514 



DISEASES OF CATTLE. 



SCREW WORMS. 



back (thorax). 



Fig. 9. — Screw worm (larva of Cluy- 

 somyia maceUaria). Enlarged. 

 (From Bureau of Entomology.) 



Screw worms (fig. 9) are the maggots of a fly {Chrysom/yia mdcel- 

 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-green 

 body, red eyes, and with three dark longitudinal stripes on the 

 Attracted by odors of decay it deposits its eggs, 

 300 to 400 at a time, in cuts, sores, 

 castration wounds, etc. The crush- 

 ing of a tick on the skin commonly 

 results in screw-worm infection at 

 that point. The eggs hatch in a 

 few hours and the larvae or mag- 

 gots, or so-called screw worms, be- 

 gin to burrow into the flesh and continue burrowing 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. 

 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, although under certain conditions it is possible 

 for the fly to undergo its full de- 

 velopment in as short a time as 

 nine days. 



Besides cattle, the screw-worm 

 fly attacks sheep, horses, dogs, and 

 man. In the case of hogs it is gen- 

 erally the ears which are affected. 

 The fly also breeds in dead ani- 

 mals, and all carcasses should 

 therefore be buried deeply or 

 burned. 



Treatment for screw wonns. — 

 For proper treatment an animal 

 suffering from screw worms should 

 be caught and thrown. Chloro- 

 form should be poured into the 

 wound, taking care that it pene- 

 trates thoroughly into all the burrows of the screw worm, if necessary 

 using a slender stick or a small bunch of twisted hay as a probe. The 

 animal should be held for several minutes in order to insure the con- 

 tinued action of the chloroform. Instead of chloroform, gasoline may 

 be used. Finally the wound should be dressed with a carbolic or 

 cresylic ointment to promote healing and thus prevent further infec- 

 tion, or the wound may be painted with pine tar. Dipping in the 

 arsenical dips used for destroying cattle ticks is a convenient method 

 of treatment if many animals are involved. 



Fig. 10. — Scrcw-worm fly (Chrysomyia 

 maceUaria). Enlarged. (From lUiroau 

 of Entomology.) 



