406 



ANIMAL BIOLOGY 



of warmer climates is frequently a serious human pest because the 

 female flea burrows into the skin when ready to deposit eggs. The 

 Cat Flea, Dog Flea, and House Flea we usually consider merely a 

 nuisance, but they are potential carriers of disease-producing 



Fig. 256. — Ox Botfly, Hypoderma lineata. A, eggs attached to hair; 

 B, larva; C, larva just beneath air-hole in skin of Ox; D, adult. 



microorganisms. One might think that a life devoted to the study 

 of fleas and lice could be more profitably spent, until we recall that 

 expert knowledge of these animals was essential to discover that 

 Trench fever in the World War was transmitted by lice; was es- 



Fig. 257. — Dog Flea, Clenocephalus canis. A, larva in cocoon; B, pupa; 



C, adult. (From Howard.) 



sential to make clear that Bubonic plague, or 'Black Death,' 

 is carried by fleas. (Fig. 257.) 



It was long known that rats die in great numbers during a plague 

 epidemic, and accordingly biologists set out to determine whether 



