214 FLEAS, FLUKES AND CUCKOOS 



heron louse-fly {Lynchia albipennis) was once taken off a purple heron. 

 In this country louse-flies are rarly if ever found on the bodies of birds 

 during the winter months but up to 50 per cent, of a population may 

 become infested in summer. The young are far more susceptible to 

 attack than adult birds. 



It is interesting to find that the geographical distribution of some 

 species does not depend entirely on the distribution of the host. The 

 common louse-fly in Britain has a distinctly southern distribution; 

 faither north it is replaced by the grouse louse-fly. The two species, 

 however, are difficult to distinguish and are often confused; further 

 information is required before defining the exact areas they occupy. 

 Like the fleas, the bird louse-flies spend a part of their life-cycle in the 

 nest, so they are not entirely protected from changes in cHmate. This 

 factor is probably the key to their respective distributions. 



Outside Britain a malaria-like parasite of birds [Haemoproteus] is 

 spread by the pigeon louse-fly (Pseudolynchia canariensis) . Since many 

 wild birds are infected with this disease in Britain it is highly probable 

 that our species of hippoboscids are also carriers of the disease. 



Mosquitoes and Gnats (Guligidae) 



Mosquitoes and gnats are smaU slender flies with long legs and an 

 elongated proboscis adapted for piercing and sucking (Plate XIIc). 

 If they are examined carefully the characteristic fringe of scales — often 

 rainbow-hued — on the veins and margin of the wings can be seen. " The 

 structure and make of the gnat," wrote one of the early naturalists, 

 "there is no man but may justly admire. For in that so small insect and 

 as good as none almost what reason is there ? what inextricable 

 perfection? . . . where his taste, where his smelhng? where is begotten 

 that terrible and great sound?" It nevertheless would have surprised 

 the writer to know how much print and paper has been devoted 

 to the mosquito since his day. Even the fall of the Roman 

 Empire has been seriously attributed to their agency, as carriers of 

 malaria. 



Mosquitoes are a fairly large group of which over 2,000 species have 

 been described — about 30 from Britain. They are found throughout 

 the world from the tropics to the arctic circle. The most important 

 genus as far as birds are concerned is Culex, although some species of 

 Aedes and Anopheles, both found in this country, wiU sometimes attack 



