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The same principle may be employed in the case of branches that are quite out of the reach of the stick, but the blows are here applied to the trunk, a mallet or some other rather heavy implement taking the place of the stick.

Another splendid method of securing larvæ where mere searching would be tedious and unproductive, lies in the use of the sweep net described on page 102. This implement comes into service in waste places that are covered with rank vegetation, in clover and hayfields, and in all spots covered with low herbs.

Walking among the vegetation, the net is swept right and left before you, and the contents examined at frequent intervals. It is advisable to work the different species of herbs separately as far as possible, otherwise there may be some difficulty in the determination of the food plants of the mixed larvæ that the net will contain. If, however, this plan is impracticable, you may save time by turning out all the 'sweepings' into one large box, leaving the sorting to be done at home in leisure hours.

Collecting Pupæ

We have seen that ova and larvæ may be obtained in greater or less abundance at all times of the year, so variable are the seasons of the different butterflies and moths. The same remark applies equally well to pupæ; but so many of the Lepidoptera spend the winter months in the chrysalis state that this period may be regarded as the harvest time of the pupa hunter.

A large number of caterpillars undergo their change to the quiescent state during the months of August and September, and, of course, remain in this state until the warm days of the following spring or summer. And as insects even in the pupal stage have a number of enemies and dangers to contend with, it is advisable to start your search for them as soon as possible after they have changed.

If you set your mind on searching for particular species, you should endeavour to ascertain the usual time at which such species pupate; make any necessary allowances for the forwardness or backwardness of the season, and then allow a week or two for the change to be completed, for insects should never be disturbed at times when their metamorphoses are in progress.

For general pupa hunting the best season is undoubtedly from the end of August to the end of October, but there is no reason why the work should not be carried on throughout the winter. If, however, you continue your work so late, you must not expect nearly as much success as time advances. You must remember that entomologists are not the only pupa hunters. Many hungry birds are always on the look-out for insects, and seem to enjoy them equally well in all their stages. Those that hybernate on or under the ground are liable to fall a prey to moles and beetles. In addition to these dangers, all pupæ are subject to the effects of extreme cold, dampness, or floods.

As regards the choice of a day, very little need be said. Any day that is sufficiently genial for yourself will do for your work, except that periods of hard frost render the ground too hard for digging – the most profitable part of the pupa hunter's task.

The apparatus required is extremely simple: A satchel or large pockets full of small metal or chip boxes, a small garden trowel, and a strong chisel.

If metal boxes are used they should be perforated; in fact, nothing is better than the ordinary larva boxes of the dealers. All the boxes, of whatever kind, should be lined with moss previous to starting work.

The trowel and chisel do not pack well with a number of small boxes, therefore it is a good plan to fix them in a couple of leather sheaths attached to your belt. In this position they are far more handy for use, and the boxes are also in less danger of being crushed or damaged, as they probably would be if in contact with hard and heavy tools.

A note book is also a valuable addition to your outfit, as it enables you to make memoranda concerning the trees and localities from which you obtain your pupæ.

The best localities for pupa hunting are clearings in woods, parks with numerous large timber trees, and meadows in which large isolated trees are scattered; and the best trees include willows, poplars, oaks, beeches, birches, elms, and hawthorns.

The best thing you can do on arriving at the selected hunting ground is to make at once for isolated trees of large size, and work each one as follows:

First examine well the crevices of the bark, for many caterpillars descend the tree to within a short distance of the ground, and then seek out a snug little crevice in which to spend the winter, often protecting themselves with silken cocoons, or constructing a neat little shelter of gnawed fragments of the wood cemented together.

If there is any loose bark, very carefully force it out with your chisel, and examine both its inner surface and the wood from which it was removed. The wood thus exposed may reveal openings of the galleries of wood-eating larvæ, in which case, unless the material is too hard to be broken up with the chisel, you may be able to trace out a few pupæ. Where these exist, they are usually to be found very near the entrance, sometimes even protruding slightly from the opening, for the larvæ generally place themselves in this position of easy escape when about to change.

Next give your attention to the moss, if any, covering the lower portion of the trunk. This affords a very favourite shelter to many species. Tear it off very carefully, beginning at the top, and watch for loose pupæ and cocoons as you do so. Then hold the clumps you have removed over a patch of bare ground or over a spread handkerchief, and pull it to pieces, in order that any pupæ it contains may fall out; also examine the fragments carefully for others that may remain attached.

This done, the surface of the ground must be examined. Remove all dead leaves, and watch for pupæ that may be sheltered beneath them. If any loose stones lie on the ground, turn them over. Search well into the angles between the roots, and if there are any holes or hollows beneath them or in the trunk itself, pull out all loose matter within, and feel gently above and around for cocoons.

After all loose matter has been removed, there still remains the soil for examination. If this is very hard and clayey, it is probably useless to carry the search any farther; also if very wet you need not expect much; but if comparatively dry and friable there are more hopes of success.

As a general rule the north and east sides of the trunk are drier than those which are exposed to the heavy rains brought by the south and south-west winds, and are consequently more favoured by larvæ that are seeking a resting place for the winter.

Most larvæ seek shelter in the angles between the roots of the trees on which they fed, but a few species seem to prefer the edges rather than the corners; and in cases where no such angles are formed at the surface, you will do well to examine the earth and turf all round the trunk; but it is generally useless to extend the search more than a few inches from the tree.

After having searched every available nook and corner as far as possible without digging, thrust the trowel obliquely into the soil a few inches from the tree, turn over the sod, and then examine the spot from which it was removed. Now give your attention to the sod itself. If loose and friable, break it up gently, keeping a sharp eye for falling pupæ, and also for earthen cocoons that are easily mistaken for little lumps of soil.

