Fig. 8. Salticus scenicus, female, × 4.Fig. 8.Salticus scenicus, female, × 4.
Fig. 8.Salticus scenicus, female, × 4.
It is one of the largest groups, numbering severalthousand species, but the British list includes barely thirty, and most of these are of rare occurrence, or at all events exceedingly unlikely to be met with by any but the most energetic collector. Indeed it may be said that there is only one British species which we may look forward with tolerable confidence to finding upon some sunny wall or fence in the summer, in whatever part of the country we may be. This isSalticus scenicus, sometimes called the Zebra Spider. Though absolutely dowdy in comparison with most of its tropical cousins, it is a not unattractive little creature, and illustrates sufficiently well the characteristics of its tribe. Armed with a pocket-lens, a glass tube or two, and—more necessary still—the very largest amount of patience we can summon, we go in quest of the zebra spider. A tarred fence is a good hunting ground, because the spider, if present,is readily seen, but if this is drawn blank we must have recourse to a wall, where sharper eyesight will be required.
Fig. 9. “Face” of an Attid spider, shewing the anterior eyes and the chelicerae.Fig. 9. “Face” of an Attid spider, shewing the anterior eyes and the chelicerae.
Fig. 9. “Face” of an Attid spider, shewing the anterior eyes and the chelicerae.
Our quarry is of small size, not more than a quarter of an inch long in the body, which resembles that of the wolf-spiders in build, the abdomen not rising above the level of the fore-body or cephalothorax. It is thickly clothed with short hairs—black, white, and grey—so arranged as to show oblique zebra-like stripes on either side of the abdomen. The legs are short and robust, very different from the long thin limbs of the garden-spider; especially strong are the fore-legs. The head is broad and square, with a high perpendicular forehead, but the most remarkable features are the eyes.
On the vertical front are four splendid eyes. The wolf-spider’s eyes were large, but these, in comparison, are immense, especially the median pair. Their axes are directed straight in front. Four other eyes areplaced on the top of the head, far apart from each other, the more forward pair very small, the hind pair of moderate size. In some Attid spiders these great anterior eyes are wonderful objects under the microscope, deep sea-green in hue and fringed with coloured hairs. They form a veritable battery which the spider brings to bear upon the object of its chase. Human eyes, to match them in comparative size, would literally have to be as large as saucers!
If we are in luck, we soon descry aSalticusshowing up boldly against the black surface of the fence, and to set ourselves to watch its antics attentively. One thing strikes us at once; it is quite at home on a perpendicular surface—nay, on the under side of a horizontal beam, for that matter. Now a garden-spider would have great difficulty in maintaining itself in such a position unless well supplied with silken lines to which to cling; evidently there is some difference in the structure of the feet of these spiders which may be worth investigating later on.
Also we notice some odd tricks of movement in the jumping spider; a curious way of exploring the surface on which it is working by a succession of short runs alternately with periods of absolute stillness as though on thequi vive; a noticeable freedom of movement between the fore- and the hind-bodies so that its battery of eyes may be directed to this side or that; sometimes an elevation of fore partas though for the purpose of obtaining a wider view.
We may have to wait long before we see it successful in the chase. It will often patiently explore a large area, testing the surface with its palps as it goes, without any obvious reward. It conscientiously searches all depressions and crannies, and, sometimes remains in them for a considerable time—perhaps to devour some minute creature which did not call into play its special methods of attack. At last it sights a small insect which has alighted on the fence a few inches away; we see it turn its head in that direction and remain motionless. Soon it begins to edge nearer in a stealthy manner, striving to approach its prey from behind, till, with a sudden spring, it pounces on its back. Not always is the spring successful; often the insect sees its peril at the last moment and takes to wing. But in this case, how does the spider avoid a fall? We see, what we had not noticed before, that it is anchored to the fence by a silken line; indeed all the time it has been hunting it has been trailing behind it an exceedingly fine thread of silk which it has attached at frequent intervals to the fence, so that it can check its fall at will in the case of accident. At the right angle, we may see the delicate filaments glistening in the sun over the surface of its explorations. The garden-spider entangles its prey in a web,the wolf-spider runs it down by sheer strength and speed, but the jumping spider stalks it like a Red Indian.
The actions of the spider make it quite evident that its power of sight is well developed. Mr and Mrs Peckham, whose remarkable observations on the mating habits of jumping spiders must presently be considered, established friendly relations with some of their captives which became so tame as to jump on their hands and take food from their fingers. They frequently induced them to jump from a finger of one hand to one of the other, gradually increasing the distance up to eight inches. They also twice observed a male chasing a female upon a table covered with jars, books and boxes. “The female would leap rapidly from one object to another, or would dart over the edge of a book or a box so as to be out of sight. In this position she would remain quiet for a few moments and then, creeping to the edge, would peer over to see if the male were still pursuing her. If he happened not to be hidden, she would seem to see him, even when ten or twelve inches away, and would quickly draw back.”
