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DESCRIPTION OF THE HESSIAN FLY. 
This insect belongs to the Diptera or two-winged insects, of which 
the common house fly is the best-known type. It belongs to the 
family Cecidomyidce, a large group of minute flies, resembling the 
crane flies or daddy-long-legs ( Tipulidce ), but of dimunitive form. 
They are nearly all gall-flies, the females laying their eggs by means 
of the soft extensible end of the body which slides back and forth 
like the joints of a telescope. The irritation caused by the eggs 
results in the swelling of the stems of plants, or the formation of 
tumors or galls on the leaves and buds. The Hessian-fly, as we 
shall see farther on, does not produce true galls in this way, but 
the presence of the insect in the flaxseed state, between the leaf 
and the stalk, causes the stem to swell, and the leaves to wither 
and die. The scientific name is Cecidomyia destructor of Say. 
The female (Plate I,/; II, -4.)—The body is rather slender, uni¬ 
formly dark brown, the head is round, but somewhat flattened, the 
eyes are black, the wings uniformly dull smoky brown, while the 
legs are paler brown than the rest of the upper side of the body. 
The body, wings and legs are provided with fine hair-like scales 
(Plate II, A, c), those on the wings being in many cases quite broad 
and ribbed, somewhat like the scales on the wings of a butterfly or 
moth. The pale brown antennae are about half as long as the body, 
the joints are very distinct, like a string of beads, each one being 
oval-cylindrical. There are seventeen joints, the two basal ones being 
large, nearly globular, flattened lengthwise, and nearly half as long 
as thick, and each of nearly equal size; joints 3-5 are longer than 
the remaining ones, and are slightly contracted in the middle; the 
remaining 6-17 gradually decrease in length, each joint being pro¬ 
vided with about ten hairs, arranged in a rude whorl; the terminal 
joint (Plate II, A, a) is long and conical. The legs are of the same 
color as the under side of the body, being a little paler than the 
back. The abdomen is rather full, with nine well-marked rings or 
segments, the paler small ovipositor forming the tenth. The latter 
is one-half as thick as the ninth segment, and about two-thirds or 
quite as long; is slightly sinuous and a little smaller at the end 
than at the base. The wings are dusky, with a fine fringe around 
the edge, and there are three veins. The subcostal vein ends near 
the base of the submedian vein and runs nearly parallel to the sub¬ 
costal vein, while a branch (its base disconnected with the main 
vein) extends along the middle of the wing; the submedian vein is 
w r ell developed, at the base throwing off the median vein at a little 
distance from the base of the wing, and losing itself before turning 
down to the edge of the wing. The length of the fly is 2g- milli¬ 
meters, or about one line, i. e ., one-tentli of an inch. 
The male .—The male is rather smaller than the female, being dis¬ 
tinguished by the long slender abdomen, and the longer and more 
hairy antennae. The joints of the latter (Fig. A, a", a'") are twen¬ 
ty in number, oval, the terminal one conical, and all provided with 
a few hairs, much longer than in the female, and arranged in a 
decidedly verticillate manner. “The abdomen in the living speci¬ 
men is black or brownish black, with bands at the sutures both 
