ought to choose by preference the period of their reproduction, so as to destroy the pregnant females. It is probable that, like their exotic congeners, the termites of France will endeavour to defend themselves by walling up the interior of their galleries at the first signs of an attack. The operator must then act with a great deal of promptitude, and direct the apparatus as much as possible into the very centre of their habitation, where the galleries are the broadest and the most numerous.
"With whatever care one acts, and whatever may be the success of a first attempt, it seems to me impossible to destroy in one campaign all the termites of a locality. In this, as in all operations of the same kind, a certain amount of perseverance is necessary, especially if it is in a town or in a country infested by them to a very great degree; in that case one will be forced to repeat the operation from time to time. When, on the contrary, the termites are already cantoned, it seems to me that the success ought to be lasting. This is fortunately the case at La Rochelle; and by knowing how to profit by it, one may doubtlessly prevent the spread of these pests, which at one time or another, may attack the whole town."[116]
In 1864 the Lords of the English Admiralty addressed an inquiry to the Entomological Society of London, on the best means of preserving wood from the attacks of the Indian termites. In answer to this inquiry, the Entomological Society recommended many processes:the injection of quicklime or of creosote, the application of arsenical soap, &c. But it does not appear that these processes are infallibly efficacious, nor, above all, easy to employ.
Among other Neuroptera which undergo incomplete metamorphoses, we may mention, first, the generaPerlaandNemoura,[117](Figs.384,385, and386), which flutter about the banks of rivers, and settle on stones, shrubs, and aquatic plants. Their larvæ are naked, without cases, and always live in the water, hiding themselves under stones, to watch for small insects, for they are carnivorous. One sees them often balancing their bodies, holding on to a pebble. They go through the winter, and only become pupæ in the spring. After moulting, they have the rudiments of wings. Very soon afterwards the pupæ leave the water, and undergo their metamorphosis. The adult lives only a few days, for its mouth is not suited for receiving food. The larvæ have, at the end of their bodies, two long threads, which remain in the perfectPerla, but not in the perfectNemoura; the latter lose the two caudal hairs when they arrive at the adult state. One species ofPerlais very common on the quays of Paris.
Fig. 387.—Perla bicaudata.
TheEphemeridæ, or May-Fly family, have long, slender bodies,provided with two or three long silky hairs. Their name indicates the short duration of their existence. They appear in great numbers at certain seasons of the year. Their hatching takes place at sunset; they have coupled and laid their eggs by sunrise next day, and have ceased to live; so that the banks of rivers, of ponds, of lakes, are strewed with their bodies. Their number is sometimes so considerable that, according to Réaumur, the soil seems as if it were covered with snow, and they are gathered up for manure. The common Ephemera, or May-Fly (Ephemera vulgata,Fig. 390), is of a brown colour, banded with yellow, and the wings smoky, with brown spots. These insects are remarkable for their elegant flight; they are continually rising and falling. When they move their wings they rise; but if their wings, though spread out, remain motionless, as also the silky hairs which form their tail, they fall again. They may be seen in myriads in places where there is much water.
Fig. 408.—Ephemera vulgata, imago.Fig. 390.Ephemera vulgata, imago.
We have said that theEphemerælive only for a few hours. This is the general rule; but their existence can be prolonged for ten or fifteen days by preventing their copulation. If, however, the duration of the life of these insects is so short when they have reached the perfect state, and when the conformation of the mouth prevents them from taking any nourishment, their larvæ state is of very long continuance. Swammerdam says, in his curious Memoir, entitled "Vita Ephemeri," it is not less than three years.
