Fig. 57.—A Larva Glass.
Fig. 58.—A Larva Glass.
If you find it necessary to move the larvæ yourself from the stale food, never touch them with your fingers, but lift them gently by means of a small camel-hair brush. Larger larvæ need never be moved at all. They will always search out fresh food for themselves, and the stale may be removed after they have quitted it.
For rearing larger species ordinary bottles are hardly satisfactory, and we must either use large jars or construct cages of some kind.
An ordinary bell jar such as is used for covering ferns or for aquaria makes a very useful 'larva glass.' Place a small bottle of water at the bottom, and then introduce sufficient dry clean sand or sifted soil to reach up to its neck. On the top of this place a layer of moss or cocoa-nut fibre. Next introduce the food plant, fixing it firmly in the bottle of water, and plugging up the space betweenthe stem and the rim with cotton wool. This precaution is to prevent the larvæ from falling into the water as they attempt to pass up or down the stem, and the wool also helps to keep the twig in a vertical position. The glass is now ready for the caterpillars, but it is advisable to keep a covering of muslin or gauze over the top in all cases even though the larvæ contained are unable to creep up the surface of glass, for the great enemies of caterpillars—the ichneumon flies—are always on the alert, and will often take advantage of an open window to 'sting' the larva rearer's pets.
Another form of larva glass can easily be made out of a large glass jar if you know how to cut off the bottom, or of a chemist's bell jar which is open both at top and bottom. In this case the bottle of water and the soil are arranged as before in a pan of unglazed earthenware, and then covered over with the glass. This is shown infig. 58, and is an exceedingly convenient larva house, since the lifting of the glass enables you to get at the insects without any trouble.
Fig. 59.—A Larva Cage.
Wood larva cages are very commonly used for the larger species after they have attained a fair size and require more food than can be stocked in bottles and glasses. These cages have glass fronts, either sliding or in the form of a hinged door, and sides of perforated zinc. They are kept in stock by all dealers in entomologists' requisites, but equally useful ones are easily constructed. If you select a box of suitable size at the grocer's, cut out large pieces from the lid and sides with a fret saw, and fix in the glass and zinc, you will have a cage that will answer all purposes.
The internal arrangements consist of a shallow tray filled with soil, in which stands the bottle of water for the food, and a layer of moss sufficiently high to cover the bottle completely.
A series of such boxes standing on end on a shelf, or hanging on a wall, will form a very satisfactory nursery for your pets, and will occupy but little space.
We have already observed that some larvæ burrow into soil when about to change, while others creep to a sheltered corner, orsuspend themselves from the food plant itself. It will be seen that the larva cage just described supplies all these demands, and care must be taken not to disturb the occupants while they are undergoing their metamorphoses. Those that suspend themselves on the food plant should be allowed to remain where they have fixed themselves, and when it is necessary to remove the stale food in order to give a fresh supply to the later larvæ, let it be fixed in an airy place where it can be watched till the perfect insects emerge. Those which suspend themselves on the sides or top of the cage, or spin cocoons in the corners, should never be disturbed unless you are greatly in want of the same cage for the accommodation of another brood; and even then it is possible that their presence will not in any way interfere with the new species. But if their removal becomes a necessity, let it be carried out as carefully as possible, and not until the change to the pupal stage is known to be complete.
The species that burrow into the soil or bury themselves in the moss need never be disturbed till the rearing season is quite over, and then they may be transferred to a box specially kept for the accommodation of pupæ.
There is yet another method of rearing larvæ to which we must refer—a method known as 'sleeving'—particularly useful when you happen to have the required food plants in your own garden. The ova or larvæ are placed on the plant, the whole or part of which is then covered with a bag or 'sleeve' of gauze. The larvæ thus imprisoned have the full benefit of fresh air and light, and are also free from the attacks of ichneumon flies. They have a fair amount of liberty, and yet cannot get beyond your reach; also abundance of fresh food without further trouble on the part of the rearer.
But even this arrangement is not perfection. It will not suit the night feeders that like to hide beneath the soil during the day, and it interferes somewhat with the burrowing tendencies of those which pupate underground. These little difficulties, however, can be overcome by placing the food plants in large pots or tubs of soil, and tying the mouth of the 'sleeve' round the outside of this utensil. If this cannot be done, those insects that pupate underground must be removed from the plant when their restless disposition shows that the changing time has arrived, and then be transferred to a box of soil where they can find the seclusion they seek.
