Perhaps another word of explanation is necessary here. Why not allow the poor creatures to reach the sugar that attracted them to the spot? The reason is this. They sometimes gorge themselves to such an extent that their bodies, dilated to the fullest capacity with syrup, are a bit troublesome when the insects are placed in the cabinet. It is therefore advisable to see that the zinc is so far above the sugar that the moths are unable to reach the latter by thrusting their extended proboscides through the perforations. A few dead leaves scattered on the zinc is also a useful addition, since it affords shelter to such of the insects as prefer it.
This is a very useful trap to keep in one"s garden throughout the season. It may not attract large numbers, but it has the advantage that it requires no watching. It is simply necessary to set it at dusk, and remove the captives in the morning or at your leisure.
CHAPTER VII
_COLLECTING OVA, LARVae, AND PUPae_
We have already observed that insects should, as a rule, be set as soon as possible after their capture; and it would therefore seem that this is the proper place for instructions in this part of the work. But it so happens that b.u.t.terflies and moths are to be obtained by means other than those already described, and we shall therefore consider these previous to the study of the various processes connected with the setting and preserving of our specimens.
Were we to confine our attention to the capture of the perfect forms only, our knowledge of the _Lepidoptera_ would be scanty indeed, for we should then be ignorant of the earlier stages of the creatures" lives, and have no opportunity of witnessing the wonderful transformations through which they have to pa.s.s.
Such an imperfect acquaintance with b.u.t.terflies and moths will, I hope, not satisfy the readers of these pages; so it is intended, in the next two chapters, to give a little a.s.sistance to those who would like to know how to set to work at the collection of their eggs and larvae, how to search for the pupae, and how to rear the insects from the stage at which they are acquired till they finally emerge in the perfect form.
These portions of an entomologist"s work certainly take up a great deal of his time, and also require much patience and perseverance; but the advantages derived cannot be over-estimated, for in addition to the knowledge gained of the early stages of insect life, this kind of work will enable him to place in his cabinet a number of gems he would otherwise have not and probably know not. Occasionally a prize may be obtained in the form of a cl.u.s.ter of eggs (_ova_) of a rare species, in many instances the larvae are to be obtained with comparative ease, while the perfect insects of the same species are not often seen or not easily captured, and many a rare pupa has been dug out of its hiding place during a season when the entomologist had but little other work to occupy his time.
These and other similar subjects we shall now consider in turn.
_Collecting Ova_
The collection of ova may be carried on more or less throughout the year. A number of moths are out in February, and even in January if the weather is mild. These soon lay their eggs, which are hatched about the time that the buds of the food plant are breaking. From this time till late in the summer the ova of various species are being deposited, the average period from laying to hatching being from two to three weeks.
Then, during the autumn, when the leaves of food plants are turning brown and crisp, ova are still being laid, but these remain unchanged till the new buds of the following spring are bursting.
Of course if you intend searching for the ova of particular species you must previously ascertain the favourite haunts of those species, become acquainted with their food plants, and also with the season or seasons during which the eggs are laid. But the few following hints will suffice as general instructions for the search.
In nearly all cases we must expect to find ova on the food plants of the respective species, but at times, especially with certain moths, we may come across them in the most unlikely spots. Thus, it sometimes happens that a moth settles on a street lamp, and lays her eggs on the framework round the gla.s.s, or even on the gla.s.s itself. The same thing may take place on the sash or gla.s.s of a brightly lighted window.
Such occurrences, however, we must regard as accidental and comparatively rare, and therefore we confine our searchings for ova to the food plants of the species we require.
As a rule the under sides of the leaves will yield the most, but we have already noticed (page 18) that some moths leave their eggs exposed on the upper surface. Again, some larvae feed on flowers and seeds and fruit, and the eggs of such are deposited on these parts. Those insects which feed on the leaves of shrubs and trees often lay their eggs on trunks, branches and twigs. Sometimes these are laid singly, sometimes in dense cl.u.s.ters; and it is not unusual to find them arranged in rings or spirals with great regularity. When examining the trunks of trees for ova it is necessary to look well into the crevices of the bark, for some insects take particular care to lay them in deep sheltered c.h.i.n.ks; but others take no such precautions, and deposit them on exposed ridges or plain surfaces where they are easily discovered.
One difficulty of the ova collector lies in the fact that many insects lay on the upper branches of large trees. Of course a search for these is out of the question; but in places where the trees have been cut down a few years previously, and where a consequent undergrowth has developed, there are considerable chances of success with these species.
Young saplings of trees often yield well, especially in places where tall trees of the same species are absent. It may be mentioned, too, that some moths (page 294) actually lay their eggs beneath the surface of water, depositing them on the under surfaces of floating pond weeds; and others (page 298) even enter the nests of wasps and bees for the same purpose. It is clear, then, from these few remarks, that the work of an ambitious collector of insects" eggs is by no means a monotonous task; for his employment takes him into the meadows and woods, leads him to the banks of ponds, and even compels him to tear down banks and hedges for the nests of _Hymenoptera_ at the risk of a sting or two.
