MOSQUITO LARV.E 91 



hatched larvae. Almost invisible to the naked 

 eye, they are readily detected by the shimmering of 

 the water caused by their activity, and they rapidly 

 increase in size. Soon the larvae can be seen creep- 

 ing near the surface of the water. They finally 

 become J to J inch long, and swim about actively 

 in search of food. This they obtain from the organic 

 material in the water as well as from minute algae 

 and bacteria that are present. Though they are living 

 in water, air is a necessity, and the larvae come to the 

 surface to breathe. Like other less harmful insects, 

 some of the larvae are provided with air siphons in 

 their tails. The Culex that convey bird malaria 

 thrust their air siphons through the surface film of 

 water, and hang, head downwards, obliquely through 

 the water. The Anopheles that carry malaria from 

 man to man lie parallel to the surface, as they do 

 not possess long drawn-out siphons. This method of 

 breathing of the larvae is extremely important to 

 dwellers in the tropics, who can thus distinguish 

 between the Anopheles that may lead to their ill- 

 health, and the Culex, which may cause some slight 

 injury to their birds, but none to themselves. 



The early larval life of the mosquitoes is their 

 most vulnerable point. If they escape the effects of 

 chemicals on the water and the attacks of small pre- 

 daceous fishes to whom they afford dainty morsels, after 

 from eleven to twenty-one days depending on the 

 warmth and the food available each larva alters con- 

 siderably, and becomes a pupa. The latter is dis- 

 tinguished from the larva by its relative quietness 

 and by the development of a huge head. After a few 