The females lay their eggs in one single mass, and let them fall into the water, in the form of a packet. The larvæ which come out of them are very active, and swim with great ease; but generally conceal themselves under the pebbles at the bottom. The sides of their abdomen are provided with gills, very much fringed, which serve them, not only for breathing the air under the water in the same way that fish do, but also for swimming. The larvæ have, at the extremity of their body, two or three hairs, like the perfect insect. They hollow out galleries in the beds of rivers and ponds, and live on small insects.The pupa (Fig. 392) differs only from the larva (Fig. 391) in having the rudiments of wings. When about to undergo their metamorphosis, they come out of the water and cling to plants, &c. The skin cracks on the back when it is dry, and there comes out a heavy insect, which flies feebly, and has opaque wings. It is still enveloped in a very thin skin, of which a last moult, after a few hours, frees it. This skin remains sticking to the plant on which the moulting was effected, preserving the shape of the insect. This moult is peculiar to theEphemeræ; it is the transition from the false imago (pseudo-imago) to the imago.
In the same family is the genusCloëon, whose larvæ prey on minute insects. TheCloëon diptera(Fig. 393), which has only two wings, is often to be met with in houses, resting on the window panes and curtains. All these insects keep badly in collections; they lose their shape, and their members are so fragile that the least shock suffices to break them.
TheLibellulas, or Dragon-Flies, are insects of a well-defined type.The elegance of their shape, the grace of their movements, have won for them among the French their common appellation of "Demoiselles." They are always of largish size. Many are of bright and metallic colours, which are not inferior in beauty to those of butterflies. Their wings, of an extreme delicacy, always glossy and brilliant, present varied tints; sometimes they are completely transparent, and have all the colours of the rainbow. Often, the colour of the males differs from that of the females. They may be seen fluttering about on the water during the whole summer, especially when the sun is at its highest. They fly with extreme rapidity, skimming over the water at intervals, and escaping easily when one wishes to catch them. Nothing is prettier than a troop of dragon-flies taking their sport on the side of a pond or on the banks of a river, on a fine summer's day, when a burning sun causes their wings to shine with most vivid colours.
Fig. 393.—Cloëon diptera.Fig. 393.—Cloëon diptera.
In the perfect state, as well as in that of the larva and the pupa, theLibellulæare carnivorous. Their rapid flight makes them expert hunters, and their enormous eyes embrace the whole horizon. They seize, while on the wing, flies and butterflies, and tear them to pieces immediately with their strong mandibles. Sometimes, the ardour of the chase leading them on far from the streams, they are met with in the fields. The female lays her eggs in the water, from which emerge larvæ which remind one somewhat of the form of the insect, only their body is more compact and their head flattened. The larvæ and pupæ inhabit the bottom of ponds and streams, where, keeping out of sight in the mud, they seek for insects, molluscs, small fish, &c. If any prey passes within their reach, they dart forward, like a spring, a very singular arm, which represents the under lip. It is a sort of animated mask, armed with strong jagged pincers and supported by strong joints, the which, taken together, is equal to the length of the body itself. This mask acts at the same time as a lipand an arm; it seizes the prey on its passage, and conveys it to the mouth. "When any aquatic insect approaches them at a time when they are in a humour for eating," says Charles de Geer, "they shoot the mask forward very suddenly and like a flash of lightning, and seize the insect between their two pincers; then, drawing back the mask, they bring the prey up to their mandibles, and begin to eat it. I have remarked that they do not spare those of their own kind, but that they eat each other up when they can, and I have also seen them devouring very small fish which I put by them. It is very difficult for other insects to avoid their blows, because, walking along generally in the water very gently, and, as it were, with measured steps—almost in the same way a cat does on the look-out for birds—they suddenly dart forward their mask and seize their prey instantaneously."[118]Fig. 394represents, to the left, the larva of the dragon-fly, with theinstrument of attack which we have called a "mask," and which it is making use of for seizing a small insect; on the right, the adult dragon-fly coming out of the nymph.
Fig. 394.—Larva of the Libellula, and the perfect insect emerging.Fig. 394.—Larva of theLibellula, and the perfect insect emerging.
