INSECTS IN THE WATER 318 



them a small bubble of air. The film which encloses this 

 stretches from the tip of the wing-cases to the hinder 

 end of the abdomen. Many other aquatic beetles and 

 bugs have their bodies covered wholly or in part with 

 fine, velvety hairs, which entangle sufficient air for the 

 trachea? to perform their function while the insect is 

 submerged. The water-skaters are hairy all over ; and 

 when they dive, they are completely surrounded by an 

 air-bubble. But the great black water-beetle ( Hydrophilus 

 piceus) is downy only on the under surface of its body, 

 and when submerged carries its air-supply like a silvery 

 breastplate. The manner in which this insect replenishes 

 its store of air without leaving the water is very re- 

 markable. The terminal joints of its antenna? are broad 

 and hairy, and serve as little ladles, by means of which 

 small air-bubbles are dragged down and added to the 

 supply beneath the body. 



In the larva of Dytiscus all but the last two spiracles 

 at the extremity of the abdomen are obsolete ; and when 

 the insect requires a fresh supply of oxygen, it rises to 

 the surface, and thrusts the tip of its tail into the atmos- 

 phere. Among water scorpions and their allies (Nepidce) 

 a similar arrangement is in force ; but the body terminates 

 in a pair of grooved appendages, which can be pressed 

 closely together so as to form a long tube, through which 

 air is conveyed to the spiracles. The larva of a gnat 

 is also furnished with a breathing tube, which springs 

 from the last segment but two of the abdomen ; while the 

 pupa has two trumpet-like tubes on the prothorax. But 

 the most extraordinary respiratory appendage of this 

 kind is possessed by the so-called " rat-tailed " maggots. 

 These are the larva? of the drone-fly (Eristalis tenax). 

 They feed in liquid filth, or shallow pools of stagnant 

 water, and have long telescopic "tails," that can be 



