72 CULICID^ [CH. 



Flight. Although long flights have been recorded in isolated 

 cases, there is little doubt that as a rule the flight of mos- 

 quitoes is very limited, rarely exceeding a quarter of a mile. 

 From a prophylactic point of view, the distance they are 

 capable of travelling is of great importance, for in most coun- 

 tries it is only possible to keep circumscribed areas free from 

 mosquitoes, and if the insects were able to travel any con- 

 siderable distance these areas would be continually invaded by 

 mosquitoes from the surrounding country. It is known that this 

 does not happen to any marked degree, but occasionally long 

 flights have been recorded suggesting that under some con- 

 ditions the Culicidae may travel considerable distances. The 

 majority of such flights seem to be of a migratory nature and 

 the cause of them is unknown. The most authentic accounts 

 all come from America, where the salt-marsh species belonging 

 to the genus Aedes are certainly capable of travelling five to 

 ten miles, whilst distances of as much as 40 miles have been 

 recorded. Such flights, however, must be regarded as very 

 exceptional and, from a prophylactic point of view, may be 

 disregarded. 



Enemies. In the section on the methods of destruction 

 of these insects, we shall have occasion to refer again to some 

 of the natural enemies of the mosquitoes. The greatest 

 mortality takes place amongst the immature stages, which 

 are exposed to the attacks of countless enemies. In fact the 

 observations of Nicholls and others have shewn that the larvae 

 of mosquitoes are practically unable to exist in permanent 

 waters, as the latter contain such large numbers of predaceous 

 aquatic animals, such as fish, dragon-fly larvae, beetles, etc. 

 The importance of fish in destroying larvae is now generally 

 recognized, but unfortunately in many cases it is rather difficult 

 to employ this means of destruction, as the mosquitoes can 

 breed in small pools of water where fishes cannot live. 



The bladder-worts, Utricularia, capture various animals in 

 their small bladders, and in this way considerable numbers 

 of the larvae may be destroyed, as the plants will grow in 

 stagnant pools. In addition another insectivorous plant, 

 Aldrovanda vesiculosa, a member of the sundew family, captures 



