INSECTS MOLESTING FARM ANIMALS 277 



Horse-flies (Family Tabanidae) develop in moist soil or 

 mud, usually in the beds of reedy brooks and ponds. One 

 finds the larvae (fig. 77) among the roots of aquatic weeds 

 and grasses by lifting these from the water. The annual 

 crop of flies matures in midsummer. The males sip nectar 

 and plant juices, and are short-lived; the females bite 

 fiercely and suck the blood of all the larger hoofed mammals. 

 They are troublesome only by day. When fully mature 

 they lay their eggs on the' vertical stems and leaves of aquatic 

 plants, just above the surface of the water. Many handsome 

 flies (see fig. 118) are found in this group. 



The bot-flies (Family Oestridae) are parasitic 



as larvae. Three are notable and dangerous: 



one in the alimentary tract of the horse, 



causing various derangements; one in the 



frontal sinus of the sheep, causing vertigo to 



Fl fly 1 of 9 'ttehorse" the animal and often killing it ; one under the 



i ( 5by d M e r n s B j a H" ski* 1 on the backs of cattle, causing great lumps 



cTTsfo 4 /™ that may be readily felt by running one's hands 



Manual for the over an an i ma i' s back. These larvae (known 



seci5) ' as "ox-warbles") are the easiest of the bots to 



observe. Over each of them is a hole in the skin, out of which 



the larva will emerge when grown. When approaching the 



time of emergence (best in the spring) it may be brought to 



light prematurely. By placing one's thumbs at either side 



of the lump and pressing hard, the warble may be made to 



pop out through the hole into the daylight. 



The horse bot-fly is most easily observed of the adult 

 insects. It often follows teams along the highways or about 

 the fields, and its presence may be suspected from the 

 frenzied action of the horses, flinging their heads upward. 

 The bot-fly does not bite; it merely seeks to attach its eggs 

 to'the hairs about the front legs and shoulders of the horse, 

 within reach of his mouth. But the horse instinctively 