The larvæ that hybernate throughout the winter are rathermore troublesome, especially those which are inclined to take a ramble on certain mild days in search of food when none is at hand. Still there is no reason why even a beginner should not attempt the rearing of these. They will require food in the autumn until the cold weather sets in, and again early in spring as soon as the new leaves appear; but this is not of much consequence to those who reside in districts where the required food plants abound.
Wood feeders also require some special treatment and precautions, and the successful rearing of some is a matter of no little difficulty. A wooden cage is, of course, quite out of the question with these, unless you wish to test the power of their jaws. They must be kept in large pots or jars, covered over with wire gauze or perforated zinc, and supplied with fresh stems or logs of wood, or with moist sawdust fresh from their favourite tree. A few of them—the 'Goat' (page 224), for example—will eat dead and rotting wood, and may be fed on old palings and other waste providing the right kind is selected.
The troubles and disappointments of larva rearers are numerous and varied, and commence with the earliest moments of the young insects. Even the hatching period sometimes proves a trial, for it occasionally happens that the young larva has not sufficient strength to bite its way through the shell that surrounds it, and dies with nothing but the surface of its head exposed to view. This may be the result of keeping the ova in too dry a spot, the shell having become too hard and horny for the little creature's jaws.
Then the moulting seasons are always periods of trial to the larvæ, and often of loss to the rearer. Some of the hardier species may pass through all their moults without appearing to suffer anything more than a slight inconvenience at each, but in other cases the greater part of a brood may fall victims to these ailments of the growing stage.
Apart from these sources of loss, however, larvæ are subject to numerous diseases, infectious and otherwise, about which we know but little. A fever may rage in one of our cages; a fungoid growth may establish itself on the bodies of our pets, or we may see them cut down, one by one, through a fatal attack of diarrhœa.
In many such cases we are at a loss as to what to do. Blue pills and black draughts are not to be prescribed, and the modern practices of surgery and inoculation have not yet been applied toinsect patients with very great success; but we must do our best to adopt hygienic principles, paying the greatest attention to proper means of ventilation and to a regular and wholesome dieting. In the case of diarrhœa—a very common insect malady—the best we can do is to avoid the young and juicy leaves of the food plant, and substitute the older, and drier foliage.
Ichneumon flies have already been mentioned as great enemies of larvæ. These flies either deposit their eggs on the skins of caterpillars, or thrust their sharpovipositorsinto the creature's flesh and lay their eggs beneath the skin. When the young ichneumons are hatched, they immediately begin to feed on the fatty matter that is usually stored in comparative abundance under the skin of the caterpillar, and thus they grow at the expense of their host, within whose body they lie completely hidden from view.
The poor caterpillar, though being eaten alive, often shows no external signs of the mischief wrought within, and, even though its substance is really decreased by the hungry internal parasites, yet the rapid growth of these robbers maintains the general plumpness of a healthy larva. But the ichneumons, having at last devoured the store of fat, and avoided the vital organs of the caterpillar, as if with a view to preserve their living home to the latest moment, now commence to attack the latter, speedily reducing the vitality of their host to the lowest ebb, and finally causing its death.
This untimely end may come before the caterpillar is full grown, or the insect may change to the pupa before the ichneumons have done their worst, but it rarely occurs that the unfortunate creature has sufficient strength to carry it on to the final stage.
A large number of the collected larvæ will have been 'stung,' much to the disgust and disappointment of the rearer; and hence the advantage of rearing your specimens from ova wherever possible, providing you keep them so well under cover that the ichneumons cannot visit your broods.
The disappointments connected with the rearing ofLepidopteraare by no means at an end when all have passed successfully into the pupal condition, and the number of perfect insects obtained will often fall far short of the number of pupæ in your boxes; butwe must now see what can be done to minimise the death rate of the captives.
One or more suitable boxes must be prepared for the reception of the pupæ, and the following suggestion will answer all purposes:
Get a wooden box, quite rough and unplaned inside, large enough to accommodate your pupæ with ease, and not less than eight inches deep. Make several holes in the bottom, or else knock the bottom completely out, and nail in its place a sheet of perforated zinc. Also make a lid consisting of gauze attached to a light wood frame.
Place a layer of clean gravel, about an inch deep, in the bottom, and over this a few inches of sifted soil or cocoa-nut fibre.
