216 ALLIED MUSCID AND MLSCELLANEOUS FLIES 



The anterior spiracular processes (fig. 93^) are yellow in colour 

 and have thirteen lobes. 



The Moth Flies. Psvchoda spp. 



There may be found frequent!}^ on window panes small, grey, 

 moth-like flies known as " moth flies " or " owl midges." The 

 wings of these minute insects are large and broad in proportion to 

 the size of the body and are densely covered with hairs; when the 

 insect is at rest the wings slope in a roof-like manner. The larvae 

 of some species breed in excrement ; Newstead (1907) has found 

 the larvae in human excrement; others occur in decaying vegetable 

 substances. I have bred them from rotting potatoes, while certain 

 species breed in water, especially when it is polluted with sewage. 

 Such aquatic species have the spiracular apparatus modified to 

 suit their changed life. Welch (1912) has recently described the 

 life-history of a new species, Psychoda albimaculata, which was 

 found breeding in the sewage and water of the experimental tanks 

 of the Chicago sewage works. Although a form, Fhlebotomus, 

 which occurs in southern Europe, northern Africa and north India, 

 has blood-sucking habits, most of the species" are of little economic 

 importance in their relation to man except in their role as 

 scavengers. 



Among other species of flies which occur in or visit houses 

 may be mentioned the Cheese Maggot Fly, Pmphila casei L., 

 whose larva the well-known " cheese skipper " lives in cheese, 

 ham and other animal substances, usually of a decomposing 

 chai'acter. The life-history of this species may be passed in so 

 short a time as three weeks, or it may be more prolonged. Occa- 

 sionally the larvae may be more responsible for cases of intestinal 

 myiasis. The flesh-flies, of which group Sarcophaga cavnaria is 

 a common species, occasionally^ occur in houses. They breed in 

 excreta and decomposing animal matter, especially dead insects. 

 The Yellow Dung Y\y, Scatophaga stercoraria L., a rather large 

 yellow fly which is commonly found on and breeding in cow dung 

 and other excreta, is found in country houses on rare occasions. 

 Reference has already been made (p. 171) to the useful character 