The respiration of these larvæ is very singular. Their abdomen is terminated by appendages, which they open to allow the water to penetrate into the digestive tube, the sides of which are furnished with gills communicating with the tracheæ. The water, deprived of oxygen, is then thrown out, and the larva advances thus in the water by the recoil. It has no tufts of external lateral gills, which in the case of theEphemerædo the duty of fins. The pupa already presents stumps of wings. To effect its metamorphosis it drags itself out of the water, where it has lived for nearly a year, climbs slowly to some neighbouring plant, and hangs itself there. Very soon the sun dries and hardens its skin, which all of a sudden becomes crisp, and cracks. The dragon-fly then sets free its head and its thorax, and its legs; its wings, still soft and wanting in vigour, gain strength by coming in contact with the air, and, after a few hours, they have attained their full development. Immediately the insect abandons, like a worn-out suit, the dull slimy skin which had covered it so long, and which still preserves its shape (Fig. 394), and dashes off in quest of prey.
Fig. 395.—Libellula depressa, the Common Dragon-Fly.Fig. 395.—Libellula depressa, the Common Dragon-Fly.
TheLibellulasare common all over the world. Their type is theLibellula depressa(Fig. 395), very common in Europe. The male isbrown, with the abdomen blue underneath; the female, of a sort of olive-yellow, bordered by yellow on the sides. Both have the abdomen broad and flattened.
TheÆshna, with a cylindrical abdomen, attains to the length of two and a half inches. Its flight is more rapid than that of the swallow. TheCalepteryxflies more slowly. The male is of a metallic blue, its diaphanous wings are traversed by a band of greenish blue; the female, of a bronzed green, has wings of a metallic green, with a yellowish mark on the edge. These insects rest on reeds, retaining their wings in a vertical position.
TheAgrions, which are of the same family, have the body white, brown, or green, and the eyes very prominent. They are more slim and graceful than theLibellulas, properly so called; their larva are very elongated.
Fig. 399.—Mantispa pagana.
In the spring, one meets in the woods with insects having large heads and elongated thoraces. The females have a long auger, with which to deposit their eggs under the bark of trees, where their larvæ, which feed on insects, and twist themselves about like small serpents, live. The pupæ are also very active; they resemble the adults very much, and have the wings laid against the body. These insects, which are met with everywhere, but always in small numbers, are theRaphidias, which we see represented (Figs.396,397,398) in the state of larva, pupa, and adult, and theMantispas(Fig. 399), one species of which is common in the south of Europe.
Fig. 400.—Semblis lutarius, imago, pupa, and larva.Fig. 400.—Semblis lutarius, imago, pupa, and larva.
M. Blanchard classes in the same tribe the genusSemblis, whose larvæ are aquatic, with scaly heads, provided with eyes, and with curved mandibles and short antennæ. The larvæ and the pupæ breathe, like those of theEphemeræ, by articulated external processes, or gills, analogous to those of fishes. Nevertheless the pupæ live on land, not in water. They hide themselves in the earth at the foot of trees, and the adult issues forth at the end of a fortnight, leaving its pupa skin behind. It lives but a few days. The female lays her eggs on reeds, stones, &c.Fig. 400represents the MudSemblisin its three states.
Fig. 401.—Ant-lionFig. 401.—Ant-lion (Myrmeleo formicarius).
We now come to those Neuroptera which undergo complete metamorphoses. They are the Myrmeleonidæ, of which the Ant-lion (Myrmeleo) is the most prominent type, and thePhryganidæ, or Caddis Flies.
The larvæ of the Ant-lions live on the land, and are carnivorous. When about to undergo their transformation into pupæ, they spin forthemselves a silky cocoon. The larvæ of thePhryganeas, on the contrary, live in the water. They surround themselves with a sort of protecting case, composed of a silky shell and incrustations of all sorts. The pupæ, as well as the larvæ of these insects, breathe by means of gills.
