No. 12. 



The Hessian Fly. 



365 



ever been found in Germany; and it is cer- 

 tain that, if the wheat were leaped in the 

 ordinary manner, nearly all the available 

 insects would be left in the stubble ; and, 

 further, tlie straw alleged to have been 

 brought by the Hessians, must have been 

 that which ripened in the summer of 1775, 

 and from which most of the insects which 

 it contained would have escaped before Au- 

 gust, 1776. On a question of such uncer- 

 tainty, no one need quarrel with another's 

 opinion. 



The first scientific description of the Hes- 

 sian fly was published in the Journal of the 

 Academy of Natural Sciences of Philadel- 

 phia, for July, 1817, No. 3. i. 45, by the late 

 distinguished entomologist, Thomas Say. 

 He there gives it the systematic name of 

 the cecidornyia destructor ; and to his de- 

 scription adds a few remarks relative to its 

 habits, and furnishes, also, an account of 

 another insect, by which tlie fly is often de- 

 stroyed. Without going into a minute and 

 tedious technical description, the following 

 account is otfered as probably suflicient to 

 enable an observer to identify the insect in 

 its various transformations: the Hessian fly 

 is a two-winged insect, with head, eyes, and 

 thorax black; the head is small and de- 

 pressed; the palpi, or mouth feelers, are 

 three or four joinj^ d — the basal one being 

 the smallest ; the antenna are about half as 

 long as the body, and consist each of 14 to 

 17 oval joints, besides the basal joint, which 

 appears double ; the wings are large, hairy, 

 rounded at the tip, and have each two or 

 three longitudinal nervures; the abdomen 

 is of a tawny red, and furnished, irregularly, 

 with many black hairs; consists of seven 

 rings or segments, besides the ovipositor, 

 which is of two sides, and of a rose-red co- 

 lour; the ovipositor, when extended to the 

 utmost, is about one-third as long as the ab- 

 domen ; length of the body, from the front 

 of the head to tlie end of the abdomen, about 

 one-eighth of an inch; the legs are long and 

 slender, pale red, and covered sparsely with 

 dark hair. The male is equal in size to the 

 female, but generally less black, with an- 

 tenna; somewhat longer, and about three- 

 fourths the length of the body. The joints 

 of the antennte are globular, and slightly 

 separated from each other. Several other 

 species of the genus cecidomyiu, or one 

 closely allied to it, are common in this re- 

 gion. But the Hessian fly is the largest 

 and darkest of our species with which I am 

 acquainted. 



The eggs are laid in the long creases or 

 furrows of the upper surface of tlie leaves, — 

 i. e., the blade or strap-shaped part — of the 

 young wheat plant. 



While depositing her eggs, the insect 

 stands with her head towards the point or 

 extremity of the leaf, and at various dis- 

 tances between the point and where the 

 leaf joins and surrounds the stalk. The 

 number found on a single leaf varies from a 

 single egg up to thirty, or even more. The ' 

 egg is about a fiftieth of an inch long, cyl- 

 indrical, rounded at the ends, glossy and 

 translucent, of a pale red colour, becoming 

 in a few hours, irregularly spotted with 

 deeper red. Between its exclusion and its 

 hatching, these red spots are continually 

 changing in number, size, and position; and 

 sometimes nearly all disappear. A little 

 while before hatching, two lateral rows of 

 opaque white spots, about ten in number, 

 can be seen in each egg. In four days, 

 more or less, according to the weather, the 

 egg is hatched; the little wrinkled maggot, 

 or larva, creeps out of the delicate membra- 

 nous egg-skin, crawls down the leaf, enters 

 the sheath, and proceeds along the stalk, 

 usually as far as the next joint below. 

 Here it fastens, lengthwise and head down- 

 wards, to the tender stalk, and lives upon 

 the sap. It does not gnaw the stalk, nor 

 does it enter the central cavity thereof; but, 

 as the larva increases in size, it gradually 

 becomes imbedded in the substance of the 

 stalk. After taking its station the larva 

 moves no more, gradually loses its reddish 

 colour and wrinklofl appearance, becomes 

 plump and torpid, is at first semi-translu- 

 cent, and then more and more clouded with 

 internal white spots ; and, when near matu- 

 rity, the middle of the intestinal parts is of 

 a greenish colour. In five or six weeks — 

 varying with the season — the larva begins 

 to turn brown, and soon becomes of a bright 

 chesnut colour. In that state, the insect 

 bears some resemblance to a flax-seed ; and 

 many observers speak of this as the flax- 

 seed state. The larva has now become a 

 chrysalis, or pupa, and takes no more food. 

 The pupa within gradually cleaves off" from 

 the outer skin, and, in the course of two or 

 three weeks, is entirely detached from it, so 

 that the skin of the larva — now brown and 

 hardened, and of a sort of leathery texture — 

 has become a case or shell for the pupa in- 

 side. The pripa shell is, of course, in size 

 and form, like the larva: it is oval, bulging 

 out beneath, and of the same curve above 

 as the outside of the stalk; divided by cross 

 lines into twelve segments, and is about an 

 eighth of an inch long. Within this shell 

 the pupa gradually advances towards the 

 winged state; it contracts in length, but not 

 in breadth; and its skin appears covered 

 with minute elevations. Just before evolu- 

 tion, we find the pupa invested in a delicate 



