PLATE I.7-MATURE INSECTS.
Fig. 1, Cricket; 2, Earwig; 3, Aphis; 4, Scolytus; 5, Anthrax; 6, Balaninus; 7, Cynips; 8, Ant; 9, Wasp.
PLATE II.-LARVÆ OF THE INSECTS REPRESENTED ON PLATEI.
Fig. 1, Larva of Cricket; 2, Larva of Aphis; 3, Larva of Earwig; 4, Larva of Scolytus (Beetle); 5, Larva of Anthrax (Fly); 6, Larva of Balaninus (Nut Weevil); 7, Larva of Cynips; 8, Larva of Ant; 9, Larva of Wasp.
In the Cynipidæ (Plate I., Fig. 7) the female is provided with an organ corresponding to the saw of the sawfly, but resembling a needle. With this she stings or punctures the surface of leaves, buds, stalks, or even roots of various plants. In the wound thus produced she lays one or more eggs. The effects of this proceeding, and particularly of the irritating fluid which she injects into the wound, is to produce a tumour or gall, within which the egg hatches, and on which the larva, a thick fleshy grub (Plate II., Fig. 7), feeds. In some species each gall contains a single larva; in others, several live together.
The oak supports several kinds of gallflies: one produces the well-known oak-apple, one a small swelling on the leaf resembling a currant, another a gall somewhat like an acorn, another attacks the root; the species making the bullet-like galls, which are now so common, has only existed for a few years in this country; the beautiful little spangles so common in autumn on the under side of oak leaves are the work of another species, the Cynus longipennis. One curious point about this group is, that in some of the commonest species the females alone are known, no one yet having ever succeeded in finding a male.
Another great family of the Hymenoptera is that of the ichneumons; the females lay their eggs either in or on other insects, within the bodies of which the larvæ live. These larvæ are thick, fleshy, legless grubs, and feed on the fatty tissues of their hosts, but do not attack the vital organs. When full-grown, the grubs eat their way through the skin of the insect, and turn into chrysalides. Almost every kind of insect is subject to the attacks of these little creatures, which are no doubt useful in preventing the too great multiplication of insects, and especially of caterpillars. Some species are so minute that they actually lay their eggs within those of other insects Figs. (15, 16). These parasites assume very curious forms in their larval state.
But of all the Hymenoptera, the group containing the ant, the bee, and the wasp is the most interesting. This is especially the case with the social species, though the solitary ones also are extremely remarkable. The solitary bee or wasp, for instance, forms a cell generally in the ground, places in it a sufficient amount of food, lays an egg, and closes the cell. In the case of bees, the food consists of honey; in that of wasps, the larva requires animal food, and the mother therefore places a certain number of insects in the cell, each species having its own special prey, some selecting small caterpillars, some beetles, some spiders. Cerceris bupresticida, as its name denotes, attacks beetles belonging to the genus Buprestis. Now if the Cerceris were to kill the beetle before placing it in the cell, it would decay, and the young larva, when hatched, would find only a mass of corruption. On the other hand, if the beetle were buried uninjured, in its struggles to escape it would be almost certain to destroy the egg. The wasp has, however, the instinct of stinging its prey in the centre of the nervous system, thus depriving it of motion, and let us hope of suffering, but not of life; consequently, when the young larva leaves the egg, it finds ready a sufficient store of wholesome food.
Other wasps are social, and, like the bees and ants, dwell together in communities. They live for one season, dying in autumn, except some of the females, which hibernate, awake in the spring, and form new colonies. These, however, do not, under ordinary circumstances, live through a second winter. One specimen which I kept tame through last spring and summer, lived until the end of February, but then died. The larvæ of wasps (Plate II., Fig. 9) are fat, fleshy, legless grubs. When full-grown they spin for themselves a silken covering, within which they turn into chrysalides. The oval bodies which are so numerous in ants' nests, and which are generally called ants' eggs, are really not eggs but cocoons. Ants are very fond of the honey-dew which is formed by the Aphides, and have been seen to tap the Aphides with their antennæ, as if to induce them to emit some of the sweet secretion. There is a species of Aphis which lives on the roots of grass, and some ants collect these into their nests, keeping them, in fact, just as we do cows. Moreover they collect the eggs in the autumn and tend them through the winter (when they are of no use) with the same care as their own, so as to have a supply of young Aphides in the spring. This is one of the most remarkable facts I know in the whole history of animal life. One species of red ant does no work for itself, but makes slaves of a black kind, which then do everything for their masters. The slave makers will not even put food into their own mouths, but would starve in the midst of plenty, if they had not a slave to feed them. I found, however, that I could keep them in life and health for months if I gave them a slave for an hour or two in a week to clean and feed them.
