LIFE HISTORY OF HYDROUS ( HYDROPHILUS ) TRIANGULARIS. 



19 



the body axis and closing the mouths of the air trunks. Fifteen to twenty minutes 

 is the length of time which usually elapses between successive intakes of air. 

 When the larva is resting, however, it frequently remains beneath the water for a 

 much longer period. On the contrary, when actively feeding, the larva often 

 comes to the surface and supports itself on water plants or something of the sort 

 in such a position that the tip of its abdomen can remain constantly out of water. 



FEEDING. 



The prey is caught entirely with the mandibles, which seize it like a pair of 

 forceps. While the larva moves about continuously in search of food, it can not 

 be said in any sense to chase its prey, but is content with whatever it happens upon. 

 Once within its grasp the prey is squeezed to death by the powerful mandibles, if 

 that be possible. The carcass is then manipulated between the antennas, the 

 maxillae, and the labium, being turned around, moved back and forth, and folded 

 and unfolded as if it were between the tips of four fingers and a thumb. Every 

 second or two the mandibles close down on it like a pair of scissors, mashing it, 

 cutting or rending it asunder, and cramming it down the throat all in one movement. 



When eating snails the procedure is somewhat different. The snail is seized 

 by the mandibles and the head is thrown backward until the snail touches the 

 dorsal surface of the thorax. It is then held between the head and thorax as in a 

 vise and is very quickly crushed and eaten. The outlets of the ponds at Fairport 

 had a cement wall on either side for 10 or 15 feet. These walls were often lined 

 with small snails just above the water's surface and made a favorite hunting ground 

 for the Hydrous larvae. The latter swim or crawl along just beneath the surface 

 until they see a snail. The head is then thrust above the surface and the snail 

 is grasped between the mandibles and torn loose from the wall. The larva then 

 reverses its body, the tip of the abdomen is thrust up into the air while the head, 

 holding the snail, is carried beneath the surface. After the snail is consumed the 

 larva reverses ends again and hunts for another. It sometimes happens that the 

 snail gets a chance to set itself upon the wall after it is seized. In such cases the 

 larva is often unable to tear it away and has to leave it and try another. But 

 occasionally, either through design or accident, it comes back and tries the same 

 snail again in a few minutes. 



Some of the authors mentioned have commented upon the skill with which 

 the larva extracts the snail from its shell. If the contents of the digestive canal 

 are any evidence, the larva seldom extracts the snail at all but simply crushes 

 the shell and swallows the shell fragments along with the body of the snail. 



FOOD. 



The accompanying table presents the results of the examination of the contents 

 of the alimentary canals of 52 Hydrous larvae. The lengths of the larvae are given 

 in millimeters, and they present a range in size from 20 to 61 mm., the last six in 

 the table being fully grown and ready for pupation. 