The Ant-lion (Myrmeleo formicarius,Fig. 401) is found in the environs of Paris. It is an elegant insect, resembling the dragon-fly, but is distinguished from it by its antennæ. Its larva is of a rosy, rather dirty grey, with little tufts of blackish hair on its very voluminous abdomen. Its legs are rather long and slender; the two anterior pair of legs are directed forwards, whilst the hind legs are fixed against the body, and only permit the animal to walk backwards. These larvæ are met with in great abundance in sandy places very much exposed to the heat of the sun. There they construct for themselves a sort of funnel in the sand (Fig. 402), by describing, backwards, the turns of a spiral whose diameter gradually diminishes. Their strong square head serves them as a spade with which to throw the sand far away: they then hide themselves at the bottom of the hole, their head alone being out, and wait with patience for some insect to come near. Scarcely has the ant-lion perceived its victim on the borders of its funnel, when it throws at it a shower of dust to alarm it, and make it fall to the bottom of the precipice, which does not fail to happen. Then it seizes it with its sharp mandibles, andsucks its blood; after which it throws its empty skin out of the hole and resumes the look-out. Ants especially become its prey, whence its name of Ant-lion. Towards the month of July, the larvæ make themselves a spherical cocoon, mixed with grains of sand, in which they are transformed into pupæ which are hatched towards the end of August. The perfect ant-lions diffuse an odour of roses; their flight, which is weak, distinguishes them from the dragon-flies. We meet in the south of France with a very beautiful species of Ant-lion, theMyrmeleo libelluloides(Fig. 404); its larva can move forwards, and does not dig itself a funnel.
Fig. 404.—Myrmeleo libelluloides.
The genusAscalaphus(Fig. 407) is remarkable for the long clubbed antennæ of its members, and for their rapid flight. They like the sun, and live especially in hot countries; however, one meets with theAscalaphus, in the month of July, near Paris, on the dry declivities of Lardy and of Poquency. Their larvæ (Fig. 406) have mandibles adapted for suction. They watch for insects under heaps of stones, and spring upon their prey.
The first states of theNemoptera[119](Fig. 408) are as yet little known. They are insects with wings spotted with yellow and black, the lower ones almost linear, and are met with in southern countries, and but very rarely in the south of France.
TheHemerobii, to which are given by the French the name ofDemoiselles terrestres, or Land Dragon-Flies, are very small delicate insects, of an apple-green colour, with golden red eyes. These insects leave on the fingers, when seized, an offensive odour. Réaumur calls themLions des pucerons(Plant-Lice Lions), because their larvæ, which resembles the larvæ of the ant-lions, and which live on plants, feed onplant-lice. They attack also caterpillars. Their mandibles are provided with a canal for suction, like those of the foregoing species.
The insects of the genusOsmylus(Fig. 409) are rather rare; but may be found in the shrubs which border ponds. They also belong to theHemerobidæ. Their larvæ live in wet ground.
Fig. 410.—Panorpa, male and female.Fig. 410.—Panorpa, male and female.
ThePanorpatæconstitute a singular little family, having a peculiar shaped head, which is prolonged to a sort of long and slender beak. Aristotle called them Scorpion Flies, and thought they were winged scorpions. ThePanorpas, properly so called (Fig. 410), are found on hedges and plants during the summer.They have slim bodies spotted with yellow and black, and four straight wings, also spotted with black. In the males the abdomen terminates in a pair of pincers (Fig. 411), which rather remind one of the tail of a scorpion, and which are destined to seize their prey, which they kill by piercing with their beak. The female lays her eggs in the ground (Fig. 412). In a week the larva makes its appearance; it is a month in developing, it then buries itself still deeper in the earth, and changes into a pupa, which, after a fortnight, comes again into the light in the form of a perfect insect. There are two other genera ofPanorpatæ, of whichBittacus tipularis(Fig. 413), resembling a large gnat, furnished with four wings, andBoreus hyemalis(Fig. 414), of a brilliant black, met with in Sweden and in the elevated parts of the Alps, jumping about on the snow in considerable troops—are representatives. The latter has been found in England.
