Dipterous Gall flies are now laying their eggs in cereals. The Hessian fly (Cecidomyia destructor) has two broods, the fly appearing both in spring and autumn. The fly lays twenty or thirty eggs in a crease in the leaf of the young plant. In about four days, in warm weather, they hatch, and the pale-red larvae crawl down the leaf, working their way in between it and the main stalk, passing downward till they come to a joint, just above which they remain, a little below the surface of the ground, with the head towards the root of the plant. Here they imbibe the sap by suction alone, and, by the simple pressure of their bodies become imbedded in the side of the stem. Two or three larvae thus imbedded serve to weaken the plant and cause it to wither and die. The second brood of larvae remains through the winter in the flax-seed, or puparium. By turning the stubble with the plough in the autumn and early spring, its imago may be destroyed, and thus its ravages may be checked. (Figure 237 represents the female, which is about one-third as large as a mosquito: _a_, the larva; _b_, the pupa; and _c_ represents the joint near the ground where the maggots live.) The same may be said of the Wheat midge (Cecidomyia tritici), which attacks the wheat in the ear, and which transforms an inch deep beneath the surface. [Illustration: 237. Hessian Fly.] [Illustration: 238. Turnip Butterfly.] Among the butterflies which appear this month are the Turnip butterfly (Pontia oleracea, Fig. 238,) which lays its eggs the last of the month. The eggs hatch in a week or ten days, and in about two weeks the larva changes to a chrysalis. Thanaos junevalis and T. Brizo fly late in May. The caterpillars live on the pea and other papilionaceous plants. Thecla Auburniana, T. Niphon, and other species fly in dry, sunny fields, some in April. Argynnis Myrina flies from the last of May through June, and a second brood appears in August and September. Vanessa J-album and V. interrogationis appear in May, and again in August and September. The caterpillars of the latter species live on the elm, lime and hop-vine. Grapta comma also feeds on the hop. Alypia 8-maculata (Fig. 49) flies at this time, and in August its larva feeds on the grape. Sphinx gordius, S. 5-maculata (Fig. 239) and other Sphinges and Sesia (the Clear-winged moth), appear the last of May. Arctia Arge, A. virgo, A. phalerata and other species fly from the last of May through the summer. Hyphantria textor, the Fall-weaver, is found in May or June. The moth of the Salt-marsh caterpillar appears at this time, and various Cut worms (Agrotis, Fig. 240) abound, hiding in the daytime under stones and sticks, etc., while various Tineids and Tortrices, or Leaf-rolling caterpillars, begin to devour tender leaves and buds and opening blossoms of flowers and fruit trees. [Illustration: 239. Sphinx 5-maculata, Larva and Pupa.] [Illustration: 240. Cut Worm and Moth.]