MUSCOIDEA: MINOR FAMILIES OF MUSCOIDEA 181 



this, enormous family can usually be distinguished from 

 MuscidcB by the bare arista and very bristly body. The 

 larvae live as parasites in the larvae of other insects, particu- 

 larly in the caterpillars of Lepidoptera, pupating in and 

 ultimately destroying their victims. The tendency of the 

 family is therefore beneficial, notwithstanding that certain 

 species sometimes destroy the larvae of useful insects. Some 

 few Tachinidce which have a long, pointed, chitinous proboscis, 

 might be mistaken for blood-suckers. 



Family Dexiid^ (^ef(o'? = nimble). The species of this 

 very large family resemble Tachmidce both in structure and 

 habits. Like TachinidcR they are very bristly, but usually the 

 arista is pubescent and the body and legs are elongate. 



Family CESTRID^, Bot-flies. (Lat. ffi'j^r«j=o?a-T/oo? = a 

 fly that drives to frenzy). The adults of this family are very 

 short-lived, and hence have the mouth small and the mouth- 

 parts vestigial or rudimentary. They attach their eggs to 

 the hairs of mammals, in which the resulting larvae are 

 parasitic — either in the stomach or intestine, or in the 

 pharynx and nasal passages and the contiguous sinuses, or in 

 the subcutaneous tissue. When the maggot is full grown it 

 leaves its victim in order to undergo pupation in the ground. 

 As a rule the larva of each species of fly has a preference for 

 one particular species of mammal. A good many species are 

 parasitic in domestic animals, and several of these may 

 fortuitously victimise man ; the species most known as a 

 human parasite is the " Macaw-worm " {Dermatobia noxialis) 

 of Tropical America. 



The flies are more or less hairy and bee-like, and have a 

 large head with a heavy, swollen, somewhat " underhung " 

 face ; the antennae and the wing-venation are much like those 

 of a Muscid fly, and the squamae are usually large. The 

 maggots are large and stout, and are ringed with many large, 

 recurved, dark-coloured spines. 



The four most common genera are the following : — 

 Gastrophilus. The larva lives in the stomach and intestine 

 of the horse, ass, and some other Ruminants. In the adult 

 fly the arista of the antennas is bare, the squamae are small, 

 and the 4th longitudinal vein runs straight towards the 

 edge of the wing, so that the ist posterior cell is widely 