ThePhryganidæ, or Caddis Flies, are known by their larvæ, of which anglers make great use. Réaumur classed them as aquatic moths. The soft and delicate body of the larvæ is protected by a case, to which they cling by two hooks, placed at the extremity of their abdomen. They are called by different names in allusion to their habits; as, for instance, case worms, from their living in a case covered with little bits of wood or sand, which they draw after them as they go. Their scientific name,Phryganea, signifiesfagot.[120]ThePhryganeæ, in the adult state, very much resemble moths. They approach them in having rudimentary mouths, and wings without articulations, but furnished with small hairs, analogous to the scales of Lepidoptera. They may be said to form a sort of connection between the Lepidoptera and Neuroptera. They have been calledMouches papilionacées, or Papilionaceous Flies. The eggs laid by the femalePhryganeaare enclosed in gelatinous capsules, which swell in the water and attach themselves to stones, &c. The larva has the appearance of a little worm without feet. It is soon hatched, and resembles at first a little black line, and may be easily reared in an aquarium. The operation of making the silky case which it draws after it, and which protects its abdomen, may then be observed. When it is disturbed, it retreats entirely within its case. The interior is smooth, and lined with mud; on the exterior it is fortified with stones, &c.
Fig. 418.Regular cases of a Phryganea.
ThePhryganea rhombica(Figs.415,416,417) furnishes its case with bits of wood or grass, arranged as shown inFig. 418. Some species arrange these bits of wood and glass in spiral, others in parallel series. ThePhryganea flavicorniscovers its dwelling with little shells. "These kinds of dress," says Réaumur, "are very pretty, but they are also excessively singular. A savage who, instead of being covered with furs, should be covered with musk rats, moles, or other entire animals, would have on an extraordinary costume; this is in some sort the case with our larvæ." OtherPhryganeæemploy for constructing the case which serves them as a dwelling sand and small pebbles; each species always employing the same materials, unless they are entirely deprived of these and obliged to employ others. These cases protect the larvæ against the voracity of their enemies. The larvæ have a scaly head; and the three first rings of their body are harder than the rest. They live in water, and breathe by means of branchious sacs, arranged on the abdomen in soft and flexible tufts. They eat everything that is presented to them: leaves, and even insects and the larvæ of their own kind. The pupæ are motionless. They stay about a fortnight in their case, the orifice of which is closed by gratings of silk, then break through the gratings, and leave their prison. In this state (Fig. 419) they swim on the water until they meet with an object to which they can attach themselves, and so get out. Then they swell till they crack their skin over the back, and the perfect insect emerges.
ThePhryganea pilosa(Fig. 420) is of a yellowish grey, with hairy wings, little adapted for flying. These insects do not eat, and never leave the neighbourhood of the water. During the day they rest on flowers, on walls, or on the trunks of trees, their wings folded back, and their antennæ together. In the evening they fly in dense swarms over streams and ponds. They are attracted by light, as are many nocturnal insects; and are sometimes found in great numbers on the lamps on the quays in Paris.
TheHydropsyches(Fig. 421) andRhyacophili(Fig. 422) are small insects which resemble thePhryganeævery closely. Their larvæ have, for the purposes of respiration, some gills, others retractile tubes. They construct for themselves fixed places of shelter, more or less imperfect, at the bottom of the water, and against large stones,which they leave occasionally for a few moments. Sometimes these cases contain several larvæ.Fig. 421represents the various states of aHydropsyche; the larva is seen on the left, the pupa on the right, the winged insect in the middle. Two of the insect's tents, or places of shelter, are represented below.Fig. 422shows the different states ofRhyacophilus vulgatus, larva, cocoon, pupa, and imago. The genusRhyacophilushas this peculiarity, that the larva spins itself a cocoon in the interior of its dwelling before changing into a pupa.
Fig. 421.—Hydropsyche (Phryganea) atomaria, larva, pupa, imago, and larva-case.Fig. 421.—Hydropsyche (Phryganea) atomaria, larva, pupa, imago, and larva-case.
Fig. 422.—Rhyacophilus vulgatus, larva, pupa, cocoon, and imago (male).Fig. 422.—Rhyacophilus vulgatus, larva, pupa, cocoon, and imago (male).