Moreover that they have the ability to discriminate colours has been shown by their behaviour when imprisoned in cages consisting of a series of communicating chambers each with a glass top of a different hue. They show a marked preference forthe red chamber under these circumstances while the least attractive colour seems to be blue.
It has been known for a long time that the males of many kinds of birds—and especially of the more ornamental species—are accustomed to perform the most extraordinary antics in the presence of the female at the time of mating. The Peckhams made the unexpected discovery that precisely similar “love dances” took place in the case of the jumping spiders. Even the comparatively sober-coloured “zebra spider” performs a weirdpas seulin courting its mate, but its display is feeble compared with that of some of the more ornate of the Attidae.
Certain isolated observations on captive jumping spiders led these observers to suspect that the mating habits were unusual and worthy of accurate investigation, and they laid their plans accordingly, taking their summer holiday a month earlier than usual, so as to miss nothing of the pairing season, and including in their party an artist whose drawings should furnish an indubitable record of the attitudes assumed by the male spiders in their evolutions.
On arriving at their destination they found a small species,Saitis pulex, with no great claims to remarkable beauty, mature, and ready to pair. A female was placed in one of the experimental boxes which had been provided in advance, and a male was admitted on the following day. He sighted her ata distance of twelve inches, and showing signs of excitement, advanced to within about four inches and then performed a most ludicrous dance—something in the nature of a “highland fling,” in a semicircle before her, she, in the meantime, moving in such a manner as to keep him always in view. His exact behaviour was this: he extended all the legs—and the palp—on the left side, folding the first two legs and the palp of the right side under him, and leaning over sideways so far as nearly to lose his balance, and in this attitude he sidled along towards the lowered (right) side till he had described an arc of about two inches; then the position was instantly reversed, the right legs being extended and the left folded under, and the arc retraced. A male was seen to repeat this performance 111 times! He then approached nearer and when almost within reach “whirled madly around and around her, she joining and whirling with him,” after which she accepted him as a mate.
The next species to engage attention was anIcius. It was noteworthy that although the neighbourhood was well known to the experimenters they had never met with this spider before, but for a few days it swarmed on the fences just as birds are known to assemble from all quarters for the so-called “love dances.” After the mating season the spiders wandered off into the woods again and were seen no more.
Fig. 10. A male Attid spider (Astia vittata) dancing before the female. (After Peckham.)Fig. 10. A male Attid spider (Astia vittata) dancing before the female. (After Peckham.)
Fig. 10. A male Attid spider (Astia vittata) dancing before the female. (After Peckham.)
The performance was much as before, but the spiders assumed different attitudes. The female lay flat on the ground with her front legs raised; the male danced on the six hind legs, with the front legs lowered and meeting at the tips. The males of this species were exceedingly quarrelsome, sparring frantically whenever they met, but their battles were entirely bloodless. “Indeed,” say the observers, “having watched hundreds of seemingly terrible battles between the males of this and other species, the conclusion has been forced upon us that they are all sham affairs, gotten up for the purpose of displaying before the females, who commonly stand by, interested spectators.” In the case of one species,after two weeks of hard fighting between the males, the Peckhams were unable to discover one wounded warrior. The females, on the other hand, were often really formidable.Phidippus morsitansis an example. The male has handsome front legs, thickly fringed with white hairs, and he displays these to the best advantage in his love antics. Two males supplied in succession to one female “had offered her only the merest civilities when she leaped upon them and killed them.”
In the case of most of the spiders whose love-dances were investigated, the chief ornamentation of the male consisted of fringes of white or coloured hairs on the face, the palps, and the front legs, and they kept these parts always before the females, displaying their glories to the utmost advantage. The male ofHabrocestum splendens, however, possesses an extremely brilliant abdomen, and, lest anything of its beauty should be lost upon the object of his admiration, he varies the ordinary performance in a remarkable manner. He often pauses in the dance, and, raising his abdomen, “strikes an attitude” in which he remains motionless for half a minute. Moreover he frequently turns his back on the female—a most unusual occurrence in the course of these antics.
The males of one species,Philaeus militaris, were observed to capture and keep guard over youngfemales, which they imprisoned in webs spun for the purpose until they had undergone their last moult and were mature, chasing away all intruders in the interval.
The jumping spiders furnish a much stronger case for those who believe that ornamentation plays an important part in sexual selection than do either birds or butterflies. With regard to the birds it has been objected, first, that there is little evidence that the females pay much attention to the antics of the males, and secondly, that practically all the male birds pair, whatever their claims to pre-eminent beauty. Now in the case of the jumping spiders the females follow the performances of the males with the utmost attention, and seeing that the males are present in large numbers when the females begin to appear, the latter are certainly in the position to reject such mates as do not please them.
