FEATHER LICE I37 



after death, had seven Hce attached to the inside of the webs of some of 

 the left wing feathers, and eight in a similar position on the right wing, 

 making fifteen in all. The bird was wrapped in a piece of cloth and two 

 hours later immersed in chloroform fumes to kill the ecto-parasites. 

 When it was shaken out over a piece of white paper, eight of the lice fell 

 out and one louse-fly {Ornithornyia fringillina) ; the remaining seven lice 

 were found clinging to the abdomen of the fly. These seven lice must 

 have attached themselves to the fly after the death of the host, using it 

 as a lifeboat for escape in the emergency. If the louse-fly in such 

 circumstances finds another starling, the lice are saved, but as the fly is 

 less host-specific than the Mallophaga, they must often find themselves 

 transferred to a different species of bird, on which they die, probably 

 from starvation — the lifeboat has transported them to a desert island. 



Other opportunities for lice to pass to hosts of a different species are 

 not frequent under natural conditions. The lice of brood parasites 

 such as the cuckoo have already been discussed. Another normal 

 association is that between predator and prey, and hawks and owls are 

 sometimes found harbouring a few lice, which could only have come 

 from a recently eaten victim (Plate VI). Such stragglers probably do 

 not survive long. Dust baths may be another method by which lice are 

 transferred, for where chickens and sparrows use the same dust baths, 

 the latter on examination have been found with a few specimens of 

 chicken lice. In captivity and under domestic conditions there are 

 naturally frequent occasions for lice to pass to new hosts. 



Lice do not normally leave the living bird and they are only rarely 

 found away from their hosts, except in the nest where they have been 

 seen crawling over the eggs and in the nesting material. 



Some of the factors which prevent establishment on a new host, even 

 if the difficulties of transport are overcome, have already been discussed, 

 (p. 1 24) . These include the physical structure of the feathers which may 

 make the movement, clinging, feeding and egg-laying of the louse 

 difficult or impossible, the chemical composition of the blood and 

 feathers which may be lethal, and the temperature differences which 

 may affect the development of the eggs and nymphs of the strange 

 louse. Apart from these factors, the immigrant louse must face the 

 competition of the normal louse population already well established 

 and better adapted to the environment on its own host. Furthermore, 

 the establishment of an immigrant louse species on a new host naturally 

 requires the presence of individuals of both sexes or a fertilised female. 