One of the most productive sources of eggs is undoubtedly the possession of captured females. When you are out netting b.u.t.terflies you often see a female that is evidently engaged in her matronly duties. Instead of seeking food from the various flowers in her path, she pays attention only to the foliage, looking out a suitable leaf on which to deposit her eggs. Should you meet with an insect thus engaged which you would like to rear at home, or of which you would like to know the egg, secure it in a perforated pill box with a leaf of the proper plant; and it will often supply you with abundance of eggs for your purpose, in many cases depositing them in the box before you arrive home. The eggs of numerous species of moths are also to be easily obtained from captured females.
Some insects do not seem inclined to deposit their eggs in captivity as freely as when at large, and in order to induce them to do so we must, as far as possible, put them in their natural conditions. Let them have plenty of room, and supply them with fresh twigs of their food plants, kept green by standing them in vessels of water. It is also advisable, supposing you are not well acquainted with the dispositions of the species you have, to keep a portion of the box well shaded from direct sunlight, and allow another part to be as bright as possible; for some species will not lay in a bright light, while others will not do so without it.
Again, while some deposit their eggs within a few hours of quitting the pupa case, others do not lay for several days. With regard to the latter, it is frequently necessary to feed them while in captivity, by placing in the box a piece of rag or sponge that has been dipped in honey or syrup.
Each batch of ova should be carefully examined with a view to knowing them by sight on a future occasion. A sketch should be made in your note book, showing every detail that you can make out with the aid of a good lens. Then observations concerning the season, colour of the eggs, the situation in which deposited, arrangement, and any other useful particulars, should be entered.
In the next chapter some hints will be given concerning the management of ova and the rearing of the larvae from the time of hatching.
_Collecting Larvae_
This occupation is generally far more productive to the entomologist than searching for ova. The latter are very small, usually well concealed, and to be detected only by a careful scrutinising use of the eyes; but the superior size of the larvae, the frequent bright colouring, and the fact that they are easily beaten from their hold, render the searchings of their hunters comparatively easy and fruitful.
Before setting out on a larva-hunting expedition, there are a few requisites to prepare. These include not only the implements for your work in the field, but also the cages in which you intend to rear your little captives. The latter are described a little later on under the head "Rearing Lepidoptera," and the former we will now briefly summarise.
The outfit must consist of a quant.i.ty of suitable boxes, a stout hooked stick, a strong net, and a white material to place under the herbage while you are "beating."
"Larva boxes" are usually made of zinc, and have little sliding doors in the lids, so that the lids need not be removed while out of doors after the fragment of the required food plant has been inserted. Such boxes are not by any means essential. Small tin boxes will answer all purposes nearly as well, providing a number of small holes be made in them for the admission of air. Chip boxes are also fairly satisfactory, but these also should be perforated. The best way to do this is to push a red-hot iron wire through the chip, making about half a dozen small holes in each box. This method will give you clean holes of a uniform size without otherwise injuring the boxes.
Metal boxes possess the advantage that they keep the food plants moist for a long time, while chip boxes allow them to dry rather rapidly. Yet there are some larvae that do far better in the latter, since such a quant.i.ty of moisture exudes through their skins that they soon become uncomfortably wet if their apartment is not well ventilated. Under these circ.u.mstances perhaps it is better to take a supply of both, so that changes may be made as found necessary.
One grave objection to chip boxes, however, is the weakness of the material. They are easily crushed by pressure, and a bottom or a top disc of wood often falls out; but this is easily overcome by gluing narrow strips of calico round the top and bottom edges. Chip boxes should always be treated in this way, and they will then last five or six times as long.
Your supply of boxes should always include one large one of metal in which to bring home a supply of food for the larvae. If you have a botanist"s vasculum, by all means take it, for nothing can serve this purpose better. If not, any rather large square tin box will do, and this may be carried in your satchel, or a couple of hooks may be soldered to it so that a leather strap can be fixed for slinging it over your shoulder.
The net required is that commonly known as the "sweep net." It must be very strong, for it has to submit to rather rough usage. The frame must be made of thick wire; and the bag, which need not be more than a foot deep, should be of strong calico or holland.
Now with regard to the white material previously mentioned. This may be a square of calico, hemmed round the edges. Nothing is more convenient than this, as it occupies but little room in the pocket when not in use, if neatly folded. The material need not be thick, but the larger it is the better. Many prefer a white umbrella or an ordinary umbrella with a white lining, but as this is only a matter of taste and convenience you must decide for yourself as to which you will use.
