MODES OF FEEDING 153 



descend — seeking their food along the bottom and being obliged to come to the 

 surface for air. The larvge of Anopheles nonnally remain at the surface. They 

 lie with their bodies extended straight and locked to the surface film by the 

 chitinous flaps surrounding the sessile breathing-tube and by the stellate tufts 

 of the abdominal segments. When they move they do so in very rapid jerks, 

 either along the surface, or, when alarmed, descending into the water. When the 

 Anopheles larva is at rest its body is always extended in a straight line and this 

 gives these larvae a curiously rigid appearance which is very characteristic. The 

 head is very motile and in feeding its ventral side is usually turned upward, 

 while the mouth-brushes, in constant vibration, produce a current which brings 

 floating particles to the mouth. 



The larvae of other mosquitoes progress through the water with a peculiar 

 snake-like motion, most marked in the species with the longest bodies, such as 

 Aedes calopus and Aedes trtseriatus. The movement is a lashing one ; the body 

 is bent in the shape of a letter " S " and lashed from side to side. Certain larvae 

 can also be seen, at times, progressing merely by the action of the mouth-brushes. 

 In the former case the larva progresses through the water backwards, in the 

 latter case it moves head foremost. 



The larvae of many Culex and Aedes feed mostly while suspended from the 

 surface film by the end of the breathing-tube, obtaining their food by the action 

 of the mouth-brushes. Other larvae feed at the bottom and only come to the 

 surface at intervals to obtain air, this interval differing with the species. Some, 

 indeed, never rise to the surface and obtain the necessary oxygen from the water 

 by osmosis, or, in the case of Mansonia, from the vascular roots of aquatic plants. 



The attitude, when suspended from the surface film, differs with the species. 

 TJranotcenia maintains a horizontal body-position and this, together with the 

 similarity in the shape of the head, produces a resemblance to Anopheles which 

 has often proved deceptive. The larva of Culex territans holds its body in a 

 nearly horizontal position when suspended from the surface film, but the long 

 perpendicular breathing-tube and the broad deflexed head give it a characteristic 

 appearance. Other species suspend themselves with their bodies at more or less 

 of an angle. In certain species of Aedes the body hangs nearly straight down. 



Certain larvae feed altogether at the bottom and only come to the surface at 

 long intervals. Such is the case with many species of Aedes. Wyeomyia and 

 other sabethids are bottom feeders and are busy most of the time working over 

 the rubbish at the bottom of the breeding-places ; they seem to require but little 

 air and never remain suspended from the surface film for any length of time. 

 The larvae of certain species of Culex lie upon the bottom back downward, 

 anchored, so to speak, by a pair of hooks at the tip of the breathing-tube ; the 

 head is somewhat deflexed and the large mouth-brushes procure the food ; they 

 rise at intervals for air. Psorophora discolor has a larva of very similar habits ; 

 however, it never comes to the surface, procuring oxygen from the water by 

 means of the highly developed anal gills. 



The predaceous larvae can not be said to hunt their prey. They remain 

 quiescent until a larva comes within reach when they seize it with great rapidity. 



