TWO-WINGED INSECTS 379 



The maggots in cherries are the offspring of the Cherry Fly (Trypeta 

 cerasi), a small insect with brown bands on the wings. 



A fly very similar in appearance to the house fly is known as the 

 Stinging Fly (Stomoxys calcitrans). It annoys men and cattle on warm 

 sultry days by the painful stings (see gnat) which it inflicts, its favourite 

 place for settling on being the calves of the leg. 



The Gad Fly (Tabanus bovinus) and its allies are still more formidable 

 blood-suckers, selecting chiefly cattle for their attacks. Cattle become 

 alarmed on even hearing the hum of this insect, and run about frantic, 

 with their tails in the air. 



Neither of these species is to be compared with the Tsetse Fly 

 (Glossina morsitans) of East Africa, which by its stings spreads a 

 contagion which destroys cattle to such an extent that cattle-rearing 

 becomes impossible in districts where this fly occurs. 



In our latitudes also occur a number of flies which are a veritable 

 scourge to cattle. 



One of the most formidable is the Ox Warble Fly (Hypoderma bovis), 

 which somewhat resembles a humble-bee. This fly, as well as another 

 species (H. lineatum) which is more common in England, lays its eggs 

 singly in the hair on the backs of cattle. The maggot when hatched 

 burrows into- the skin, and causes a large tumour called a warble, in 

 which it lives and grows. The tumour opens to the exterior by a small 

 aperture through which the maggot obtains air. The maggot remains 

 in the tumour for ten or eleven months, when it is full-grown. It ulti- 

 mately drops to the ground, where its development is completed. 



A closely related species is the Sheep's Nostril Fly (CEstrus oris), 

 the larva of which lives parasitically in the cavities of the nostril and 

 frontal bones of the sheep. 



In the stomach of the horse a disgusting kind of maggot is often 

 found attached by means of oral hooks, like a tape-worm (which see). It 

 is the larva of the Horse Bot Fly (Gastrophilus equi), which glues its 

 eggs to the hairs of the breast, neck, or fore-legs of horses. In con- 

 sequence of the resulting irritation the horse licks off these larvse, which 

 thus find their way into the intestinal canal. When they have reached 

 maturity they leave their host with the fasces. 



Sub-Order 2: Gnats (Nematocera). 



The Common Gnat (Culex pipiens). 



(Length about £ inch.) 



The gnat — apart from its long, plume-like antenna and other details 



of structure — as closely resembles the house fly as two members of the 



