The Two-winged Flies 303 



ing and injurious pests of horses, cattle, raijbits, rats, etc.; the fierce robber- 

 flies that prey on other insects, including their own fly cousins; the midges 

 and gnats, that gather in dancing swarms over i)astures and streams; the 

 black -flies and punkies, dreaded enemies of the trout-fisher and camper; 

 and, worst of all, the cosmopolit/an mosquito, probably the most serious insect 

 enemy of mankind. Only in recent years have we come to recognize the 

 mosquito's real capacity for mischief. Annoying and vexatious they have 

 always everywhere been, by day and night, from tropics to pole, from the 

 salt marshes by the sea to the alpine lakes on the shoulders of the mountain- 

 peaks. But that the mosquito-bite not only annoys but may kill, by infect- 

 ing the j)uncturcd tissues with the germs of malaria or yellow fever or filari- 

 asis, three of the most wide-spread and fatal diseases of man — this alarming 

 fact is a matter which has come to be really recognized only recently, and 

 the general recognition of which has given to the practical study of in.sects 

 an importance which years of warning and protesting by economic entomol- 

 ogists have been wholly unable to do. 



The Diptera include about 7,000 known species in North America, thus 

 ranking among the principal orders of insects in degree of numerical represen- 

 tation in this country. About 50,000 species are known in the whole world. 



The order may be separated into certain principal subdivisions by the 

 following table: 



Living as external parasites on mammals, birds, or honey-bees; body flattened and 

 often wingless; the young born alive as larva; nearly ready to pupate. 



Suborder PuplPARA (see p. 351). 

 Not living on the bodies of other animals; young usually produced as eggs. 



Suborder Diptera cenuina (see p. 304). 



Antennx with numerous (more than five) segments. .Section Nematocera (see p. 304). 



Antennse with not more than five segments, usually with three, the third sometimes annu- 



lated, showing it to be a compound segment, i.e., composed of several coalesced 



segments Section Br.'^chycera (see p. 327). 



Third segment of antennae annulated, showing it to be composed of several coalesced 



segments (see p. 327). 



Antenna; consisting of four or five distinct segments (see p. 330). 



Antenna; with but three segments (rarely less), the third segment with or without a 

 style or bristle (see p. 332). 



Of the two suborders the smaller one, the Pupipara, including certain 

 strangely specialized and degraded parasitic flies, will be considered last. Of 

 he first suborder, the Diptera genuina, the various families of small midge- 

 and mosquito-like flies composing the section Xeinatocera (flies with slender 

 several-segmented antenna;) will be discussed first, as they are believed by 

 entomologists to be the more generalized or simpler flies. 



