WHAT WE SHOULD KNOW ABOUT MOSQUITO BIOLOGY 269 



of plant and animal life in the water, although certain species are 

 predaceous, and some are scavengers upon the dead animals and insect 

 life in their habitat. 



The larvae of mosquitoes are very peculiarly constructed. The mouth 

 is furnished with tufts of filaments which are constantly in vibration. The 

 head is large, the antennse long, the thorax somewhat swollen, and the 

 abdomen slender. The sides of the body are furnished with stiff bristles. 

 From the next to the last segment there protrudes a long tube neai'ly as 

 thick as the body itself, and it is this tube that touches the surface of 

 the water when the larva rises to breathe. When in this position the 

 larva ranges downward in various attitudes characteristic of the species. 

 The object of this tube is to get air. At the extremity is a breathing 

 hole, or spiracle, and into it run two main tracheae which extend through 

 the body of the insect with many branches which carry air to all parts 



Fig. 50. — Larva of the yellow-fever mosquito. Much enlarged. (Howard.) From U. S. 

 Dept. Agr., Office Secy., Cir. 61, fig. 14. 



of its tissues. The true anal end of the body is furnished with four more 

 or less developed tracheal gills. 



When suspended from the surface the wriggler's mouth parts are 

 constantly in vibration, bringing into its mouth any minute particles 

 which float in suspension in the water. 



It is when the larva extends its breathing tube from the surface of 

 the water that it offers the greatest opportunity for control. All efforts 

 to maintain an oil film on the surface of the water are aimed at clogging 

 up this tube when it comes to the surface, and thus cutting off the air 

 supply. 



Occasionally the larva descends to the bottom, jerkmg its body vio- 

 lentlv from side to side. The anal tracheal gills undoubtedly assist in 

 this motion. The larvte are active and move backward through the water 

 bv these jerky movements. They can move slowly forward by the action 

 of the mouth brushes. Some species are specially equipped for obtaining 

 air from the water or from plants and do not come to the surface. This 

 is fortunately not the case with those we are most interested in. 



Aedes argenteus larva (fig. 50) has the head rounded, widest behind 

 the eyes. The thorax is rounded, wider than long, with moderate, rather 



