LEAF-EATING INSECTS OF SHADE-TREES.
Tussock Moth: 1, caterpillar (black and yellow, head red); 2, male moth (mottled gray); 3, wingless female laying eggs on her recently vacated cocoon; 4, cocoons; 5, cast skins of young caterpillars; 6, work of youth caterpillars under the surface of a leaf; 7, male pupa; 8, branch girdled by caterpillar; 9, broken end of girdled twig. Forest Tent-Caterpillar: 10, female moth (buff); 11, male moth (rust-red); 12, egg-belt; 13, fully grown caterpillar, or "maple-worm" (dull blue, red-streaked); 14, cocoon in leaf; 15, pupa; 16, cast skins.
Ichneumon-Flies
This is the last group of Hymenoptera that we can mention. These insects lay their eggs in the bodies of caterpillars or chrysalids, and sometimes in those of spiders, boring holes to receive them by means of their little sting-like ovipositors. Before long the eggs hatch, and the little grubs at once begin to feed upon the flesh of their victims. For some little time, strange to say, the unfortunate creature seems to suffer no pain, or even discomfort, but goes on feeding and growing just as before, although hundreds of hungry little grubs may be nibbling away inside it. Sooner or later, however, it dies; and then the little grubs spin cocoons and turn to chrysalids, out of which other little flies appear in due course, just like the parents.
Millions of caterpillars are destroyed by these little flies every year. Out of every hundred of those which do so much damage to our cabbages and cauliflowers, for example, at least ninety are sure to be "stung." Indeed, if it were not for ichneumon-flies we should find it quite impossible to grow any crops at all, for they would all be eaten up by caterpillars.
Lepidoptera
Next we come to the butterflies and moths, which are called Lepidoptera, or scale-winged insects, because their wings are covered with thousands upon thousands of tiny scales. If you catch a butterfly, a kind of mealy dust comes off upon your fingers, and if you look at a little of this dust through a microscope, you find that it consists simply of little scales, of all sorts of shapes. Some are like battledores, and some like masons' trowels, and they are nearly always most beautifully sculptured and chiseled. These scales lie upon the wing in rows, which overlap one another like the slates on the roof of a house. And sometimes there are several millions on the wings of a single insect.
Butterflies