INSECTS AFFECTING MAN AND ANIMALS 387 



mouth-parts make a wound into which is injected poison from 

 the salivary glands. Animals are driven frantic by the 

 attacks of these pests and may even suffer death unless they are 

 afforded some protection. Considerable losses are occasioned 

 each year because of farmers not being able to work animals 

 in the fields during the season that these insects are flying. 

 The possible relation of these flies to pellagra has been referred 

 to in the preceding chapter. 



The larvae of the black-flies are aquatic, attaching themselves 

 to the surface of rocks in swiftly moving streams. It is 

 difficult to fight them there, but some small streams may be 

 cleared of their breeding places, or the water may be treated. 



FIG. 174. Screw- worm fly, Chrysomyta maccllaria. (Three times natural 



size.) 



with phinotis oil and many of the larva? destroyed without 

 injuring the fish in the stream. Dense smudges will keep the 

 adults away, and some protection may be afforded animals by 

 smearing them with cotton-seed oil or oil and tar. 



The horse-flies, gad-flies, breeze-flies and deer-flies, all be- 

 longing to the family Tabanida, can pierce through the toughest 

 skin and are often a source of great annoyance to live stock. 

 Some of them often attack man also. Cattle and horses 

 sprayed with some crude oil emulsion are not attacked as 

 freely as unsprayed animals. Laurel oil has recently been 

 recommended as a fly repellent. 



Horn-flies, H&matobia serrata, and the stable-fly, Stomoxys 

 calcitraus, are among the most serious pests of cattle. Means 

 for controlling the latter have been suggested in the previous 



