142 MISC. PUBLICATION 631, U. S. DEPT. OF AGRICULTURE 



to escape from the unsuitable breeding medium. Cases of ocular 

 myiasis are known. 



Literature. — The literature on the housefly is voluminous. A good 

 general work, which is more recent than Hewitt's well-known book, is 

 Austen (6) and its somewhat abbreviated revision, Austen (7). 



The Family TIPULIDAE 



The Crane Flies 



Members of this family are slender, very long-legged flies, with a 

 many-segmented antenna and a rather primitive wing venation. An 

 outstanding feature is the prominent V-shaped suture, the apex point- 

 ing backward, on the mesonotum, in place of the usual transverse 

 suture. In the typical tipulids ocelli are lacking, and there are two 

 anal veins that reach the posterior margin of the wing. Most mem- 

 bers of the family are of medium to rather large size. 



Cases of intestinal myiasis supposedly due to larvae of unidentified 

 members of this family have been recorded. 



The Family PSYCHODIDAE 



The Moth Flies 



These are small flies, rarely exceeding 4 mm. in length. The wings 

 are broad, often pointed, and are clothed with hairs or scales; when 

 at rest they are usually folded rooflike over the back. The costa is 

 continued around the margin of the wing; cross veins, when present, 

 are limited to about the basal third of the wing ; two or three of the 

 longitudinal veins are forked. Ocelli are absent. 



Larva. — The larvae are chiefly aquatic or semiaquatic, although 

 there are exceptions, notably Flebotomm. They are elongated and 

 cylindrical or somewhat flattened dorsoventrally ; the head is distinct; 

 the body segments are each divided secondarily into annuli, usually 

 two for each thoracic and the first abdominal, and three for abdominal 

 segments 2 to 7; certain of the annuli may possess sclerotized dorsal 

 transverse bands. Respiration is through a pair of anterior spiracles 

 and a single posterior respiratory tube. 



The Genus PSYCHODA Latreille 



The wing (fig. 84, A) is ovate-lanceolate, the veins and sometimes 

 the membrane clothed with hairs but not with scales; there are two 

 unforked veins (r 4 and r 5 ) between the anterior forked vein (r 2+ s) and 

 the posterior one (m^), and 3 unforked veins (m 3 , cu ± , and cu 2 + 

 2nd A ) behind the latter ; vein r 5 ends in the pointed wing apex. The 

 antennae are 14 to 16 segmented, the first 13 being subglobose, the re- 

 maining 1 to 3 segments small. 



Larva. — The larva (fig. 85) is more or less cylindrical and, when 

 mature, is several times as long as the adult ; the body is grayish white, 

 and the integument is covered with pale flattened hairs or scales, some 

 of which have dentate margins. The antennae are very short; the 

 respiratory tube slender, the lobes at its tips small. 



Taxonomy. — The taxonomy is difficult. The important characters 

 found in the wing venation, antennae, and male genitalia cannot well 



