344 



The Two-winged Flies 



larval skin, and issue as adults in ten or twelve days after birth. The blow- 

 flies and bluebottles, members of this subfamily, have the body steely blue or 

 greenish and are great buzzers. The blow-fly, Calliphora erythrocephala , 

 has the thorax black and abdomen steely blue. Its eggs are laid on exposed 

 meat, fresh or decaying, such egg-infested meat being called "blown." The 



FIG. 489. A blow-fly or flesh-fly, Sarcophaga sarracenia. 



indicated by line.) 



(After Lugger; natural size 



larvae feed on the juices of the decaying meat and pupate after a few days. 

 The pupa? enclosed in the thickened brown last larval skin look like 

 large smooth shiny brown elliptical seeds, as do indeed the pupae of all 

 Calyptrate Muscidae. The commonest bluebottle- or greenbottle-fly is Lucilia 



ccesar, which lays its eggs in 

 cow-dung as well as on flesh, 

 and which often comes into 

 houses, particularly before rain. 

 A flesh-fly of serious importance 

 is the terrible screw-worm fly, 

 Compsomyia macellaria, which 

 FIG. 490. Diagram of wing of Lucilia ca>sar, j ays j ts eR p S on fl es h manure, in 

 showing venation. , . . , 



open wounds, and often in the 



nasal passages of domestic animals and human beings, entering the nose for 

 this purpose while the unfortunate person or animal is asleep. Numerous 

 frightful cases of such attacks on persons are recorded, especially from the 

 southern states. The larvae fairly eat away the whole inner nose and upper 



