Insects and Human Health 541 



deposit her eggs. This she does three or four times during her 

 life. If the female is born late in summer, she may hibernate ; 

 in the succeeding season of warm weather she will revive and 

 proceed to lay eggs. 



Males and females are readily distinguished by certain struc- 

 tural features. The males have very long palpi, and a proboscis 

 which is not fitted for piercing. The antennae are covered 

 with fine hair, giving them a feathery appearance. Only the 

 females are able to bite, the proboscis being equipped with half 

 a dozen very fine, sharp, needle-like instruments that can pierce 

 the toughest skin. When these needles are thrust into the 

 skin and reach a blood supply, a quantity of saliva is injected 

 and then the blood is sucked up and ingested. 



The natural food of mosquitoes is not in any large measure the 

 blood of men or other animals. There are extensive regions 

 where mosquitoes abound and warm-blooded animals seldom 

 wander. It seems certain that only a small number of mos- 

 quitoes have the opportunity of banqueting on the blood of 

 human beings. Those that do succeed are likely to produce 

 more eggs and oftener, because of their superior diet. 



Because plant and fruit juices are the natural food of mos- 

 quitoes, it is supposed that the salivary secretion poured by the 

 insect into the food before being swallowed renders it easier to 

 suck and also prepares it for digestion. The plant juices may 

 coagulate and harden unless mixed with the saliva. When 

 mosquitoes feed on men and animals, they inject a quantity of 

 saliva into the wound, whether necessary or not. Some of it 

 is undoubtedly taken up again with the food ; but part is slowly 

 spread by the circulation of the blood and causes the irritation 

 and swelling experienced by many persons. 



Distribution. The Culex mosquito is very widely distributed 

 geographically ; but it is always domestic, that is, closely asso- 

 ciated with human habitation. Its habitual breeding places 

 are usually provided by human carelessness, and are such as 

 old cans, pans, bottles, barrels, neglected watering troughs, 



