172 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



of the flies, however, as in the mosquito and other midges, the 

 pupal stage is an active one although no food is taken during 

 it. The life history is usually rapid so that generation after 

 generation succeeds one another quickly. Thus it may be 

 true, as an old proverb says, that a single pair of flesh-flies 

 (and their progeny) will consume the carcass of an ox more 

 rapidly than a lion. 



About 50,000 species of Diptera are known, of which about 

 7000 occur in North America. The order includes the familiar 

 house-flies, flesh-flies, and blue-bottles of the dwelling and 

 stables; the horse-flies and green-heads that make summer life 

 sometimes a burden for horses and cattle; the buzzing flower- 

 ancl bee-flies of the garden; the beautiful little pomace-flies 

 with their brilliant colors and mottled wings, that swarm 

 about the cider press and fallen and fermented fruit; the bot- 

 flies, those disgusting pests of horses, cattle, rabbits, rats, 

 etc.; the fierce robber-flies that prey on other insects, including 

 their own fly cousins; the midges that gather in dancing swarms 

 over pastures and streams; the black-flies and punkies, vexers 

 of trout fishers and campers, and worst of all, the cosmopolitan 

 mosquitoes, probably the most serious insect enemies of man- 

 kind. A number of the specially injurious kinds of flies are 

 described in Chapters XXVIII and XXX to XXXVII. 



Order Siphonaptera. The fleas are blood-sucking parasites 

 of birds and mammals which were long classified as a family 

 (Pulicidce) of the Diptera, being looked on as wingless and 

 otherwise degenerate flies. They are now, however, given 

 the rank of an independent order. Nearly two hundred species 

 of fleas are known in the world, of which about fifty occur in 

 North America. Only a few species have been found on birds, 

 the others on mammals, both domesticated and wild. 



The fleas are all wingless and have the body greatly flattened 

 laterally. The mouth-parts are composed of several sharp, 

 strong, piercing stylets and a pair of thicker grooved parts which 

 can be held together to form a sucking tube. While the adults 

 are more or less familiar the young are rarely seen. The larvae 

 are small, slender, white, footless, worm-like grubs which lie 

 hidden in cracks and crevices and live on dry organic detritus. 



