MOSQUITOES AND FLIES 



in a small quantity of water, provided the latter contains 

 sufficient food material. 



The tip of the respiratory tube is furnished with five 

 small lobes arranged like the points of a star about the 

 central breathing hole. When the larva is below the sur- 

 face, the points close over the aperture and prevent the 

 ingress of water into the tracheae; but as soon as the tip 

 of the tube comes above the surface, its points spread 

 apart. Not only is the breathing aperture thus exposed, 

 but the larva is enabled to remain indefinitely suspended 

 from the surface film (Figs. 174 D, 181 B). In this posi- 

 tion, with its head hanging downward, it feeds from a 

 current of water swept toward its mouth by the vibration 

 of the mouth brushes. Particles suspended in the water 

 are caught on the brushes and then taken into the mouth. 

 Any kind of organic matter among these particles con- 

 stitutes the food of the larva. Larvae of Culex mos- 

 quitoes, however, feed also at the bottom of the water, 

 where food material may be more abundant. 



The body of the mosquito larva has apparently about 

 the same density as water; when inactive below the sur- 

 face, some larvae slowly sink, and others rise. But the 

 mosquito larva is an energetic swimmer and can project 

 itself in any direction through the water by snapping the 

 rear half of its body from side to side, which characteristic 

 performance has given it the popular name of "wiggler." 

 The larva can also propel itself through the water with 

 considerable speed without any motion of the body. This 

 movement is produced by the action of the mouth brushes. 

 Likewise, while hanging at the top of the water, the larva 

 can in the same manner swipg itself about on its point of 

 suspension, or glide rapidly across the surface. 



The larvae of Culex mosquitoes reach maturity in about 

 a week after hatching, during the middle of summer; but 

 the larval period is prolonged during the cooler seasons of 

 spring and fall. The larva passes through three stages, 

 and then becomes a pupa. 



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