Now take all the pupæ that are 'earthed' in your cages, and arrange them on the prepared bed; also add to them the pupæ you may have dug out during your various excursions. Cover all with a layer of the material selected for the bed, and then add a layer of moss.
Next come the pupæ that are suspended by silky fibres, or are inclosed in cocoons. These should be fixed with pins around the sides of the box, running the pins either through the tuft of silk at the 'tail,' or the outer layer of the cocoon, or through the portion of the dried food plant to which they are attached.
Here your pupæ will remain till they emerge, and the box may be kept in any airy place where it is not likely to be forgotten, for it is essential that the perfect insects should be removed as soon as possible after quitting their cases. It does not matter much whether the pupæ be kept in or out of doors, providing they are sheltered from rain and very severe frosts; but of course, if the former, the imagines will emerge a little earlier, even if the room in which your specimens are stored has no fire.
Even when protected in boxes such as that described the pupæ are subject to enemies and dangers. The soil and moss employed may contain slugs, mites, or other creatures which prey on insects, and the amount of moisture present in these materials and in the atmosphere may prove too little for some species or too much for others.
The remedy for the former evil is a simple one. Bake the soil or fibre well before fitting up the box, and boil and afterwards dry the moss. You may then be sure that all life previously contained is quite destroyed.
But the degree of humidity is a point not so easily settled, and so variable are the experiences and opinions of different entomologists that it is difficult to advise a beginner on the subject. The fact that some strongly advise a perennial dampness, while others recommend no attempt at the application of water, would seem to show that there are probably important points to be urged on both sides.
Nothing can be better than a very careful observation of pupæ in their natural conditions. When engaged in pupa digging you will observe that the larger number are to be found on the east and north sides of trees where the soil is protected from the heaviest rains; on the other hand a good many are certainly found in very moist and sometimes even in wet situations.
Particular notice should be taken of such experiences, making every allowance for the exceptions that prove the rule, and then let the natural conditions be maintained in your nurseries at home. To carry this out two pupa boxes should be kept, one for those species that seem to require dry situations, and the other for the species that apparently do best with moist surroundings.
But when it is desired to maintain the pupæ in a moist condition, great care must be taken not to allow any accumulation of stagnant water. The box we have described, with its bottom of perforated zinc, is well adapted for this purpose. Let it stand on a couple of strips of wood, so that any excess of moisture may readily drain through. The perforated bottom will also allow of a free circulation of air, thus securing the ventilation that is desirable in all boxes, whether wet or dry.
If you have any insects that have pupated within moist stems, they should be kept in a moist condition till they emerge. The simplest way of doing this is to support the stems in a layer of wetted but well-drained silver sand.
Forcing may be resorted to when it is required to obtain the imagines for early setting in order to get them in the cabinet before the busy season begins. The method is simple. Place the pupa box on a shelf in a room where a fire is kept every day. By this means you may get all your specimens out within a few weeks, even when you start the forcing at the beginning or middle of the winter. If, however, you require the imagines for breeding, you must be careful that the eggs are not laid long before the buds of the necessary food plants are due.
When you are expecting the appearance of perfect insects, thepupa boxes should be examined every day. A morning visit to your pupæ (for most insects emerge in the morning) may reward you with the sight of a newly emerged imago, clinging to the rough surface of the box, thus affording you an opportunity of observing the wonderful expansion of the wings. But the greeting is not always of such a pleasant character, for your disappointed eyes will sometimes be cast on a host of horrid ichneumons that have just quitted a shell from which you were expecting a prize of some specially valued species.
Up to the present we have been dealing only with living forms—learning how to catch and rear the Lepidoptera that fall to our lot; but now we have to become acquainted with the methods of preparing our dead specimens in such a way that they may form a useful collection for future study and reference. Our first attention shall be given to the apparatus necessary for this work.
The most important requirement is the setting boards, of which several are necessary, the sizes varying according to the dimensions of the different insects to be 'set.' Thelengthsof all the boards should be the same, not only for the convenience of packing when not in use, but also in order that they may, if required, be arranged neatly in the 'drying house' to be presently described. The widths only will vary, and in this respect the boards must be adapted to the measurements of the insects from tip to tip when the wings are fully expanded. Thus, a set of a dozen boards, ten or twelve inches long, and from one to five inches wide, will do for a good start. Of course you may commence with a smaller number than twelve, but if you really mean to do the thing well, you will eventually require a good stock of boards.