The mere relation of the results of this most interesting investigation conveys no hint of the unwearied patience and close observation necessary to those who would surprise the secrets of nature. One is apt to infer that it is only needful to place some spiders in a box, establish oneself in an arm chair, and ring on the performance, so to speak. The Peckhams modestly remark: “The courtship of spiders is a very tedious affair. We shall condense our descriptions as much as possible, but it must benoted that we often worked four or five hours a day for a week in getting a fair idea of the habits of a single species.”
THERAPHOSID SPIDERS
Itis quite impossible in a work like the present to deal with the classification of spiders. About forty families have been established, some of them of vast extent, the Attidae, for example, including some four thousand species. The great French arachnologist, M. E. Simon, has occupied 2,000 quarto pages in defining the families, sub-families and genera, without concerning himself with the species at all! It is, however, desirable, that the attention of the reader should be called to the primary division of the group, according to which all spiders are eitherAraneae verae(true spiders) orAraneae theraphosae(theraphosid spiders.)
Now these two kinds of spider may readily be distinguished by a single easily observable characteristic, the nature of the mandibles orchelicerae; but it is necessary to describe the spider’s mandibles before the difference can be appreciated.
Their nature is perhaps best explained by saying that each mandible is not unlike a penknife witha single small blade, rather more than half open when in use, closed when at rest. The handle of the penknife is certainly in most cases very short and thick, and the blade not really a blade at all, for it has no cutting edge, but is a “fang” or piercing instrument generally somewhat curved, and with a sharp point. The “blade” is, moreover, perforated by a tube which comes from the poison-gland, situated in the thickened “handle,” or in the spider’s head, so that poison can be forced into the wound which it inflicts.
Now take two penknives with the blades half open and hold them so that they hang with the hinge downward and with the blades directed towards each other; it is clear that the blades may be made to pierce an object situated between them by moving the handles laterally, the object being attacked simultaneously on either side. This is the arrangement in the true spiders, whose jaws move sideways, though they do not always hang perpendicularly, but are more often somewhat slanted forwards.
To represent the jaws of a theraphosid spider the penknives must be arranged differently. Place the handles horizontally and parallel to each other, with the blades directed downwards and also parallel. They will now work not sideways, but up and down, and both fangs will pierce the victim from above. In a word, the true spiders have jaws which can beseparated or brought together, and which tend to meet in the object into which they are plunged, while the jaws of theraphosid spiders work in parallel vertical planes, and strike downwards.
All the spiders which have so far concerned us areAraneae verae, and we have incidentally had occasion to note some of the principal families of that division—Epeiridae (or Argiopidae as some prefer to call them), Theridiidae, Agelenidae, Thomisidae, Lycosidae and Attidae.
Indeed there is only one theraphosid spider that there is the least likelihood of our coming across in this country. Their true home is in hotter climes, and though stragglers from their army are not rare in the warmer portions of temperate regions, they abound only in tropical countries. They include the “Trap-door” spiders, common in the Mediterranean region and in many other widely distant parts of the world, and the great “Bird-eating” spiders of the tropics—the spiders which are quite wrongly but universally alluded to in America as Tarantulas.
The single British example is well worth the study of any reader who is fortunate enough to come across it. But he must first catch his hare, forAtypus affinis(orpiceusas it used to be called) does not grow in every hedge-row, nor is it easy to find it where it does occur. Most of the localities recorded are in the south of England. It is a thick-setdark-coloured spider about half an inch in length, and with very thick, powerful mandibles, which, as we have seen, work vertically.
Its nest is a loosely-woven tubular structure, which partly lines a more or less vertical hole in the ground and partly lies exposed on the surface, but which does not present any obvious opening for entrance and exit.
The situation chosen is generally a sloping sandy bank covered with vegetation. The burrow is about eight inches in depth and about three quarters of an inch in diameter. Near the bottom it narrows and then expands into a somewhat wider chamber where the spider lives and constructs its egg-cocoon. The portion of the tube above the ground is sometimes longer but more often shorter than the buried portion, and it tapers to a closed end.
Mr Joshua Brown, who first found this spider near Hastings in 1856, took home several of the tubes with the spiders inside. He could find no opening, and though the spiders moved up and down the tubes they did not emerge. On tearing a tube open he found no remains of insects inside, but in one case he came across a worm, partly within, and partly outside the lower part of the tube, and apparently partially devoured by the spider.
The same species is not rare in France and M. Simon’s observations on it closely agreed with thoseof Mr Brown. He believed that the spider chiefly depended for its food on earthworms which, in the course of their burrowings, came casually into its neighbourhood. Since these observations, however, considerable light has been thrown on the habits of the spider by Enock, who found colonies on Hampstead Heath and near Woking. His investigations extended over several years, and wonderful patience was needed before the secrets of this curious animal were divulged.
