In the Vapourer Moth ([Fig. 228]), whose “looping” flight may often be observed even in the streets of towns during the day, the two sexes are remarkably different from each other. The male (C) alone can fly; the female (D) is wingless, and is confined for the whole of her short adult life to the place where she emerged from the cocoon. Here she lays her eggs and then dies. Neither she nor her mate is capable of feeding.
Fig. 228.—Stages of Vapourer Moth. A, Larva (male); B, male pupa; C, male moth; D, female moth. (From a photograph by Mr. A. Flatters.) (× ⅚.)
It would be difficult to find a more striking example of the fact that the one duty of the adult moth is reproduction. The female vapourer is even debarred from the privilege of choosing favourable places for her eggs; but a compensation for this disadvantage lies in the agility of the larvae (A), which are able to migrate without difficulty to another plant whenever food becomes scarce. As Prof. Miall remarks:[33] “Whatever the larva can do for itself, the female can safely leave undone; but what the larva cannot do, by reason of sluggishness or restricted diet, the parent must provide for. Hence activity and intelligence in the one lead to degeneration in the other.... Wings are to insects what spores are to ferns, plumed seeds to dandelions, and hooked seeds to burrs—a ready means of dispersal.”
Other insects.—Space does not permit of more than a reference to other insects, and the work of this chapter is to be regarded as the merest introduction to the study of this fascinating class of animals. The chief remaining orders are the Neuroptera, including May flies, dragon flies, and caddis flies; the Hemiptera, among which are included the various “bugs,” water boatmen, plant lice, etc.; the Diptera (two-winged flies), such as the house-fly, gnat, harlequin fly, daddy-long-legs, etc.; and the Hymenoptera, including bees, wasps, ants, gall flies ([p. 146]), and ichneumons. Many of these insects have aquatic larvae which may be found in ponds; and their life-histories should be studied in aquaria and careful notes made of the transformations.[34]
EXERCISES ON CHAPTER XIX.
1. Examine the following animals, and find out (a) which are arthropods, (b) which are insects: tortoise, spider, grasshopper, lobster, earwig, centipede. Give reasons for your conclusions.
2. Keep a grasshopper under a tumbler with a small sod of grass. Observe its habits, and find out how it “chirps.” Compare its structure with that of the cockroach.
3. Compare a cockchafer with a water-beetle. In what order of insects would you place the cockchafer, and why?