Here, again, it may be mentioned that all the necessary requisites may be purchased ready for use, a set of boards and a drying house complete costing from ten to twenty shillings according to size and quality; but as the reader, like myself, may prefer to construct his own, I will supply him with hints and suggestions sufficient for the work.
Each board is constructed in this way. Cut out and plane up a piece of wood of the required length and breadth, and about one-eighth of an inch thick. Glue on the top of this a layer of corkabout half an inch in thickness, leaving the whole under a moderate pressure until the glue is quite hard. The sheets of cork for this purpose may be bought at any naturalist's stores; but slices cut from good large bottle corks may be made to answer equally well if you don't mind the extra time expended in cutting and fixing.
When the glue has well set, trim off the edges of the cork flush with the sides of the wood, and then cut out a groove down the whole length of the cork, of course in the middle, and of such a size that it will just contain the bodies of the insects for which it is intended.
Fig. 60.—Section of a Setting Board.
The satisfactory cutting of this groove is not a very easy matter, but if its position is first carefully marked, a long rat-tail file may be made to plough it out neatly and regularly. As an alternative the following plan is good. First cover the wood with a layer of cork about aquarterof an inch thick, and then glue on the top of thistwonarrower strips, about as thick as the bodies of the insects for which the board is intended, leaving a space of the required size between them, as shown infig. 60. In this way you get a groove of square section, that is in some respects preferable to the round one cut out by means of the rat-tail file.
Fig. 61.—Sections of Setting Boards.
Now comes a question about which there is a difference in the tastes or fancies of entomologists. Shall the boards be perfectly flat on the top, or shall the sides slope from the groove, or shall the surface be rounded? A glance at the three sections of setting boards will show clearly what is meant. The rounded board is most commonly used, and the graceful curve thus given to a butterfly or moth set on such is certainly attractive; but it is not natural. The wings of these insects are rigid, and are never seen bent into such curves in a living specimen. For this reason I much prefer a perfectly plane surface on each side of the groove.Then, as to whether there shall be a slope or not, this is a matter of less importance. A very decided sloping of the wings is certainly not so convenient for future examination; nor does it, to my mind, look nearly so well as both sides in the same plane, or at a very gentle inclination. But perhaps this subject had better be left to the taste of the reader, remembering, however, that, whatever plan be adopted, all the boards should be alike in this respect, so that there may be a degree of uniformity in the cabinet.
The surface of the cork must, in all cases, be nicely smoothed down with glass paper, and then covered with thin white paper, fixed to its surface with ordinary paste.
When insects are on the boards, they should be placed in an airy spot, as free as possible from dust, while they are drying. Hence the advisability of some form of 'drying house.' This is simply a box, standing on end, and provided with a hinged door consisting of a sheet of perforated zinc in a wooden frame. The boards may slide in this on little slips of wood nailed or glued on to the sides, or the wooden bases of the boards may project beyond the cork at the ends, and slide into grooves in the side of the house.
Fig. 62.—A Butterfly on the Setting Board.
Beyond these requirements nothing is wanted save a good stock of pins, thin card or ordinary writing paper, and a 'setting needle.' The last-named item is simply a needle mounted in a handle, and a good one may be made by thrusting the head of a darning needle into a piece of twig. The pins used for setting—that is, for fixing the pieces of paper or card to keep the parts in position—may be of the ordinary kind; but entomological pins are far preferable, even for this purpose; for, being much thinner, they do not damage and disfigure the setting boards so much.
Now as to the setting. First see that the pin with which you are to fix your dead insect passes centrally through the thorax. Then fix it firmly on the setting board, its body lying neatly in the groove of the cork. Cut out some little pointed strips of card or paper, and, after bringing the wings into position with the settingneedle, fix each one by a pinned strip. In spreading out the wings, care must be taken not to pierce them at all, but simply to push them into their place by pressing the needle at their bases, or by putting the needle beneath andliftingthem out.
Instead of pointed pieces of card, uniform strips of paper may be used, as shown infig. 63, each strip passing over both wings.
After the four wings have been properly arranged, a few extra pins may be used to keep other parts in position. Thus, the antennæ may be placed at equal angles, the proboscis may be extended, and a couple of pins may be used to support the abdomen if it is inclined to bend downward.
Fig. 63.—Another Method of Setting Butterflies and Moths.
As before mentioned, insects should be set soon after they are dead, while the parts are still soft and supple. But where this cannot be done, and the specimens have become stiff, brittle, and rigid, they must be 'relaxed' before any attempt is made at setting them out.
