CHAPTER VIII 

 NATURAL ENEMIES AND PARASITES 



Flies, which are such insidious and pertinacious 

 persecutors of man and beast, are themselves the prey 

 of innumerable enemies ; many species are much 

 sought for by birds, they are devoured by lizards 

 and toads, and they are equally preyed upon by 

 predaceous insects. Those flies which have bodies 

 with banded colours, and which otherwise somewhat 

 resemble bees and wasps, probably escape being the 

 victims of some birds ; but the tribe of flies does not, 

 like the beetles, the lepidopterae, and some other 

 insects, furnish instances of other common protec- 

 tive devices, such as bearing and voiding offensive 

 secretions, or attempted concealment in repose by 

 mimicry of environment. 



All insectivorous birds are fond of a diet of flies, 

 and we may largely attribute the spring-time immigra- 

 tion of the beautiful swallow tribe to the fact that 

 in the northern parts of the temperate zone swarms of 

 soft bodied dipterous insects abound, and there re- 

 place the hard cased and more chitonous insects of 

 hotter countries. The true swallow, the house martin, 

 and the sand martin, all require a special food for theii 

 nestlings; and they also then require the longer 

 summer days and the prolonged twilight of our 



