THE FAUNA OF BIRDS* NESTS 249 



welcome guests, but there are several groups of Coleoptera which prey 

 on the parasites of the birds, especially fleas and their larvae, and can 

 therefore be regarded as symbiotic partners. Foremost of these are rove 

 beetles (Staphylinidae) and histerid beetles (Histeridae). The former 

 family is extremely interesting (see p. 50), since many species have 

 become adapted to life in nests — of colonial and gregarious insects as 

 well as of mammals and birds — all over the world. In this country the 

 genus Microglotta is the most noteworthy. The insects feed on fleas and 

 their larvae. It seems possible that the species in birds' nests such as 

 M. nidicola and M. pulla can only breed at a temperature between 36° 

 and 40°G. — in other words when the parent birds are brooding. 

 Although these beetles often remain in deserted nests and wander into 

 ants' nests, they apparently do not breed there and Heim de Balzac 

 suggests that high temperatures are necessary to bring about the 

 maturation of the gonads. In Britain M. nidicola is confined to nests of 

 the sand-martin and is found in about 70 per cent, of their burrows — 

 sometimes more than fifty specimens in one nest. Other species recorded 

 from this country are M. picipennis, apparently confined to buzzards' 

 nests in Britain, but found in those of a variety of birds of prey on the 

 continent, and M. gentilis, which favours owls' nests. 



A wide range of hosts seems suitable for M. pulla, which has been 

 recorded from the habitations of many birds, but shows a predi- 

 lection for those of tits. There are of course various other rove beetles 

 associated with birds' nests, of which perhaps Atheta nidicola and 

 A. nigricornis are the most characteristic. Although recorded from 

 martins' they are more commonly met with in other nests. Spittle has 

 found both in the nests of the heron and carrion-crow along with a 

 third species, A. trinotata, which unlike the previous pair is not pre- 

 dacious but parasitic upon anthomyid fly larvae and pupae. One 

 species, A. oloriphyla, was first found in 1933 in a swan's nest and has not 

 been recorded since. Other typical genera are Philonthus (P. fuscus 

 seems confined to birds' nests) and Aleochara. Of the Histeridae the 

 genus Gnathoncus is a voracious eater of fleas in all stages of development. 

 Curiously enough it is absent from the martins' nests, which have the 

 highest flea population known (see p. 109). It is possible that it has a 

 liking for certain species, e.g. the hen flea (C gallinae)^ but not for others. 

 A wide variety of nests harbour G. punctulatus, (see tail-piece Chapter 7) 

 and in Finland it is a constant and sometimes dominant species in the 

 nests of the house-sparrow, great tit and similar birds which are usually 



