FIELD BOOK OF PONDS AND STREAMS 



Flies — Diptera 



Flies have but one pair of wings, front ones, the second pair 

 being represented only by little clublike projections called 

 halteres. Flies include the familiar houseflies and mosqui- 

 toes. Dragonflies, mayflies, stoneflies, caddis flies and the 

 like have four wings and are not flies. Flies undergo a com- 

 plete change of form in larval, pupal, and adult stages. The 

 Diptera form a vast group both in numbers of species and 

 individuals, more than twelve thousand species having been 

 found in North America. 



Among them are many families whose larvas are aquatic 

 and a few whose pupae are also aquatic. These include the 

 gnats, punkies, midges, mosquitoes, horseflies, and craneflies. 

 The worm-like larvse are of diverse forms and sizes ; thousands 

 of midge larvae are no longer than a quarter of an inch while 

 some of the cranefiy larvae are more than two inches long. 

 The pupae may live in the water as do the midges and mosqui- 

 toes or in damp places near the water like many of the crane- 

 flies. Although the adults fly about in the region near water 

 they are by no means confined to it. All adult flies suck their 

 food through their tube-like lower lip or labium. 



The habits of the aquatic flies are so various that they are 

 best considered by separate groups. 



Identification. — Key to families of Diptera larvas from man- 

 uscript key by Dr. C. P. Alexander (slightly modified). 



Key to Diptera 



Laiva& 



1. Caudal end of body prolonged into a long extensile 



breathing-tube; rat-tail maggot and similar types. 2 

 Caudal end of body not prod,uced. 3 



2. Head forming a complete non-retractile capsule. 



Phantom craneflies, PtychopteridcB, p. 287 

 Head reduced, capable of retraction within the body; 

 true rat-tail maggots. 



Syrphus-flies, Syrphidce, p. 299 



282 



