DIPTERA. 499 



it is evident that they are much too large for any of the para- 

 sitical insects which attack the larvcc and egqs of the Hessian 

 and wheat flies; and they appear sometimes to have been mis- 

 taken for the latter. In an extract from a paper by Mr. Worth, 

 on the Hessian Hy, mention is made of a pale yellow worm 

 (maggot), about three sixteenths of an inch long, having been 

 found by him within the stalks of wheat near the root, where 

 its presence was detected by a swelling of the part attacked. 

 This was perhaps the larva of one of the Oscinians. A care- 

 ful examination of all the insects that inhabit our fields of 

 grain is very much wanted. 



The various insects, improperly called bot-bees, are two- 

 winged flies, and belong to the order Diptera, and the family 

 CEsTRiD^, so named from the principal genus in it. Bot-flies 

 do not seem to have any mouth or proboscis; for although 

 these parts do really exist in them, the opening of the mouth 

 is extremely small, and the proboscis is very short, and is en- 

 tirely concealed in it; so that these insects, while in the winged 

 state, do not appear to be able to take any nourishment. They 

 somewhat resemble the Syrphians in form and color, and in 

 the large size of their heads; but the eyes are proportionally 

 small, and there is a large space between them. The face is 

 swollen or puffed out before. The antenniE are very short, 

 and almost buried in two little holes, close together, on the 

 forehead. The winglets are large and entirely cover the poisers. 

 The hind body of the females ends with a conical tube, bent 

 under the body, and used for depositing the eggs, which the 

 insect lays whilst flying. The larva; or young of bot-flies live 

 in various parts of the bodies of animals. They are thick, 

 fleshy, whitish maggots, without feet, tapering towards the 

 head, which is generally armed with two hooks ; and the rings 

 of the body are surrounded with rows of smaller hooks or 

 prickles. When they are fully grown, they drop to the ground 

 and burrow in it a short distance. After this, the skin of the 

 maggot becomes a hard and brownish shell, within which the 

 insect turns to a pupa, and finally to a fly, and comes out by 

 pushing off a little piece like a lid from the small end of the 

 shefl. 



