THE ANIMAL PARASITES OF CATTLE. 



521 



Buffalo Gnats. 



These small flies, also known as black flies, are about one-eighth of 

 an inch long and have a characteristic •'humped*' back (fig. 8). 

 They breed in running water and appear in swarms during spring 

 and summer, often in enormous niunbers, causing great annoyance to 

 stock and human beings, on account of their bites and their entrance 

 into the eyes, nose, mouth, and other openings of the body. Their 

 bites appear to be poisonous and in seasons especially favorable to 

 the gnats heavy losses of horses and cattle often occur. 



Bufi'alo gnats are more troublesome in bright, sunny weather than 

 when it is cloudy, and animals which have not shed their winter 

 coats suffer more from their attacks than those with smooth coats. 

 Cattle kept in darkened stables are not molested. The application 

 of one of the fly repellents already 



mentioned (p. 518) will help to X7^x 



protect animals from buffalo gnats. 

 The burning of smudges is also a 

 useful means of protecting stock 

 from the attacks of these flies. 



Screw Worms. 



Screw worms (fig. 9) are the mag- 

 gots of a fly {Chrysomyia marel- 

 laria), so called from their fancied 

 resemblance to a screw. The adult 

 fly (fig. 10) is about one-third 

 of an inch long, with a bluish-gi-een 

 body, red eyes, and with three 

 dark longitudinal stripes on the 

 back (thorax). Attracted by odors 

 of decay it deposits its eggs, 300 

 to 400 at a time, in cuts, sores, cas- 

 tration wounds, etc. The bursting of a tick on the skin commonly 

 results in screw-worm infection at that point. The eggs hatch in 

 a few hours and the larvie or maggots, or so-called screw- worms, 

 begin to burrow into the flesh and continue burrowing and feeding 

 from four to six days, after which they leave the wound and crawl 

 into the earth, there transforming into the quiescent pupal stage. 

 After this stage has lasted for one to two weeks, the mature fly 

 appears. From two to three weeks are therefore required for the 

 entire life cycle. 



Besides cattle, the screw-worm fly attacks sheep, horses, hogs, and 

 man. In the case of hogs it is generally the ears which are affected. 



Fio. 8. — Buffalo gnat. (From Bin<^au 

 of Entomology.) 