This process of relaxing consists in placing the specimens in a very moist atmosphere for a few days. There are several simple ways of doing this, many of which will readily suggest themselves to the reader. Your collecting box, if a zinc one, may also be used as a relaxer. Pin your stiff insects in it, after well moistening the cork, and simply shut them up for a day or two. Any metal box will serve the same purpose providing you put into it a piece of sheet cork on which to fix the insects, and this cork may rest on a bed of moist sand.
Another plan is to float the pinned specimens on corks in a shallow vessel of water, and cover them over with a bell glass.
Insects that are being relaxed should be examined from time to time, and the degree of flexibility acquired tested by a gentlepressure of the setting needle or by blowing on them. If not sufficiently supple, give another day in the damp cell, but never allow them to be forgotten till they are covered with mildew.
The time occupied in thoroughly drying butterflies and moths will vary considerably according to their sizes and the condition of the atmosphere. In hot and dry summer weather four or five days will prove quite sufficient for theverysmall and thin-bodied species. From one to two weeks, however, may be looked upon as the average period; but the large and thick-bodied moths may require more than this.
Perhaps the best test of their condition is the gentle pressing of the setting needle against the abdomen—the last part of the body to become dry and stiff. If the abdomen seems quite firm and rigid, you are pretty safe in removing the specimen from the board; but if it bends at all under a slight pressure of the needle let it remain for a day or two longer.
If your cabinet is quite ready for the reception of new-comers, the insects may be put in their proper places immediately after their removal from the setting boards; but if not, they may be pinned temporarily in a 'store box' till the time comes when you have proper accommodation provided. The full consideration of these matters will be dealt with in another chapter.
It is possible that the setting of some of your specimens will not exactly please you. If such is the case, put them in a relaxing box for a day or two, and then reset them more to your fancy.
We have now to deal with a matter that applies more particularly to moths, especially the very large and thick-bodied species. The abdomens of these become more or less contracted and shrivelled on drying, sometimes to such an extent as to look most unsightly.
There is a remedy for this, and the time and patience required in working it out will be well repaid by the superior results obtained.
While the abdomen is still in a soft condition, make a slit throughout its length with a very sharp knife or a sharp-pointed pair of scissors. This slit should be made down the centre of the under surface, or, if the insect is to be placed in the cabinet with the under side exposed, down the middle line of the back. Then remove all the contents of the abdomen, scraping them out with a piece of hooked wire, or removing them with a fine pair of forceps, and leaving the skin as clean as possible both within and without.Now introduce a packing of cotton wool, just sufficient in quantity to maintain the natural form of the body as the specimen dries.
There is another good method of stuffing moths that possesses a decided advantage over the one just described, since it leaves the specimen in such a perfect condition that it shows no appearance of having been stuffed when viewed from either side. This consists in snipping off the abdomen at the waist, clearing out the contents with a hooked wire, lightly stuffing it with cotton wool pushed in at the waist, and then setting it aside to dry, while the other part of the insect is undergoing the same process on the setting board. When both parts of the moth are thoroughly dry, the stuffed abdomen is easily fixed in its place with a little coaguline; and this, if neatly done, will not show the slightest sign of the treatment to which the insect has been submitted.
Even after your insects are finally housed in the cabinet, they are subject to two other dangers, both of which are more destructive to moths than to butterflies. One is technically known as 'grease,' and the other is the invasion of certain museum pests that feed on the specimens, causing them to fall to pieces.
Examine the moths that have been for a time in the cabinet, and some are sure to exhibit an oily or greasy appearance, the hairs of the abdomen, and perhaps also of the thorax, being clogged together just as if the specimen had been dipped in oil, the same miserable condition perhaps being shared also by parts of the wings.
This is due to the gradual oozing out of the fatty matter that is always present to a greater or less extent in the bodies of the insects, and which must necessarily show itself more sparingly in specimens that have been carefully stuffed.
The old saying, 'Prevention is better than cure,' applies well in the present case; but as there are times when a knowledge of the 'cure' is the only means of saving a valuable specimen from destruction, we will study both.
To deal with the two in the order of the well-worn proverb, we will consider the prevention first. Always carefully clean out and stuff the abdomens of large-bodied insects; and as a rule, treat them with some substance that will either absorb or dissolve out all oily matter. I think the best plan is to remove the abdomen, clean it out if its size permits of such an operation, and then, after labelling it to prevent its future application to the wrong body, either let itremain in a bottle of magnesia for several weeks, or soak it in benzole or ether for a few hours or longer.