It appears that the female, when once established, never leaves the nest at all! The aerial portion of the web was always a puzzle, but now we know, thanks to Enock, that it constitutes the whole hunting ground of the spider. Like promises and pie-crust it is apparently made to be broken. If it is accidentally brushed against by a passing insect the spider is instantly aware of the fact, rushes to the spot, and transfixes the intruder with its powerful mandibles. It turns on its back to do this, and strikes the insect from behind, afterwards pulling its prey through the weft and into the tube by main force. It drags it to the bottom of the tunnel, makes sure of its death, and immediately returns and repairs the rent.
Insects were held against the tube, and the spider, if hungry, accepted them at once; if replete however, it always gave a tug at the tube, which retracted a portion of it into the burrow—a curious actionwhich Enock quite learnt to interpret as the “I don’t want any more” movement.
The males made nests exactly like the females, but shallower, and they left them to search for their mates, leaving the ends open. On finding a female nest, they “serenaded” by tapping with their palps, and after some delay, tore open the web and entered. By and by the female came up and repaired the rent, first pulling the edges together with her jaws and then uniting them with silk from her spinnerets. In one case nothing more was seen of the male for nine months, when his empty skin was observed at the end of the tube. After nine months of connubial bliss his consort had devoured him!
In the autumn and spring, eggs and newly-hatched young were often found in the nests. Late in March a small hole, 1/16 inch in diameter, was noticed at the end of some of the webs, and presently the young began to emerge—never to return to the nest. They immediately climbed the highest objects at hand, and some were seen to be carried off by the breeze.
Enock found, by an ingenious experiment, that the sand which is incorporated in the aerial part of the tube—no doubt to render it inconspicuous—is obtained from within, and not from outside the nest. Carefully covering the exposed web, he powdered the ground all round it with red brick-dust, but the particles which the spider embedded in the web wereof brown sand, evidently obtained from the bottom of the burrow and not from the surrounding surface. But in the case of some newly-dispersed young spiders he was able to see this operation performed. The first part of the nest to be made was the aërial portion, at the foot of which the digging was commenced. Particles of sand were brought up in the jaws of the young spider and pushed into the weft of the tube. Occasionally the jaws were thrust through the delicate web and particles from without were seized andpulledinto the silken fabric.
It is sad to have to relate that such young spiders as did not emerge from the web within a reasonable time were devoured by their unnatural parent. It sometimes happened that a change of weather rendered it unsuitable for the departure of the young, and in this case the mother closed up the exit-hole, and retired to feed upon her offspring! Thus, though there were as many as a hundred and forty in a brood, a good many perished at the outset, and the ants in the surrounding soil accounted for some of the rest.
The Atypidae form a small outlying group of the Theraphosid spiders and are able to live in colder regions than most of their relatives. The great bulk of the division belong to the family Aviculariidae.
Some of the Aviculariidae are not unlike Agelena in their mode of life, spinning a dense sheet-webterminating in a tube, and entrapping their prey. Far the greater number, however, as far as their habits are known at all, are earth dwellers, either inhabiting more or less complex burrows of their own, or sheltering under stones or in chance cavities by day and emerging at night to seek food in the immediate neighbourhood of their hiding-places. Some of them are quite small, but the majority are large robust spiders, of formidable appearance. The largest known spider,Theraphosa leblondi, is found in South America, and its body measures more than three and a half inches in length. Few spiders have attracted more attention than the fabricators of the curious “trap-door” nests, which are common in the Riviera, and indeed in all the countries bordering the Mediterranean. But abundant though they are, they are extremely difficult to find, and it is generally only by chance that their existence is detected.
The Tarantula occasionally closes the mouth of her tunnel with a sheet of silk in which are encrusted thedébrisof insects or particles of soil. She does this at the time when she is spinning her cocoon and any intrusion is particularly inopportune, but she does it also on other occasions which are not so easily accounted for. A reason which would naturally occur to us would be the exclusion of excessive rain or excessive sunshine, but the facts, unfortunately, do not accord with this explanation.
Now, however desirable occasional closure may be, a permanent door would hamper the tarantula in her hunting operations, but the habits of the trap-door spider are different, and she closes her retreat with a wonderful hinged lid or “trap-door.” And the commonest form of trap-door is also the most perfect, being thick and tapering, and fitting accurately into the bevelled mouth of the tube like a stopper in the mouth of a bottle. It is made of alternate layers of spider silk and earth, and is free for more than half its circumference, the remaining portion of the surface disc being attached to the side of the tube by a flexible hinge of silk. Moggridge dissected the door of a full-sized tunnel into fourteen graduated discs. The smallest—and of course the lowest—represented the first door ever made by the spider, and the successively larger discs indicated the stages at which its increasing size rendered an enlargement of the tube—and therefore of the door—necessary.
