A little farther on we meet with a sickly-looking plant in the midst of a number of flourishing individuals of the same species, and stop to make inquiries into the cause of this strange occurrence. Is it due to a poorness of the soil? No, this cannot be the case; for intermingled with its roots are those of its flourishing companions. We pluck a stunted and half-shrivelled leaf and examine it. At first we do not notice the cause of its peculiar condition; but, holding it up to the light, and looking _through_ it, we see a number of little galleries that have been eaten out of its internal soft substance, leaving the thin skin (_epidermis_) almost entirely intact. But nothing more is to be seen.
Another leaf is examined in exactly the same way; and here we see the little destroyer, lying motionless in its burrow till a gentle pressure applied against it from outside causes it to wriggle along its narrow pa.s.sage. This is the larva of one of the little leaf miners mentioned again on page 303.
Reaching a little marshy spot we see a number of water-loving reeds, most of them beautifully green and in a flourishing condition, but here and there in their midst is a poor stunted specimen--another result of the ravages of the larvae of one or more moths. An examination of the blades reveals nothing; but on splitting open the stalk we discover some larvae that have already devoured a quant.i.ty of the internal pith, and thus endangered the life of the plant. On inspecting other similar reeds we are at first puzzled as to how the larvae could get inside the stems without damaging the outer portion; but at last we see in each one a little discoloured hole that was eaten out by the young caterpillar just after its escape from the egg. Once within the reed, it found a plentiful supply of food, and there grew at the expense of the plant without doing any further external damage save by causing a stunted growth.
It may be that the stem eaters we have found are just about full grown.
If so we examine a number of the stems with a hope that we may find one or two that are just about to change to the chrysalis state, or even a pupa already formed. By this means we may secure one of the perfect insects without the necessity of feeding larvae at home. Such a consideration becomes a most important one when it happens that the required food plant is one that cannot be easily obtained.
Close by the reeds is another water-loving plant in the form of an old willow tree. This is always an attractive object to the entomologist, so it comes in for a share of our inspection. On its leaves we may find several species of the larvae of _Lepidoptera_, including those of some of our largest insects. But a strange feature catches our eyes as we happen to glance at the bark of the tree. Here we see a few holes of different sizes, about which are a number of little fragments of wood that remind us of "sawdust;" and, examining the ground below, we see quite a little heap of this dust, looking just as if a carpenter had been at work on the spot.
This is not the effect of a saw, however; it is a sure sign of the ravages of wood-eating larvae (p. 224), whose powerful jaws gain them admittance into the very hearts of trees, and the application of the nose to one of the larger holes leaves no doubt of the presence of the large and beautiful caterpillar of the Goat Moth (p. 224).
If we require any of these wood-eaters, either for rearing or for preservation, we must be prepared for a little rather heavy work. A strong pocket knife is not sufficient, but with a good chisel the wood can be gradually cut away, and the galleries traced, till at last we come to the larvae snugly resting in their burrows.
It often happens that the tree thus tenanted is half decayed, and consequently the work is rendered much easier. Also, while tearing away the wood, we often meet with a number of coc.o.o.ns that have been constructed by the caterpillars for their winter quarters, or as a resting place while undergoing their transformations. These are composed of the wood dust bound together by strong silk fibres, and are often in such a good state of preservation that they form useful ill.u.s.trations for the cabinet.
As further aids to larvae searching we may mention that many species--chiefly of the _Noctuae_--hide under the surface of the ground or among dense and low herbage during the day, and come out to feed only by night; that many others feed on roots, and are therefore seldom seen above the surface of the soil; also that a good number burrow into fruits, in the interior of which they spend the whole of their larval stage. The best way to secure the latter is to examine the "windfalls"
that lie scattered on orchard lands, for it is a well-known fact that the fruits that are infested with larvae generally fall earlier than others--a result that must be attributed to the damaging work of the larvae themselves.
All the larvae collected should be carefully boxed at once, a separate compartment being used for each species, and a few fragments of the food plant being introduced in each case. It is also a good plan to have each box previously lined with moss as a further addition to the comfort of the captives. Without such a precaution some of the more delicate species are liable to injury during their transmission from field to home.
Hitherto we have obtained our larvae by _searching_ only, but there are times and occasions when our boxes may be far more rapidly filled by methods that are not such a tax on our time and patience. Suppose, for instance, that we reach a bush, the mutilated leaves of which seem to show that larvae are present on its branches. We spread our white cloth or open out the white-lined umbrella just under a selected branch, and then tap that branch very smartly with our stick.
Down comes a host of living creatures! Spiders, larvae, beetles, aphides, earwigs, and what not, struggling and running about on our white fabric in all directions, and all mingled with bits of stick, leaves, and fragments of all kinds. We leave the cloth or the umbrella, as the case may be, quite still for a few seconds to allow all the living creatures to get a good foothold, and then, raising it into a vertical position, allow all the rubbish to drop off.
We can now put the cloth down again, and select as many of the larvae as we require, giving our first attention to the nimble runners and loopers that are already near the edge and just on the point of making their escape. This productive method of larva hunting is known as "beating,"
and is particularly applicable to tall herbs and the lower branches of trees and shrubs.
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 larvae 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 larvae 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 Pupae_
We have seen that ova and larvae may be obtained in greater or less abundance at all times of the year, so variable are the seasons of the different b.u.t.terflies and moths. The same remark applies equally well to pupae; 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 pupae 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 pupae.
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 coc.o.o.ns, 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 larvae, 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 pupae.
Where these exist, they are usually to be found very near the entrance, sometimes even protruding slightly from the opening, for the larvae 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 pupae and coc.o.o.ns 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 pupae 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 pupae 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 coc.o.o.ns.
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 larvae that are seeking a resting place for the winter.
Most larvae 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 pupae, and also for earthen coc.o.o.ns 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 coc.o.o.n could be easily seen; and if you have removed a gra.s.sy 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 larvae.
But the variability of your success will be quite beyond your comprehension. Sometimes you will sight a grand old oak with the most favourable antic.i.p.ations, 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 pupae 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.