3 88 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



chapter, but it is harder to control the horn-fly because it 

 breeds in the cow manure all over the pasture. Various 

 repellent washes are recommended for use, but none is wholly 

 satisfactory. 



The screw-worm flies, Chrysomyia macellaria, often cause 

 great suffering on account of the habits of the larvae. These 

 gray-flies, as they are sometimes called, may lay a mass of three 

 or four hundred eggs on the surface of wounds on cattle, 

 horses, etc. The larvae which hatch from these eggs in a few 

 hours make their way into the wound and feed on the surround- 

 ing tissue. Slight scratches that might otherwise quickly heal 



FIG. 175. Blow-fly, Calliphora vomitoria. (Two and one-half times 



natural size.) 



often become serious sores on account of the presence of these 

 larvae. Many cases are on record of these flies laying their 

 eggs in the ears or nose of children or of persons sleeping out of 

 doors during the day. The larvae, burrowing in the mucous 

 membrane, cause terrible suffering and often death. 



The blow-flies, Calliphora vomitoria, the blue-bottle flies, 

 Lucilia spp., and the flesh-flies, Sarcophaga spp., all have 

 habits somewhat like those of the screw-worm flies. The 

 flesh-fly, instead of laying eggs, deposits living larvae upon 

 meat wherever it is accessible, and as these larvae grow with 