The spider always interweaves vegetable matter from the neighbourhood into each new disc, so that, as a rule, it is entirely indistinguishable from its surroundings when closed; and not onlydeadvegetable matter, for if the tube is situated amongst moss, moss grows upon the lid. From our previous experience, however, we shall not be surprised to find that blind instinct and not forethought isresponsible for this action. Moggridge removed the lid of a tunnel and also cleared the ground immediately round it of all vegetation; nevertheless, when the spider made a new door, it covered it with moss taken from the undisturbed vegetation beyond, so that the trap-door was now conspicuous as a green oasis in a sandy desert! And on another occasion a spider interwove fragments of scarlet fabric left purposely at hand into the lid of its tunnel. It is clear, therefore, that the decoration of the door is due to an instinct which impels the spider to utilise any material of the neighbourhood without any regard to the effect produced.
The tube is densely lined with silk, which affords its architect a secure foot-hold, and if any enemy attempts to open the lid from without, the spider resists with all its strength—which is not inconsiderable—clinging on to its under surface with its front legs and jaws, while the claws of its other feet grasp the silken walls of the tube.
The other type of trap-door is less interesting and much more elementary, consisting simply of a wafer-like sheet of silk mixed with earth and vegetable matter, but it is a curious fact that while all known trap-door nests of the cork type are simple tubes, the burrows with wafer doors are often much more complex. In some cases there is a branch tube, like that constructed byLycosa picta, leaving the maintunnel at a depth of some three inches, and reaching the surface perhaps two inches away from the trap-door, so that the whole excavation isY-shaped. This branch tube is permanently closed by a thin sheet of silk and earth, which, however, it would not be difficult to break through if it were urgent for the spider to escape while the enemy was exploring the main tunnel.
But a more interesting case is the occurrence of another trap-door some way down the tube. If the tube is unbranched, this forms merely a second line of defence if the outer door is forced, but in the case of a branched tube the additional door hangs at the fork of theY, and is so shaped as to form a perfect valve, so that the spider, by holding it against one or the other side of the tunnel, can connect the bottom limb of theYwith either fork at will, leaving to the intruder a beautifully smooth-lined tube to explore, with no hint of the possibility of escape in other directions.
There are sometimes other complications in the ramification of the tube, but these need not detain us. Each species of spider adheres to its own particular type of architecture, and may safely—in a given neighbourhood—be identified by its nest.
As with the Lycosidae, the burrowing is all done by the mandibles, but here the first joint—the handle of the penknife—is of more importance than theblade or fang. Indeed the burrowing species of the Aviculariidae may be distinguished from the rest by their mandibles, which are provided in front with arastellum, or row of teeth for digging. A trap-door spider, then, does not go to work like a rabbit, or a terrier, scratching and kicking away the earth as it digs; it laboriously dislodges particles of soil with its powerful mandibles, and carries away the loosened fragments to deposit them at a distance.
The trap-door spiders of the Mediterranean region are nocturnal creatures, and little is known of their habits. Erber relates that a species found in the island of Tinos comes out at night, fixes open the trap-door with a few threads, and spins a web near its nest to entrap passing insects, clearing away any trace of it before the dawn. In the case of some Chinese and also some Australian species observers allege that they frequently wander from their nests in the day-time.
A Californian species was able to leave its nest when the trap-door was weighted with three ounces of lead. On re-entering, it seized the edge of the door with its mandibles, and, raising it slightly, inserted its front legs. It then turned round and slipped backwards into the tube. It always resisted the forcible opening of its door to the last moment, when it let go and slid into the tube “as though going down a well.”
The larger Aviculariidae have acquired a reputation for feeding on birds, and this has given rise both to their scientific and their popular name—bird-eating spiders. Several travellers have stated that they have observed them with birds in their grasp, and there is no doubt of their ability to kill any small bird or mammal, though it is probable that they seldom have the opportunity, for they spin no snare in which birds may be caught. Even without the aid of their poison, their jaws are so large and powerful that they may easily attain the vital organs of small animals. Probably their staple food consists of the larger insects.
They live in holes in the ground or in trees, or sometimes in the fork of a tree-branch. In such hiding places they spend the hours of day-light, emerging at night in search of food. Their large size and uncanny appearance have attracted the attention of the collector, and a great many species are known, but the fact that they chiefly inhabit tropical countries has militated against any very extended study of their habits, and the few items of information we possess are best related with regard to the particular spider observed, and not taken as necessarily characteristic of the whole tribe. There is little doubt that they live for several years. McCook kept a specimen ofDugesiella hentziin captivity for five and a half years, and he considered thatwhen it reached him it was at least a year and a half old, and probably more. The same species has recently been made the subject of some very interesting observations by Petrunkewitch, who obtained numerous living specimens from Texas and kept them in captivity; unless carefully packed, they bore the railway journey badly, and it was above all things necessary to supply them with water.
