THE BLOW FLIES 253 



ous species and liable to carry intestinal diseases. Their 

 larvae as a rule feed in excreta or in decaying flesh, but 

 a bluebottle fly in a milk jug is no more dangerous 

 than a house fly in the same situation. 



Liicilia casar L. (Fig. 28) is a common and wide- 

 spread form, abundant in both Europe and North 

 America, and is one of several species of the shining 

 green or bluish flies commonly found about dead ani- 

 mals and different kinds of excreta. It is not ordinarily 

 found in houses, but may be driven in at the approach 

 of a heavy storm, just as is the case with the biting 

 house fly. On May 17, 1899, for example, a heavy 

 storm occurred about four p.m., and the next morning 

 twenty-eight specimens of this species were found to 

 have come into one of the rooms of my oflice. In 

 Europe L. ccesar is known as the '^greenbottle fly," and 

 is almost exclusively a carrion feeder. 



Calliphora erythrocephala Meig. (Fig. 29) is an- 

 other widespread species common to Europe and North 

 America. It is a large bluebottle fly of rather dull 

 color with black spines on the thorax. It is the com- 

 mon blow fly of Europe and is the species treated by 

 Lowne in his classic work on the anatomy of the blow 

 fly. Its larvce are indistinguishable from those of the 

 greenbottle fly. The eggs are laid on meat and dead 

 animals and even upon dead insects. The species is 

 unusual from the enormous number of eggs laid by a 

 single female. The Russian author, Porchinsky, re- 

 cords from 450 to 600 eggs from a single female. 

 Hewitt records the duration of a single generation as 



