OUTLINES OF ENTOMOLOGY. 95 



The singular " rat-tailed " larvre, often found in stagnant pools or 

 other foul water, produce hairy flies of the genus Eristalis. 



Bot-flies (GSsTRiD^;) are stout, hairy insects, much resembling small 

 Humble bees. The mouth parts are but slightly developed, and the 

 small antenna, hidden in little cavities in the very narrow face, seem, at 

 first glance, to be wanting. They are chiefly interesting from the habits 

 of the larvae, which live in the stomachs of horses, in the heads of 

 sheep, and on the backs and other parts of the bodies of cattle and 

 other animals, causing great suffering and sometimes even death to the 

 poor creatures infested. The Bot-flies of the horse (Gastrophilus equi, 

 Fabr.) lay their eggs on the horse's front legs or on the flanks or hips, 

 glueing them most firmly to the hairs. The Iarva3, which are hatched 

 very shortly, produce an irritation which induces the horse to bite at 

 those parts, and by this means they enter the mouth and make their 

 way into the stomach. There they attach themselves, by means of 

 mouth hooks, to the lining membrane, feeding on the mucus and diges- 

 tive fluids, occasionally penetrating to the muscular tissue, causing 

 much irritation and pain, and, when very numerous, producing danger- 

 ous fever and weakness. When full grown, the "bots" pass out with 

 the excrement and burrow into the earth, from which the flies issue in 

 six or seven weeks. The Sheep bot-fly (CEstrus ovis, Linn.) deposits its 

 larvre, already hatched, in the nostrils of the sheep, which immediately 

 work their way into the nasal cavities and frontal sinus of the head and 

 attach themselves to the walls, producing the disease known as " grub 

 in the head,' 7 from which sheep so commonly suffer and not infrequently 

 die. When these maggots are full grown they drop from the nostrils 

 to the ground, beneath the surface of which they transform. 



The Ox bot-fly (Hipoderma bovis, De Geer) is a similar, but larger 

 species, which causes tumors on the backs of cattle, usually laying its 

 eggs on parts which the creature cannot conveniently reach with its 

 tongue. The larvae, termed " warbles," burrow beneath the skin and 

 cause very disfiguring and painful swellings. 



The Tachina flies (TACHINID^E) are stout, dark-colored, bristly 

 flies, which deserve to be held in the highest estimation on account of 

 the parasitic habits of all the larvae, which feed in the bodies of nu- 

 merous destructive caterpillars and grubs, and greatly reduce thd 

 numbers of these pests. The small, oval, ivory-white eggs are laid, 

 sometimes singly, sometimes two or three in a cluster, on the back of 

 the caterpillar or other insect, often just behind the head, in order to 

 be safe from the jaws of the victim. These eggs adhere so firmly that 



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