The captives were fed on grass-hoppers, crickets, cockroaches and wolf-spiders, but they ate sparingly, one grass-hopper sufficing for three days in the summer, while in the winter hardly any food at all was taken.
The sense of touch is extremely well developed in these spiders, but in sight, hearing and smell they are strangely deficient. No response whatever, was obtained to either high or low notes. A cricket sang for hours quite close to a spider which had been kept hungry for several days, without attracting any attention. It is very remarkable, by the way, that insects show no instinctive dread of these formidable creatures, not attempting to keep at a distance, and indeed frequently running over them in trying to find a way out of the cage. Nor do the spiders seem to be at all guided by smell; they evince no knowledge of the presence of insects which emit a strong odour, nor do they react to such tests as those to which the garden-spider was subjected unless strongirritants such as chlorine are employed, in the perception of which it is perhaps unnecessary that smell in the strict sense should take any part.
They have eight eyes—two of them round and rather business-like in appearance, and the others oval or pear-shaped—and they are very sensitive to light, retreating at once from the direct rays of the sun or from a light flashed on them, but they do not appear toseeanything at all, recognising neither friends nor enemies by sight, however close at hand. It was far otherwise with a wolf-spider in the same cage. Running towards the Dugesiella it was clearly aware of it at a distance of several inches, and could not be persuaded to approach nearer. But the supremacy of the sense of touch is most striking when the spiders are courting. When the male is seeking the female he seems quite unaware of her proximity unless he accidentally brushes up against her. If he loses contact for a moment he is quite at sea and wanders blindly about, turning, perhaps, to the left when the least motion to the right would bring them together again. This frequently happens when he has accidentally touched the female with one of the hind legs. He immediately turns about, and if she is still there, all is well, but if she has chanced to move out of reach, he is quite at a loss. Neither sight nor sound nor smell guide him, but touch only. The delicacy of this sense, however, is quiteremarkable. He seems to be aware at once of the nature of the object which touches him, assuming a threatening attitude if the touch is hostile, or pouncing instantly if hungry and the touch is that of a passing insect. If, however, the insect is lucky enough to escape, it is in no danger of pursuit.
As in the case of many spiders—though by no means of all—his courting is not unattended with peril. The tragic fate which sometimes overtakes the male spider has so hit the popular imagination that there is a general impression that the female spider is a confirmed misanthrope and desires the life of any suitor bold enough to approach her. Not at all! We have simply to remember that spiders are carnivorous and prone to cannibalism. If the female happens to be hungry she makes no nice discrimination between an amorous male and a succulent grass-hopper; if replete, she may find time for the play of softer emotions. The male ofD. hentziappears to be more or less prepared for a hostile reception on the part of the female, for the thighs of his front legs are furnished with spurs at their extremity and with these he holds back and renders powerless her threatening fangs.
There is no doubt that the spider’s delicate sense of touch resides in the hairs with which both body and limbs are thickly clothed. They are of various kinds—fine hairs, bristles, and stout spines—andmany of them are supplied with nerve-fibres at the base. The finer hairs are probably not sensory, and they are, in the case of some Avicularid spiders very easily shed, and have a strongly irritant action on the hand that touches them, not unlike the sting of a nettle.
It is not at all unusual for one large Avicularid spider,Psalmopoeus cambridgii, to be brought over to England in cases of bananas from the W. Indies. Mr James Adams of Dunfermline has kept two specimens alive for a considerable time. The first specimen lived in captivity for two years and nine months, during which it moulted five times but grew very little in size. Arriving in September, it was at first fed on flies, and in a few weeks, when these began to fail, it accepted beetles, consuming about three a day. In November, even these insects were difficult to obtain, and recourse was had to cockroaches. At first about three cockroaches a week were eaten but the number decreased until, in the middle of March it ceased feeding altogether, and on April 13 it cast its skin. It moulted again in October, and twice a year for the rest of its life—in spring and autumn. During six months it took no food at all, and very little for four months previously. At the last moult but one it lost a limb, which however, reappeared when the spider again changed its skin, though it never attained the proper size.
With spiders, as with insects, moulting is a very serious matter, involving much more than the mere casting off of an external coat. If all does not go well limbs may easily be lost in the operation, nor is it rare to meet with instances in which the animal has perished in its unsuccessful attempt to discard the old integument.
Mr Adams’ second specimen was kept alive for three years and ten months. It moulted only once each year—in June or July—and it died in the act of casting its skin. In the case of these spiders, also, it was noted that insects supplied to them as food displayed no fear whatever. There were always a few cockroaches in the same box, and they were often observed actually with the spider in its nest, but no notice was taken of them unless their host chanced to be hungry. A photograph of this spider is given in the Frontispiece.
It is an interesting fact that many of the Aviculariidae of Southern Asia and Australia possess a sound-producing apparatus which is entirely lacking in African and American forms, but this is a subject which deserves a chapter to itself.
