THE FLIES THAT CAUSE MYIASIS IN MAN 149 



is present in most members of the family and which is rarely found 

 elsewhere is the spurious vein, a veinlike fold in the membrane between 

 veins r 4+5 and m 1+2 , and transversing the cross vein r-m. The venation 

 is reduced from the type found in such families as the Sylvicolidae, 

 Stratiomyidae. Asilidae, and Therevidae, but not so much as in the 

 muscoids; the anal cell is always long but is closed before the wing 

 margin. 



Larva. — The habits of the larvae vary. Many are carnivorous, feed- 

 ing particularly on aphids but also on other Homoptera; some are 

 plant feeders; many species are scavengers. Some of the scavengers 

 have symbiotic relations with termites and social Hymenoptera, 

 whereas others occasionally become accidental parasites of man and 

 animals. 



Literature. — Useful summaries of the role of Syrphidae in myiasis 

 of man and domestic animals have been published by Hall and Muir 

 {51), Hall (SO), and by Metcalf (89, pp. 207, 217-219). 



The generic descriptions included in this work will, in general, dis- 

 tinguish the genera discussed here from others in the Holarctic Region. 

 For keys to the adults consult Curran's "North American Diptera" and 

 Lindner's "Die Fliegen der Palaearktischen Region;" for larvae see 

 Johannsen (62, pp. 22-2S) . A valuable and more recent work by Heiss 

 is not cited, because it does not include the rat-tailed species. 



The Genus SYRPHUS Fabricius 



This genus contains a number of species of familiar flies, the hover 

 flies, which are, for the most part, black or blackish, with prominent 

 yellow spots or bands on the abdomen. The larvae are carnivorous, by 

 far the greater part of their prey consisting of aphids. 



Austen (5) records three instances of supposed myiasis caused by 

 larvae of this or of the related genus Scaeva (as Lasiopticus) . In two 

 cases larvae were submitted by medical men as having been discharged 

 by patients through the rectum; in the third case a larva was removed 

 from the ear of a boy who had been troubled by pain and deafness in 

 that ear for 2 days. 



The occurrence of a larva within the ear was probably accidental, 

 and can hardly be regarded as myiasis ; the other records cannot be 

 accepted without substantiation. Any habits related to myiasis are 

 entirely foreign to members of this genus. Without doubt, larvae may 

 be ingested with brussels sprouts and other vegetables which in the 

 growing stage harbor colonies of aphids, but it is highly doubtful 

 whether they could cause enteric disturbances or pass through the 

 digestive tract alive. 



The Genus TUBIFERA Meigen 



This genus has commonly been known as Eristalis, and some workers 

 have applied the name Eristalomyia to tenox and related species. 



The adults are beelike in appearance, those of T. ten-ax resembling the 

 drone honeybee. The eyes are pilose; the face is tuberculate in the 

 middle; the epistoma is not produced; the antennae are short, the 

 third segment rounded or oval, with a dorsal arista. The thorax is 



