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CHAPTER IX. 



DIPTERA (Two-winged Flies). 



From an entomological point of view, the order Diptera is very import- 

 ant, inasmuch as it is, to a large extent, an unworked field, requiring 

 a good deal of careful study, and having admittedly an unsettled 

 question of classification. Viewed by the economic entomologist, it 

 traverses a very wide field. Thus we have the troublesome flea, the 

 annoying house-fly, and the irritating summer-evening midge. There 

 are several species which feed on carrion or decayed vegetables, and 

 destroy obnoxious matter, both in the animal and vegetable kingdoms, 

 and a number of species which take an active part in disseminating 

 some of the most direful diseases. From a husbandry point of view, 

 the familiar names of warble-fly, onion-fly, carrot-fly, Hessian-fly, and 

 many others, suggest the importance of the subject. In the forest 

 they are, as a general rule, not so destructive as some of the insects 

 previously dealt with, but their small size, minute characters, and 

 interesting life -histories suggest them as interesting studies to the 

 microscopist, the general biologist, and the practical man. 



The structure of the Diptera can be best made out by taking a 

 house-fly as a typical insect. The chief character is, of course, the 

 " two - winged " structure. They are sharply marked off from all 

 other orders of insects by the reduction of the hind-wings to mere 

 knobs, " balancers," or halteres as they are termed. The whole 

 mechanism of flight is entirely dependent on the two wings, but it is 

 patent that the creatures bound through the air with greater ease, 

 more gracefulness, and apparently, as it were, more command of will, 

 than any other group of insects. 



The head is usually very convex in form, large eyes, and with so 

 slender and flexible a neck that the head all but turns round on a 

 pivot. The order shows that there is great diversity and modifica- 