STRIDULATION
Manyof the Arthropoda—the large group which includes insects and crustaceans as well as Arachnida—are able to produce sounds, a fact familiar enough in such insects as crickets and grass-hoppers. As, however, the breathing apparatus of these animals is entirely different from that of mammals and has no connection whatever with the mouth and alimentary canal, the mode of sound production is not at all the same. Instead of setting vocal chords in vibration by the expulsion of air through the larynx, insects “sing” or “chirp” by rapidly rubbing together certain specially roughened surfaces, which constitute what is called a “stridulating organ.” In crickets, for instance, each tegmen or wing-cover is provided with a kind of file, and when the wing-covers are rapidly vibrated, the edge of each rubs against the opposite file, and a loud shrill sound is produced.
The stridulating apparatus is by no means always in the same place; the thorax may rub against the abdomen, the leg against the wing-cover, or one of the mouth appendages against another. Nor are the sounds produced always audible to human ears;at all events there are many creatures with what appear to be very well developed stridulating organs whose note has never yet been heard by any naturalist, but there are doubtless numberless sounds beyond the range of our hearing, which is limited, like the keyboard of a piano.
Now such a stridulating apparatus has been detected in many spiders, and always in one of three situations—either between the two parts of the body (cephalothorax and abdomen) or between the palps and the mandibles, or between the palps and the front legs. In some of the Theridiidae the hind end of the cephalothorax is roughened and fits into a sort of socket in the abdomen which is provided with parallel ridges, so that when the abdomen is vibrated the two surfaces are rubbed together, but no one has yet heard a sound produced by these spiders. The stridulating Aviculariidae, however, are easily heard, the sound in some cases being described as a kind of whistle,—in others it has been said to have the effect of shot dropping upon a plate.
There are two quite distinct purposes for which sounds may be produced; they may either serve as a call from one sex to the other, or as a warning to intruders. Obviously the first purpose requires a sense of hearing in the sex appealed to, and it is interesting to note that in the Theridiidae, which are among the spiders which show some appreciation ofsound, the organ is well developed in the male only, being rudimentary or altogether absent in the female, while in the Aviculariidae, which appear to be quite deaf, both sexes possess it equally. In them its function is probably to warn off its enemies—a purpose for which it is not at all necessary that the spider itself should hear it.
Sometimes sounds have been quite wrongly attributed to spiders; there is, for example, an Australian species widely known among natives as the “barking” or “booming” spider, for no better reason than that the spider has been found in the day-time at a spot where the booming was heard at night. This case was investigated by Professor Baldwin Spencer, who found that quails were really responsible for the sounds with which the spider was credited. The creature could, however, achieve a kind of whistle by rubbing its palps against its mandibles. Its stridulating apparatus was of the type common among the Aviculariidae. Its principle is that of the musical box, where nail-like projections on a barrel strike against the teeth of a metal comb, except that the barrel is stationary and the comb is moved up and down against it. The barrel is here represented by the first joint of the mandible which is beset on its outer side with spines. The inner edge of the first joint of the palp is furnished with “keys” which are rubbed against the mandible spines when the palpsare vibrated. These keys are very curious structures. They are of various lengths, and their shape will perhaps be understood when it is said that a tolerable model of one would be obtained by taking a flat iron bar, sharpening it at the end, and then so twisting it in the middle that the flat surface of one half is at right-angles to the flat surface of the other half. Its appearance therefore varies according to the point of view, the narrow edge of one half and the broad edge of the other being visible at the same time. A moment’s consideration will show that this torsion is calculated to give great rigidity to the keys, for when the outer half is struck on the flat surface the inner half opposes its greatest diameter to the shock. A similar structure is found in all the Theraphosid spiders which are ableto produce a sound, though sometimes the “keys” are on the mandibles and the spines on the palp.
Fig. 11. Three “keys” of a stridulating organ, after Spencer.Fig. 11. Three “keys” of a stridulating organ, after Spencer.
Fig. 11. Three “keys” of a stridulating organ, after Spencer.
In Staten Island there is a wolf-spider—Lycosa kochi—which is known as the “purring” or “drumming” spider because of a curious habit which the male has, at mating time, of rapidly drumming on the dead leaves in a wood with its palps. It runs hither and thither over the ground as if in search of something, pausing at short intervals to “purr,” and the sound had frequently been heard and correctly attributed to the spider before the way in which it is produced was discovered. In this case it is probable that the production of sound is not the object of the spider at all, for we have no evidence that wolf-spiders hear. On the other hand rapid tapping with the palps is a very characteristic action with male spiders at mating time, and it is easy to believe that contiguous dry leaves would conduct vibrations to a female at some distance away and inform her of the presence of the male. Just so, as we have seen, our English Theraphosid announces his arrival by tapping on the exposed part of the nest of the female.
