TWO-WINGED FLIES AND FLEAS 103 



canal of vertebrate animals sheep, oxen, or horses, 

 according to the species in question. The female 

 sheep-nostril-fly, 1 for example, drops her eggs (or 

 perhaps newly-hatched larvae) into the nostrils of a 

 sheep. Growth and development take place in the 

 cavities of the head to which the nostrils give access ; 

 and ultimately the mature " bots," as the larvae are 

 called, fall to the ground, where they pupate beneath 

 stones or clods. The bots of warble-flies 2 live just 

 under the skin of oxen, and are the cause of serious 

 loss to stock-owners on account of the damage done to 

 the hides. Strangely enough, the adult flies of this 

 family are practically without mouth-parts, and take 

 no food of any kind. They are rarely seen except 

 when flying around the animals that they victimize. 



The enormous family Muscidce includes most of the 

 species that commonly visit the habitations of man- 

 kind the house-flies, flesh-flies, blue- and green- 

 bottles, not to mention many less familiar kinds. All 

 these feed, as maggots, on decaying animal and 

 vegetable substances, each species having its own 

 predilection and habits. One fly known as Stomoxys 

 calcitrans calls for special mention, because it is nearly 

 related to the dreaded tsetse-flies of the African 

 continent, and, like them, has piercing mouth-parts 

 (very exceptional endowments among the Muscidce), 

 with which it is able to suck blood. It is very much 

 like, and is often confused with, the common house- 

 fly ; 3 and as it rarely enters houses except before rain, 

 there is a popular belief that " flies begin to bite before 

 rain." Of course, the real house-fly, having only a 

 suctorial labium, never bites at all. Nevertheless, it 

 has been convicted of contaminating our food with the 

 1 (Estrus ovis. 2 Hypoderma. 3 Musca domestica. 



