the last of June, or early in July, the slug-like larvae
mature, and the perfect insects fly in July. Various Gall flies now lay
their eggs in the buds, leaves and stems of various kinds of oaks,
blackberries, blueberries and other plants.

[Illustration: 235. Water Flea.]

[Illustration: 236. Selandria rosae.]

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 t