THE SPINNING APPARATUS, AND THE FEET
Seeingthat the possession of spinnerets is a characteristic of all spiders, and that a great deal of the interest attaching to their life-history arises from their spinning operations, any account of the group, however brief, would be incomplete without some attempt to describe these remarkable organs.
Among the spiders to which the attention of the reader has been directed, some have been highly accomplished spinners, constructing complicated snares, retreats and egg-cocoons, while in the case of others the spinning work is very meagre and employed chiefly for the protection of the eggs. As might be expected, the organs attain a very much higher development in some spiders than in others, and the most complex of all are those of the Epeiridae, the constructors of the circular snare.
Now in the first place it is rather striking that the spiders with the most conspicuous spinnerets are by no means the most able spinners. The “bird-eating” spiders are a case in point, for they spin very little, yet two of their spinnerets are much more obvious than anything Epeira has to show, for they protrude behind the body and strike the eye at the firstglance. Indeed excessive length has nothing to do with complexity but is found wherever a wide sweep is necessary in laying down the threads—as we saw in the case of Agelena, when constructing its sheet-web.
Roughly speaking, the spinnerets are very mobile finger-like projections, generally situated under the hind end of the abdomen and, bearing more or less numerous tubes from which the silken threads proceed. The usual number of spinnerets is six, but there is a pretty wide range, one group of spiders having only two, while a few possess eight.
The spinnerets, then, are only the bearers of the actual tubes which emit the silk. The distribution of the tubes themselves is different in the different kinds of spiders, but it is usually possible to distinguish two kinds. There are generally present a large number of very fine cylindrical tubes or “spools” and a few conical tubes of much larger base, which are called spigots. Each of these orifices, whether on spool or spigot, is connected by a fine tube with a separate silk gland, or organ for manufacturing silk, situated within the spider’s abdomen. Epeira has about 600 of such glands, each with its own terminal spool or spigot, and the large number of these tubes has given rise to a misconception that is very widely spread—namely that the spider’s line, fine as it is, is “woven” of hundreds of threads of very much finer silk. This is not so, as we shall presently see.
Though Epeira has some 600 silk-glands, it has only five differentkindsof gland, manufacturing silk of different properties. No other family of spiders has so many, though two other kinds of gland have been found in less elaborate spinners. Within the spider the silk is fluid but it solidifies on meeting the air, each thread hardening as it emerges though still continuous with the fluid contents of the gland, so that the drawing out of a silken thread is just like the operation so familiar with the glue-pot, or with spun glass, except that the hardening is not due to cooling but to exposure to the air. This general description will, it is hoped, make an account of the organs in Epeira more comprehensible.
The spinnerets of Epeira are so small and inconspicuous that their disposition is not very easy to make out. When not in use they form a tiny cone under the tip of the abdomen, and only four are visible, their free ends being so brought together as entirely to conceal a small central pair. There are really, then, three pairs of spinnerets which we may call at once the anterior, median and posterior pairs, though when at rest only the anteriors and posteriors can be seen. If the spider is observed with a pocket-lens as it crawls about in a glass tube it will be noticed that the spinnerets are capable of great mobility. Their ends can be separated or brought together, or they may be made to rub against eachother or against the sides of the tube. The anteriors and posteriors, moreover, are two-jointed though the medians consist only of a single joint.
So much can be seen without any great magnification, but the microscope will be necessary if a complete understanding of their mechanism is to be arrived at. What it reveals will now be briefly described, and will, it is hoped, be made tolerably clear by the accompanying figures which are simplified by the omission of a large number of bristles which tend to hide the essential structure, and by a great reduction in the number of “spools,” though the spigots are all indicated.
The anterior spinneret (that nearest the head end of the animal) is a sort of cone, divided into a large basal joint and a small terminal joint. The latter bears on its inner side a single spigot (fig. 12a) and is crowned with a battery of spools, about a hundred in number.
The median spinneret has three spigots, two at the tip and one on the inner side (fig. 12b), and about a hundred spools, mostly on its inner surface.
The posterior spinneret is divided very obliquely into two joints, so that the terminal joint extends much lower down on the inner than on the outer side. It has five spigots in groups of three and two, and again there are about a hundred spools.
Now the point that I wish to make clear is thatthere is no interweaving of the output of these various spools and spigots. At the moment of emission the threads are adhesive, and can be made to stick to the glass or to one another, but they are not in any sense either fused or interwoven. For ordinary operations the brunt of the work is borne by the spigots markedain the figure, sometimes reinforced by silk from the spigots on the median spinnerets markedb, the functions of all the other spools and spigots being special and occasional. For instance, when Epeira is laying down a foundation line, this is what happens. The spider sits down, so to speak, on a twig, separating its spinnerets and rubbing them on the surface. As it raises its abdomen a multitude of little threads are seen merging into what appears to be a single line.