FLEAS 103 



Enemies of Fleas 



At all stages of its life history the flea no doubt has enemies. But 

 these have been imperfectly studied and it is not known how populations 

 of fleas are kept in check and whether their numbers are reduced by 

 parasites and disease. 



As an adult the flea's most important enemy is undoubtedly the bird 

 itself. Buxton has shown (p. 80) what large proportions are eaten by 

 their mammalian hosts. Birds are scrupulously clean and probably their 

 thoroughness in preening has forced their fleas to become nest dwellers. 

 In other words, only fleas which are to a certain extent pre-adapted to 

 a life in the nest can succeed as bird fleas. However, the nidicolous 

 existence exposes them to dangers from other animals occupying the 

 same habitat. Staphylinid and Histerid beetles have been observed in 

 nests catching and devouring fleas by the dozen. Ants also, if they 

 come into contact with fleas — which most often happens in old ground 

 nests — devour both the adult and larval stages. 



The sand-martin fleais particularly susceptible to a Gregarine (Proto- 

 zoan), a hyperparasite which is found in the mid-gut of larvae, pupae 

 and adults. Damp nesting sites favour the survival of the spores and the 

 reinfection of the flea, and for this reason between 65 and 100 per cent, 

 of the sand-martin flea population may be infested, but in the case of 

 C. gallinae the figure is steady at about 5 per cent. Its eflect on the 

 flea is not known. 



The plague bacilli can often prove fatal to the fleas which transmit 

 them, by multiplying in their gut and thus mechanically blocking the 

 proventriculus, when the flea starves to death. Certain roundworms, 

 apart from those which use fleas as intermediate hosts, feed on their 

 reproductive organs and can effect complete castration. 



A hymenopterous parasite, Bairamlia fuscipes, lays its tgg in the flea 

 larva and eventually kills it, during the course of its own development. 

 The only records from Britain are from squirrel and hen fleas. 



By far the most famous parasites of fleas are the mites which live 

 in the nest and destroy their larvae and pupae. There are numbers of 

 different species which inhabit both bird and mammal nests, and they 

 originally sprang into fame when Loewenhoek, over two hundred years 

 ago, first described them preying upon the larvae of the pigeon flea. 

 This discovery inspired the hackneyed but immortal lines : " Big fleas 

 have little fleas upon their backs to bite 'em." Hirst found that these 