PLATE III.--MATURE INSECTS.
Fig. 1, Chloëon; 2, Meloë (after Shuckard); 3, Calepteryx; 4, Sitaris (after Shuckard); 5, Campodea (after Gervais); 6, Acilius; 7, Termes; 8, Stylops (female); 9, Thrips.
PLATE IV. YOUNG FORMS OF THE INSECTS REPRESENTED ON PLATE III.--Fig. 1, Larva of Chloëon; 2, Larva of Meloë (after Chapuis and Candèze); 3, Larva of Calepteryx (after Léon Dufour); 4, Larva of Sitaris; 5, Larva of Campodea; 6, Larva of Acilius; 7, Larva of Termes (after Blanchard); 8, Larva of Stylops; 9, Larva of Thrips.
Ants also keep a variety of beetles and other insects in their nests. That they have some reason for this seems clear, because they readily attack any unwelcome intruder; but what that reason is, we do not yet know. If these insects are to be regarded as the domestic animals of the ants, then we must admit that the ants possess more domestic animals than we do.
Some indeed of these beetles produce a secretion which is licked by the ants like the honeydew; there are others, however, which have not yet been shown to be of any use to the ants, and yet are rarely, if' ever, found, excepting in ants' nests.
M. Lespès, who regards these insects as true domestic animals, has recorded8 some interesting observations on the relations between one of them (Claviger Duvalii) and the ants (Lasius niger) with which it lives. This species of Claviger is never met with except in ants' nests, though on the other hand there are many communities of Lasius which possess none of these beetles; and M. Lespès found that when he placed Clavigers in a nest of ants which had none of their own, the beetles were immediately killed and eaten, the ants themselves being on the other hand kindly received by other communities of the same species. He concludes from these observations that some communities of ants are more advanced in civilization than others; the suggestion is no doubt ingenious, and the fact curiously resembles the experience of navigators who have endeavoured to introduce domestic animals among barbarous tribes; but M. Lepès has not yet, so far as I am aware, published the details of his observations, without which it is impossible to form a decided opinion. I have sometimes wondered whether the ants have any feeling of reverence for these beetles; but the whole subject is as yet very obscure, and would well repay careful study.
The order Strepsiptera are a small, but very remarkable group of insects, parasitic on bees and wasps. The larva (Pl. IV., Fig. 8) is minute, six-legged, and very active; it passes through its transformations within the body of the bee or wasp. The male and female are very dissimilar. The males are minute, very active, short-lived, and excitable, with one pair of large membranous wings. The females (Pl. III., Fig. 8), on the contrary, are almost motionless, and shaped very much like a bottle; they never quit the body of the bee, but only thrust out the top of the bottle between the abdominal rings of the bee.
In the order Coleoptera, the larvæ differ very much in form. The majority are elongated, active, hexapod, and more or less depressed; but those of the Weevils (Pl. II., Fig. 6), of Scolytus (Pl. II., Fig. 4), &c., which are vegetable feeders, and live surrounded by their food,-as, for instance, in grain, nuts, &c.,-are apod, white, fleshy grubs, not unlike those of bees and ants. The larvæ of the Longicorns, which live inside trees, are long, soft, and fleshy, with six short legs. The Geodephaga, corresponding with the Linnæan genera Cicindela and Carabus, have six-legged, slender, carnivorous larvæ; those of Cicindela, which waylay their prey, being less active than the hunting larvæ of the Carabidæ. The Hydradephaga, or water-beetles (Dyticidæ and Gyrinidæ), have long and narrow larvæ (Pl. IV., Fig. 6), with strong sickle-shaped jaws, short antennæ, four...
