Insects and Human Health 539 



from breathing. The breathing tubes, which issue from the 

 eighth segment of the abdomen, are of varying lengths in 

 different varieties. In the Culex the tube is longer than in 

 either Anopheles or Stegomyia. The Culex in breathing or 

 feeding is usually head down and tail up. When it breathes, 

 the end of the tube projects slightly above the surface of the 

 water. It feeds near the bottom or sides of the pool. The 

 Anopheles is normally parallel to the surface in breathing and 

 feeding. 



The food of the larvae is made up largely of microscopic forms 

 of plant and animal life, as spores of algae, diatoms, protozoa, 

 and decaying organic matter ; and if other supplies fail, they 

 feed upon the eggs and larvse of their own kind. The larvae 

 in the distilled or filtered water will probably show you this 

 fact. 



The wigglers or larvce are quite active. Their manner of 

 locomotion is very interesting. When threatened by a hand 

 or other moving object, they wiggle quite rapidly to the bottom 

 of the pool. Although they are not as luscious morsels as the 

 pupae for fish or other predatory foe, they have their enemies 

 and need power to escape. The chief natural foes of larvae 

 and pupae are fish, especially goldfish and the top-minnow, 

 the water beetle known as the back swimmer or water boat- 

 man, the larvae of the dragon fly, and occasionally larvae of 

 other species of mosquitoes. 



The larvce, at first small, grow rapidly. Within two or three 

 days the first skin becomes too tight and inelastic. There is 

 formed a new skin and the old one is molted. Molting occurs 

 four times during the larval stage of development. ^ Each time 

 the color of the skin is darker. The intervals between molting 

 vary from two days to several. 



After eight days, if the weather and food conditions are favor- 

 able, the larva enters the pupal stage. The larva may develop 

 much more slowly, and in winter may continue in the hiber- 

 nating state. If you can find a pitcher plant with its water 



