DIPTERA. 401 



DIPTERA. 



Gnats and Flies. — Maggots. — Remarks upon and Descriptions of some of 

 the Diptera. — Radish-Fly. — Two-winged Gall-Flies, and Fruit-Flies. 

 — Hessian Fly Wheat-Fly. — Conclusion. 



Under the name of Diptera, signifying two-winged, are in- 

 cluded all the insects that have only two wings, and are provided 

 with two little, knobbed threads in the place of hind-wings, and a 

 mouth formed for sucking or lapping. 



Various kinds of gnats and of flies are therefore the insects 

 belonging to this order. The proboscis or sucker, wherewith 

 they take their food, is placed under the head, and sometimes can 

 be drawn up and concealed, partly or wholly, within the cavity of 

 the mouth. It consists of a long gutter, usually ending with two 

 fleshy lips, and enclosing, in the channel on its upper side, sever- 

 al fine bristles, from two to six in number, which are sometimes 

 as sharp as needles, and are then capable of inflicting severe 

 punctures. These piercing bristles really take the place of the 

 jaws of biting insects, and hence the wounds made therewith, by 

 gnats and mosquitos, are very properly called bites. The saliva 

 of these insects flowing into the wounds, renders them more 

 painful, and is the cause of the inflammation and itching that follow. 

 The grooved sheath of the proboscis is usually very large and 

 fleshy in the flies that only lap or sip their food. Two small, 

 jointed feelers are commonly found attached to the base of the pro- 

 boscis. Gnats and flies have softer bodies than most other winged 

 insects. The head is large, and fastened to the thorax by a very 

 slender neck. The eyes, especially in the males, are large, and 

 occupy the whole of the sides of the head. The antennae, in 

 gnats and mosquitos, are rather long, slender, and many-jointed ; 

 in flies, they are short, consisting of only two or three thick 

 joints, the last of which often bears a little bristle or delicate 

 feather. The wings are filmy, like those of Hymenopterous in- 

 sects, but usually have a greater number of veins in them. Just 

 behind the wing-joints there are two little, convex scales, which 



51 



