ORDER VII. TWO-WINGED INSECTS, OR FLIES. 297 



Bot-fly (GEstms veterinus), which deposits her eggs under the 

 throat of the horse. The maggots then enter the mouth 

 of this animal, are carried into the stomach, and go through 

 the intestines like the former ones, producing the same ef- 

 fects. 



The Ox BOT-FLY (CEstrus bovis) is nearly one inch long, 

 has a yellow breast, with a black band across it, while the 

 hind body is white and yellowish red, covered with hair, 

 and resembling that of the bumble-bee. The female of 

 this insect, with its long, horny ovipositor, pierces the skin 

 of the ox or cow, generally on the back of the body, and 

 deposits therein her egg, which is hatched by the caloric 

 of the animal. The maggot, as soon as hatched, finds its 

 nourishment in the cavity where it was born, and, as it de- 

 velops, causes the skin to swell, forming a protuberance 

 like that caused by gall-wasps on plants, and finally pro- 

 ducing a running sore. In the month of May there may 

 frequently be seen on the backs of young cattle from four 

 to twenty such boils, each an inch thick, with an opening 

 from which flows a purulent discharge. These maggots 

 live about four weeks under the skin, when they come out 

 from their disgusting and filthy abode, fall to the ground, 

 change into pupae, and a week after are transformed into 

 the perfect fly. The female of this insect is so prolific that 

 a single one may infest a whole drove of cattle with its 

 eggs. 



The SHEEP BOT-FLY (CEstrus ovis) has transparent wings 

 spotted at the lower margin, a brown spotted hind body, 

 with yellow and brown lateral lines, sparingly covered with 

 hairs. This' insect does not show much inclination to fly 

 or to walk, and is very slow in its motions. The female 

 lays its eggs on the nostrils of sheep, whence the hatched 

 maggots creep into the frontal cavity, and there develop 

 until fully grown, when they come out, fall to the ground, 

 and change into pupae, in which state they remain about 



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