If the soil is held together by roots, it must be pulled to pieces, and the fragments shaken over a bare piece of ground where the fall of a pupa or cocoon could be easily seen; and if you have removed a grassy turf, it will be necessary to look between the bases of the blades as well as among the roots.

In this way you may search round tree after tree, wherever the soil is of such a character as to allow of the admittance and shelter of larvæ. But the variability of your success will be quite beyond your comprehension. Sometimes you will sight a grand old oak with the most favourable anticipations, and consider yourself quite certain of a good find when you discover, on a nearer approach, the liberal coating of moss that clothes its trunk and the dry sandy soil at its foot; and yet the most careful search ends in nothing but disappointment. At other times you try your luck at tree after tree without ever seeing a single pupa or even a cast-off case, and then, when just on the point of despairing, you search round another that is apparently much less promising, and, to your great surprise and delight, a dozen or two are turned out in a few minutes. Such an occurrence as this is not at all uncommon, and cannot be satisfactorily explained, but we must take things as they come and make the best of them, remembering that pupa searching is one of the best of all entomological operations wherewith to test one's perseverance and patience.

It may be mentioned, in conclusion, that the pupæ of Lepidoptera are never to be found far below the surface of the soil. Generally they exist, if buried at all, only an inch or two down, and very rarely at a greater depth than four inches.

In our next chapter we shall learn how to rear the perfect insects from the earlier stages we have been considering.

CHAPTER VIII
REARING LEPIDOPTERA

Management of Ova

In the management of insects in all stages the strictest attention must always be paid to one general rule on which the success of the work almost entirely depends; and that is – keep every specimen as far as possible under the same conditions as those in which you find it in nature.

Applying this principle to ova, we store them in airy and light places, protected from the direct rays of the sun, and avoid handling and rough treatment of any kind. It is also advisable in most cases to maintain a slight amount of dampness corresponding with that of the open air at the particular season of the year.

They do not require much space, and it is certainly desirable not to give much, otherwise the newly hatched larvæ, when their time arrives, will actively wander all round their premises in search of food, and give you no end of trouble in gathering them up.

Chip boxes are, as a rule, very good and very convenient receptacles for ova. After placing the eggs in these, cover them over with very fine muslin, held in place by elastic bands; and label each as far as you can with the name of the species contained, and other particulars worth remembering. The boxes may then be put in front of a window facing north, or in any situation within or out of doors where rain and sun cannot reach them. A greenhouse is an admirable place in which to keep them, the natural dampness of the atmosphere being apparently a considerable assistance to the tiny larvæ just as they are striving to escape from their shell.

Whatever place is selected, it is absolutely necessary that the ova be carefully watched, so that each brood may be supplied with the required food plant within a few hours of quitting the shells.

When ova are kept in a warm room, very great inconvenience and even loss is sometimes caused by the appearance of larvæ before the necessary food plant shows its buds. Yet, on the other hand, it is sometimes a great gain to the entomologist to get certain broods off early in the season, providing the food is at hand; for in this way he can not only get some of his work over during a slack season, but also, if he desires it, secure an additional brood; that is, one brood more than the usual number. Thus, supposing a certain species he is rearing is naturally double-brooded, he can, by judicious management, secure three successive broods before the food plant casts its last leaves.

This hastening of the natural events of insect life is known as forcing, and merely consists in subjecting the species concerned to a reasonable amount of artificial heat, such as that of a room in which a fire is always kept, or of a hothouse.

It is interesting at all times to note the dates on which eggs are laid or collected, and the times at which the young larvæ appear. In addition to this all changes that take place in the colours or forms of eggs should be carefully observed; for such changes will assist you in distinguishing between fertile and sterile ova, and also enable you to judge approximately as to the date of the appearance of future broods.

Rearing Larvæ

The main point in connection with the rearing of larvæ is certainly the selection and construction of the cages or their substitutes. For newly hatched and all very small caterpillars a small bottle with a wide mouth makes a very fair abode. Put a layer of sand or sifted soil in the bottom, fix in this a small twig of the food plant or lay a few leaves on the top, and then, after the larvæ have been introduced, cover the top with a piece of muslin, held in place by an elastic band.

The great drawback with this arrangement is the lack of any provision for keeping the food moist and fresh, thus rendering a change necessary at very frequent intervals; but this may be obviated by using damp sand as a foundation for the little twig of food plant. With this improvement, if you cover the top of the bottle with apiece of glass, a saucer, or any impermeable substance, you may keep the twig fresh for several days, generally until the disappearance of the last leaf calls for a fresh supply; but it is very doubtful whether the damp atmosphere resulting from this inclosure is not injurious to the larvæ. It certainly does not seem to have much influence on some, but the unhealthy conditions that result must be detrimental to the inmates. It must also be remembered that many species require a dry soil in which to burrow when about to change.

When the time comes for the change of food, great care must be taken not to injure young and small larvæ. In many cases they need never be touched, for if a fresh twig be placed beside the stale one, they will readily find their way to it; and to facilitate this, and also to afford a convenient foothold to those larvæ that accidentally fall from the twig, the layer of sand at the bottom of the bottle should be covered with moss or cocoa-nut fibre.

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 between the 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 in fig. 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, or suspend 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 rather more 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 to insect 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 sharp ovipositors into 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 Management of Pupæ

The disappointments connected with the rearing of Lepidoptera are 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; but we 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, the pupa 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.