they thus serve as pitfalls, from which the insects cannot escape. If during winter little heaps of horse dung are placed on the ground, the insects creep into them for the sake of the warmth, and can thus be collected and killed. THIRD ORDER: =Neuroptera= (NET-WINGED INSECTS). Insects with biting mouth-parts and four similar membranous wings, with numerous veins arranged in a net-like manner. The metamorphosis is either incomplete (p. 89: dragon flies, may flies, book lice), or complete (p. 89: ant lions, lace flies, snake flies, scorpion flies, caddis flies). The indigenous forms, with the single exception of book lice, feed upon animal food, usually on the juices of other insects. Several of them are tolerably useful in this way. The =Dragon Flies= (_Libellulidæ_) fly about incessantly from place to place on bright warm days, and catch a large number of insects, especially butterflies and flies, among which are many that are harmful. The larvæ live in water, and feed on insects and such small deer, which, however, are of no importance to forestry or agriculture. They also devour fish-spawn, and may therefore be injurious in that way. [Illustration: FIG. 86.—The Common Lace Fly (_Chrysopa vulgaris_): _a_, eggs; _b_, the larva; _c_, cocoon; _d_, pupa contained in the same; _e_, open cocoon; _f_, adult insect; _a_, _c_, _e_, natural size; _d_, enlarged and natural size; _b_ and _f_ enlarged. ] The =Lace Flies= (_Hemerobidæ_) when at rest are covered as with a roof by their fore and hind wings, which are almost alike, clear as glass, and finely veined. Head tolerably large, eyes large, abdomen elongated and slender. The extremely rapacious larvæ (Fig. 86, _b_) feed on the juices of the bodies of other insects, which they suck up by means of a pincer-like organ situated on either side of the mouth. The two pincers are perforated, and the tubes open on each side into the gullet; the body juices of the insects attacked thus flow into the gut of the larva. This is strongly built, and always much thicker and larger than the adult insect. Metamorphosis complete. Three genera belong to the lace flies:— 1. The delicate greenish, or greenish yellow, illsmelling =Gold-eyed Lace Flies= (_Chrysopa_), the larvæ of which chiefly feed on plant lice (a few species on caterpillars, also, and other small insect larvæ). 2. The =Aphis Lions= (_Hemerobius_: _H. hirtus_, with hairy veins on the fore wings; _H. dipterus_, with hind wings almost entirely absent), the larvæ of which also feed on aphides, and make a case from their sucked-out skins.