THE INSECT WORLD. 



333 



The larvae are commonly known as "wrigglers," and are of 

 two general types, — one usual in Culcx and its allies in which the 

 head is held down in the water and the tail or anal siphon is kept 

 at the surface ; the other peculiar to Anopheles, in which the body 

 rests for its full length on the surface. 



All the larvcC breathe through a single spiracle at the end of 

 the anal tube or siphon, and most of them must come to the 

 surface at rather short intervals to secure the necessary supph' of 

 air. When startled they make their way through the water by a 

 peculiar jerky or wriggling motion, which gives them their com- 

 mon name. 



Eggs are laid in \arious ways : sometimes singly on water or 

 on vegetation in water, or in damp places where water is likely 

 to come ; sometimes they are laid in masses, forming ' ' boats, ' ' 

 which float on the surface of the water, and this is the habit of 

 our most common sj)ecies. Under proper conditions the eggs 

 hatch quickly and the larvae develop in accordance with the 

 temperature ; a week or ten days being sufficient to carry the 

 insects from it'g^g to adult in midsummer. 



The larva must have water for its development, but there is 

 none so foul and none so salt that some species does not breed in 

 it. There is no space here for methods of dealing with these 

 pests ; but measurable exemption froni annoyance may be secured 

 by a free use of the oil of citronella on exposed parts of the body. 



Mosquitoes occur all over the world, and they are quite as 

 numerous and troublesome in the arctics as they are in the tropics. 

 \\\ fact, the climatic peculiarities of parts of the frigid zone, giving 

 a short hot summer over a surface soaked with water from meltino- 

 snow, produce conditions which favor their development in great 

 nunil)ers. In permanent ponds or streams their natural enemies, 

 of which there are many, keep them down to insignificant numbers. 



Closely resembling mosquitoes in appearance are the Chiro- 

 nomidcs, which may be recognized by the naked wings and by 

 having the thorax produced so as to hide the small head from 

 above. The antennae are feathered in both sexes, those of the 

 male strikingly plumose. To this family belong the gnats or 

 midges which may sometimes be seen dancing in swarms in the 

 evening only a few feet above ground, generally early in the 

 year and in damp places. The larvae are mostly aquatic, and 



