2l8 FLEAS, FLUKES AND CUCKOOS 



Owing to its great economic importance the group as a whole has 

 been intensively worked, and a vast literature has grown up around it. 

 Unfortunately mosquitoes have proved difficult insects to study. Three 

 hundred years ago Thomas Mouffet summed up the situation satis- 

 factorily : " The distinction of gnats," he wrote, "is very perplex and 

 obscure and has puzzled all the philosophers." 



Black-flies (Simuliidae) 



The so-called black-flies, which are not always black, contrast with 

 mosquitoes in a number of ways. They are smaller and dumpy, with 

 short legs, and the female bites only by day. The larva and pupa, how- 

 ever, are similarly aquatic but they mostly inhabit swift running streams 

 with highly aerated water and not stagnant pools. 



The group contains approximately 500 species of which about 20 

 are British. Unfortunately very little is known about their blood- 

 sucking habits in this country and much of the available information 

 comes from observations made on similar species abroad. 



The majority of species of black-fly attack mammals, but some con- 

 fine their attention to birds, while a few bite both types of host indis- 

 criminately. The best known bird black-fly in Britain, which is confined 

 to the south and south-eastern parts of the country, is Simulium venustum. 

 It will swarm on the heads and rumps of sitting hens and turkeys and 

 drive them off their nests, and it will also force its way under the wings 

 of young birds and suck their blood — sometimes with fatal results. The 

 bite of the black-fly is much more painful than that of mosquitoes and 

 its saliva decidedly toxic. At times they are responsible for the death of 

 large numbers of cattle in eastern Europe. In America S. venustum is the 

 carrier of a malaria-like parasite {Leucocytozoon) of wild ducks which it 

 occasionally transmits to the domestic variety with fatal results. 

 Another species is the vector of an allied Protozoan from the turkey. 

 As Leucocytozoon is widespread among British wild birds (see p. 169) it is 

 highly probable that black-flies are also carriers in Britain. 



Only the female black-fly bites. The males are smaller and easily 

 distinguished by their greatly enlarged eyes which almost meet on the 

 top of their heads. Whereas the male mosquitoes attract the females by 

 a communal dance, the male black-fly actively seeks his mate and is 

 thus frequently found on or near the host. In some cases copulation 

 takes place in nooks and crannies on the body of the mammal or bird 