If magnesia has been employed as an absorbent, you have simply to blow or lightly brush off the loose powder that clings to the body, and then fix it in its place with coaguline. A body dipped in ether or benzole will look as if completely spoilt at first, for the furry coat that clothes it will lie matted and almost entirely robbed of its beautiful colours, reminding one forcibly of the proverbial 'drowned rat.' But take no notice of this change. Let the body have at least a few hours in the liquid, extending the time to a day or two in the case of very large ones and those which experience has proved to be particularly liable to 'grease;' and, immediately on withdrawing it, fix it with a pin in a good strong draught, such as you may obtain by opening a window about an inch, or, if a breezy day, in the open air.
These liquids are so volatile (and for that reason should never be left exposed in an open vessel) that they rapidly evaporate, leaving the dry hair to be loosened by the breeze, thus bringing back the natural appearance almost perfectly.
It is probable that many of the smaller insects that were not considered to require the stuffing or grease-removing operations will sooner or later exhibit a greasy tendency in the cabinet. At first the abdomen is affected, and the oily matter then gradually creeps over the rest of the body, finally spreading over the wings, and giving the insect a most deplorable aspect. But these are not irreparably lost, and the following cure will often bring them back to their former beauty.
If the abdomen only shows signs of grease, cut it off and soak it in one of the above-named liquids for a day or so, replacing it as above after the drying operation. If, however, the oily matter has spread to the thorax and the bases of the wings, the whole specimen must be soaked, using a basin or jar of suitable size, covered with a plate of glass. A good draught during the drying operation will do much to prevent the hair from sticking in matted tufts close against the surface of the body and wings, and a gentle brushing with a very soft camel-hair brush will loosen and reset the fur.
The other danger to which we have referred is the invasion of certain 'mites' and other museum pests that pay periodical visits to our cabinet drawers and store boxes, often committing such havoc as to severely try the patience of an interested naturalist.
The way to prevent such intrusions is to make the atmosphere of the compartments so obnoxious (to them) that they dare not enter; and, further, to so spice up your specimens that they are no longer safely edible to the invaders.
The first object can be attained by always keeping camphor or naphthaline (albo-carbon) in each division. A lump of either substance may be secured by pins or a little perforated cell in the corner of each drawer or box, or the bottom of each may be dusted with finely powdered naphthaline; but as both these solids are volatile, care must be taken to renew the supply as occasion requires.
Then, with regard to the second precaution, perhaps nothing is more effectual than corrosive sublimate. A little of this may be dissolved in a small bottle of alcohol (spirits of wine), labelled with the name and the wordPoison, and kept ready for use. All the skins of stuffed specimens should be painted with this solution, and the stuffing itself may be moistened with it before insertion.
There is yet another circumstance that renders a watchful care of your cabinet specimens necessary, if you happen to possess many that were captured 'at sugar.' Some of these will have so gorged themselves with syrup that they are literally full of it, and this will sometimes find its way to the outside, often dropping on the surface beneath. In such cases the sugar should be removed as completely as possible, and the bodies stuffed, before they are quite dry; but if the specimens have been in the cabinet so long that they are stiff and hard, the under sides of the abdomens may be completely cut out with a very sharp knife and thrown away, and then the sugar cleaned out from the upper shell as neatly as possible.
Many young entomologists give their attention almost solely to the perfect forms of insects, often collecting and studying a very large number of species without regard to their earlier stages and metamorphoses. This is decidedly a very great mistake. Although the lifeless form pinned in a cabinet may be a most beautiful object in itself, yet a study of this alone is uninteresting compared with that of the wonderful changes it has undergone since the time it was a very young larva.
The different stages of the insects should be known as far as possible, and these, as well as the perfect forms, should be included in the collection for future study and reference. A good cabinet, according to my own opinion, is one that possesses, among other good features, a number of complete sets illustrative of the life history of at least the more typical forms; and as it is not a difficult matter to preserve the earlier stages, there is really no excuse for their omission from the collection.
The empty shells of ova are in themselves sometimes interesting objects, especially when they illustrate some peculiar instinct on the part of the parent. Sterile eggs, also, often fall into the hands of breeders and rearers, and these, though in other respects unprofitable, are useful in the cabinet.
