Lepidoptera Facts Collecting Butterfly And Moth Pupa
We have seen that ova and larva 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 pupa; 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 pupa 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 pupa.
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 larva, 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 pupa. Where these exist, they are usually to be found very near the entrance, sometimes even protruding slightly from the opening, for the larva 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 pupa 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 pupa 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 pupa 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 larva that are seeking a resting place for the winter.
Most larva 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 pupa, 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 larva. 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 pupa 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.