If your field of operations is only a little way from your head quarters, and quant.i.ty of luggage therefore not a serious consideration, you may provide yourself with a heavy mallet, loaded if necessary with a pound or two of lead. This will prove very useful in shaking larvae from trees and large branches. Lastly, take a pencil and a note book or writing paper for your observations in the field.
Now for the choice of the season. Larvae are to be found all the year round. Early in the spring, as soon as the buds are bursting, some break out of the eggs recently laid by the moths that appear in February and March. Later on, during April and May, a host of both b.u.t.terflies and moths are busy arranging for their broods. Then, throughout the whole of the summer, thousands of caterpillars of all sorts and sizes are to be met with everywhere. And finally, during the bleak winter months, you may amuse yourself by digging the hybernators out of their hiding places where they rest themselves till the spring sun again calls them out to refresh them with the young and tender leaves of a new year. Thus, unless you are merely intending to search out certain species you happen to require, there is not much difficulty in settling on the season.
The day selected should be dry, for your work lies among the herbage of banks, meadows, and woods, and nothing is more unpleasant than wading through a wet and dense vegetation, or beating down on yourself a shower of large drops from the branches of trees and shrubs.
Having reached the hunting ground, the first thing to do is to look out for _signs_ of the presence of larvae rather than for the larvae themselves. Healthy vegetation with sound leaves must be pa.s.sed by as untenanted; but the presence of partly eaten foliage immediately arouses suspicion.
A little experience will soon enable you to distinguish between the ravages of larvae and of slugs, snails, wasps, &c. Some of the smaller larvae certainly eat out clean holes like those cut by _Hymenopterous_ insects, but as a rule they bite away at the edges, leaving the midrib and the larger veins standing out almost naked.
By looking well into the edges of the eaten leaves, it is easy to see whether the marauders have been recently at work. If they are dried up and discoloured, it is not of much use to search; but if still green and moist, you may feel almost sure that the hungry larvae are not far off.
In this case you will carefully turn over the leaves to examine the under sides, and also the leaf stalks and branches or stems; but you must be prepared for all kinds of protective mimicry. Little green caterpillars will be seen lying on the midrib or veins, so straight and so still that they are scarcely perceptible. Others are snugly tucked in a depression of a leaf with the same result. Then we must also be prepared for the artful little tricks of the larvae of _Geometrae_ (p.
268), by which they imitate stalks and twigs so closely that a sharp eye is necessary to discriminate between the two.
While thus searching we may meet with the cast skin of a caterpillar.
This gives us fresh hopes, and so we continue our careful examination.
At last, on grasping a leaf in order to turn it over for inspection, we feel something hairy or something soft and smooth. But lo! it is gone.
It is one of those numerous caterpillars that feign death and drop to the ground on the slightest sign of danger. We search below for it, but the density of the vegetation renders this hopeless, and we are just about to start off in search of a more productive locality when we espy a quant.i.ty of the excrement of larvae lying on a little bare patch of ground close by. This gives us a new idea. Here is another indication of the presence of the creatures we require, one that we can put into practice; and by-and-by we learn that in many cases this is really the surest sign of their whereabouts.
We look at these little pellets of excrement, and gain at once some idea of the _size_ of the larvae that produce them. Then we observe whether they are fresh and moist, or dry and stale. If the latter, it is not of much use to examine the leaves above; but if otherwise, there is little doubt of our meeting with larvae, as the present position they occupy is so truly marked. The leaves just over them are carefully examined, either by turning them over as before described, or, if the height of the foliage admits of it, by placing our heads below and looking upward.
If we find that the larvae are some of those that endeavour to escape by feigning death and allowing themselves to drop at the slightest disturbance, the net is always kept beneath the leaves we are touching in order to intercept them in their downward journey.
Continuing the search, we meet with leaves that are rolled up and bound with silk threads, and others that are drawn together and similarly bound. These are carefully uncurled and pulled asunder with the result that active little larvae are exposed to view, or, it may be, pupae are discovered. In some cases flowers are drawn together in just the same way, and an examination reveals one or more of the species that prefer petals and other parts of flowers to the green leaves.
Silken threads always arouse our suspicions. These may be seen lying on the surfaces of leaves, and pa.s.sing from one leaf to another, or they may be hanging perpendicularly from the branches of trees above. In the latter case a larva may be frequently seen on the lower extremity of the fibre, swinging gently in the breeze, and, should we require it, we have only to place the open box below for its reception.
Hawthorn and other trees are sometimes seen almost devoid of leaves, nearly every bit of green having been greedily devoured by a host of small larvae. In such cases we often meet with dense cl.u.s.ters of silk fibres that may easily be mistaken for spiders" nests. But when we look more closely into the structure we observe that we have discovered instead nests of gregarious larvae, such a large number being in each little community that the deplorable appearance of the tree is at once explained.