506 



DISEASES OF CATTLE. 



animals from buffalo gnats. The burning of smudges is also a useful 

 means of protecting stock from the attacks of these flies. 



SCREW WORMS.' 



_§iGrew^worms (fig. 4) are the maggots of a fly (Chrysomyia macel- 

 laria), so called from their fancied resemblance to a screw. The adult 



fix (fig- 5) is about one-third of an 

 inch long, with a bluish-green body, 

 red eyes, and with three dark longi- 

 tudinal stripes on the back (thorax). 

 Attracte d by odors of decay, it deposits 

 its eggs, 300_to 400 at a time, in cuts, 

 ^ores, castration wounds, etc^ TKe 

 crushing of a tick on the skin com- 

 monly results in screw- worm infection 

 at that point. The eggs hatch in a 

 few hours and the larvae or maggots, 

 or so-called screw worms, begin to bur- 

 row into the flesh and continue bur- 

 rowing and feeding from three to six 

 days, after which they leave the 

 wound and crawl into the earth, there 

 transforming into the quiescent pupal 

 stage. This stage is completed in three 

 to fourteen d ays . The mature flies then 

 emerge from the pupal envelope and are 

 soon ready for egg laying. From two to three weeks are therefore re- 

 quired for the entire life cycle, although under certain conditions it is 

 possible for the fly to undergo its full development in as short a time as 

 seven days, and on the other hand as long as a month is often required. 

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

 man. In the case of hogs it is gener- 

 ally the eai^s which are affected. The 

 fly also breeds in dead animals, and all 

 carcasses should therefore be buried 

 deeply or burned. The complete de- 

 struction of all dead animals by burn- 

 ing has been found by the Bureau of 

 Entomology to be by far the best method of controlling screw worms. 

 Treatment for screw worms. — For proper treatment an animal suffer- 

 ing from screw worms should be caught and thrown. Chloroform is 

 then poured into the wound, taking care that it penetrates thoroughly 

 into all the burrows of the screw worm, if necessaiy using a slender 

 stick or a small bunch of twisted hay as a probe. The animal should 



Fig. 3. — Buffalo gnat. Enlarged. (From 

 Bureau of Entomology.) 



Fig. 4.— Screw worm (larva of Chrysomyia 

 macellaria). Enlarged. (From Bureau of 

 Entomology.) 



1 For further information consult Farmers' Bulletin 857. 