If fertile eggs are to be prepared for a collection, they must be killed. This is easily done by thrusting into each one the point of a very fine needle, or by immersing them for a moment in boiling water, or by shutting them up in a bottle with camphor. In drying they often contract more or less, and frequently change their colour; still these are useful, providing notes have been taken of the characters thus lost. The larger eggs are capable of special treatment where the owner has the necessary time and patience, and where the highest results are desired. By means of a surgeon'sinjector of small size the contents of the eggs can be removed; and then, by the same instrument, a warm solution of gelatine, coloured in such a way as to restore the natural tint, may be forced into the empty shell. As the gelatine cools and hardens, it prevents any shrinking of the shell, and thus both form and colour are well preserved.
For the preservation of larvæ you will require one or two simple appliances.
The first of these is a suitable glass blowpipe, one form of which is here illustrated. It consists of a glass tube, one end of which has been drawn out very fine; a piece of watch spring tied to it in such a manner that it will hold the skin of a larva at the small end, and a piece of india-rubber tubing at the other end, pressed by means of a brass spring clip.
Fig. 64.—A Blowpipe for Larvæ.
A little drying oven is also very useful, but not absolutely necessary. If you decide to have one, any square box of sheet iron (not soldered tinned iron) may be readily converted into one. It must be provided with a hinged door in the front with a ventilator at the bottom, a hole for the escape of hot air at the top, and a tripod wire stand inside on which to rest the specimens while drying. The whole should be supported on a wire stand, so that heat may be applied below.
Each larva to be preserved should be dealt with in this way. First kill it by means of any one of the killing bottles or boxes already described, or by immersion in spirit of wine. When quite dead, enlarge the anal orifice by thrusting a needle into it, and then lay it on a piece of blotting paper with its head toward you. Now take a round ruler, previously covered with blotting paper, and roll the larva gently from head to tail till all the contents of the skin have been expelled. Next fix the skin on the fine end of the blowpipe, by thrusting the point of the latter into the opening, and allowing the spring to press gently on its edge. Gently blow into the skin till it is inflated just to alittle belownatural size, theneither hold it near a fire or rest it in the drying oven till it is quite dry and rigid.
If you have done your work neatly, the skin and blowpipe will both be quite air-tight when the clip is closed; and the air, finding no outlet, will still further inflate the skin when it expands on exposure to heat. This is the reason why you are directed to blow it out to something short of the natural dimensions. If you find that this expansion causes the skin to stretch beyond its normal size, a little of the air must be allowed to escape while it is yet soft and flexible.
The front of the larva is generally the last portion to become dry, and when this is quite rigid the skin may be removed from the blowpipe. This is a matter that requires the greatest care; for the skin is so very thin and brittle that a little rough handling will break it to pieces. As a rule it may be easily pushed off the pipe by a slight pressure behind, or a gentle twisting motion will loosen its hold; but this latter method can hardly be applied to hairy larvæ without breaking off the hairs, now rendered very brittle by the heat.
If you find the slightest difficulty in detaching the skin of a valuable specimen, it is far better to damage the blowpipe than to risk spoiling the skin. Supposing your blowpipe is a glass one, you can easily break off the end of it after making a cut with a very small triangular file, and the portion thus removed may be left attached to the skin. Then, after softening the glass blowpipe in a gas flame or the flame of a spirit lamp, it can be drawn out thin again for future work. Those who can manipulate glass tubing in this way will find it far better to lay in a stock of suitable material, drawing it out when required, than to purchase blowpipes ready made at the naturalist's shop.
Very fine hollow stems, such as those of the bamboo cane, may be used instead of glass; and these possess the advantage of being easily cut with a sharp knife when there is any difficulty in removing the skin. Again, whether glass or fine stems are used, a little grease of any kind placed previously on the end will allow the dried skin to be slid off with less difficulty.
Preserved larvæ should preferably be mounted on small twigs or artificial imitations of the leaves of the proper food plants. A little coaguline applied to the claspers will fix them very firmly on these twigs or leaves, which are then secured in the cabinet by means of one or two small pins.
It is much to be regretted that the natural colours of many caterpillars cannot be preserved in the blown skins. Some are rendered much lighter in colour on account of the withdrawal of the contents, while others turn dark during the drying. In the smooth-skinned species the natural tints may be restored by painting or by staining with suitable aniline dyes, but these artificial imitations of the natural colours are always far less beautiful than the hues of the living larvæ.
