PARASITIC INSECTS 51 



lime or by tickling the inside of the nostrils with a feather dipped 

 in turpentine. 



The ox heel fly has still a different life history. The eggs 

 (Fig. 30, B) are fastened to the hair near the heels of cattle and 

 licked off as are those of the horse botfly. The larvae (Fig. 30, 

 C) act very differently, however. They bore their way through 

 the walls of the oesophagus and through the body, until after 

 about six or eight months they finally lie just beneath the skin 

 of the back, where they make a breathing hole through the 

 hide (Fig. 30, D). When full-grown, they are about two thirds 

 of an inch long; they then burrow out and drop to the ground, 

 where they complete their life history. The heel fly causes 

 losses of three kinds; first, loss in milk and flesh; second, damage 

 to hides from being punctured; and third, loss in trimming out 

 damaged meat from dressed carcasses. The loss of milk due 

 to these insects may be as high as twenty -five per cent; the loss 

 in flesh is estimated at from one to five dollars per animal; and 

 that to the hide at about sixty-five cents each. The entire 

 annual loss to the sixty million cattle in the United States, of 

 which about fifteen million are infested, is estimated at from 

 fifty-five to one hundred and twenty million dollars. The most 

 successful method of dealing with the bots is to remove them 

 one by one from the backs of the cattle by squeezing them partly 

 through the breathing pores made in the hide and then extract- 

 ing them with tweezers. 



Human beings may under abnormal conditions be attacked 

 by bots. There are a number of cases on record, but they are 

 so rare that no one need be afraid of becoming a victim. 



Fleas. — The flea is a degenerate insect with an extremely 

 small head and no wings. Unlike most of its relatives, its body 

 is very narrow and deep instead of broad and flat; this enables 

 it to glide easily among the hairs or feathers of its host. Its 

 legs are adapted for leaping, and the biting mouth parts of the 

 larva are adapted for feeding upon particles of decaying animal 

 and vegetable matter, Fleas are present on a great many kinds 