Very few words need be said on the preservation of pupæ. Many of them do not alter much in form and colour, and therefore they require no special preparation.
If a pupa has to be killed for the purpose of adding to the value of the collection, simply plunge it into boiling water, and it is ready to be fixed in the cabinet as soon as it is quite dry.
The empty pupa cases, too, from which the perfect insects have emerged, are often worth preserving, especially if the damage done by the imago on forcing its way out is repaired with the aid of a little coaguline.
Let all larvæ and pupæ be preserved in their characteristic attitudes and positions as far as possible, so that each one tells some interesting feature of the life history of the living being it represents. Further, enrich your collection by numerous specimens of the various kinds of cocoons constructed by the larvæ, pinning each one beside its proper species; and never refuse a place to any object that relates something of the life history of the creatures you are studying.
The selection of a cabinet or other storehouse for the rapidly increasing specimens of insect forms is often a matter of no small difficulty to a youthful entomologist. Indeed, there are very many points of considerable importance to be considered before any final decision is made. Freedom from dust, the exclusion of pests, the convenience of the collector, the depth of his pocket, and the general appearance of the storehouse must be considered, and it is impossible, therefore, to describe a form that is equally suitable to all.
If it is absolutely necessary that the cabinet (or its substitute) be of a very inexpensive character, and if, at the same time, the collector has not the mechanical skill necessary for its construction, then perhaps the best thing he can do is to procure a number of shallow (about an inch and a half deep) cardboard, glass-topped boxes, such as are to be obtained at drapers' shops. For the sake of uniformity and convenience in packing, have them all of one size. Glue in small slices of cork just where the insects are to be pinned, and see that each box is supplied with either camphor or naphthaline. All the boxes may be packed in a cupboard or in a case made specially to contain them; and a label on the front of each will enable you to select any one when required without disturbing the others.
It may be mentioned here that glass is not necessary, though it is certainly convenient at times, especially when you are exhibiting your specimens to admiring non-entomological friends, who have almost always a most alarming way of bringing the tip of the first finger dangerously near as they are pointing out their favourite colours. 'Isn'tthatone a beauty?' is a common remark, andtherewith off snaps a wing of one of your choicest insects. When glass is used, however, see that the specimens are excluded from light, or the colours will soon lose their natural brilliancy.
Anyone who has a set of carpenter's tools and the ability to use them well will be able to construct for himself either a set of store boxes or a cabinet of many drawers in which to keep his natural treasures. In this case a few considerations are necessary before deciding on the form which the storehouse is to take.
A cabinet, if nicely made, forms a very sightly article of furniture; and, if space can be found for it, is the best and most convenient receptacle. One of about twelve to twenty drawers will be quite sufficient for a time; and the few following hints and suggestions may be useful.
The wood used should be well seasoned, and free from resin. The drawers should fit well, and slide without the least danger of shaking. Each one should be lined with sheet cork, about one-eighth of an inch thick, glued to the bottom, nicely levelled with sand paper, and then covered with thin, pure white paper, laid on with thin paste. It is also advisable to cover each with glass, inclosed in a light wood frame that fits so closely as to prevent the intrusion of mites.
The drawers may be arranged in a single vertical tier if the cabinet is to stand on the floor, or in two tiers if it is to be shorter for placing on the top of another piece of furniture; and glass doors, fastened by a lock and key, may be made to cover the front if such are desired as a matter of fancy, or as a precaution against the meddlesome habits of juvenile fingers.
Store boxes are sometimes chosen in preference to cabinets because they are more portable, and because they can be arranged on shelves—an important consideration when floor space is not available.
These boxes should be cork-lined and glazed like the cabinet drawers; and if they are made in two equal portions, lined with cork on both sides, and closing up like a book, they may be arranged on shelves like books, in which position they will collect but little dust.
Both store boxes and cabinets are always kept in stock by the dealers, the former ranging from a few shillings each, and the latter from fifteen shillings to a guinea per drawer. Knowing this, you can decide for yourself between the two alternatives—making and purchasing.
We have now to consider the manner in which our specimens should be arranged and labelled.
The table formingAppendix Icontains the names ofallthe British butterflies and larger moths, and shows their division intoSections,Tribes,Families, andGenera. This table is the result of most careful study on the part of leading entomologists, and shows how, in their opinion, the insects can best be arranged to show their relation to one another; and you cannot do better than adopt the same order in your collection.