86 OUR INSECT FRIENDS AND FOES 



above the surface of the water, to take in a fresh 

 supply of air, is very similar to that of the Great 

 Water Beetle. It also has a curious habit of 

 rising to the surface and turning over on its 

 back, so as to cause the water-film covering the 

 under side of its body to burst and enable it to 

 respire freely. It will rest in this manner, upon 

 its back, drawing in the air, and then, turning 

 over, will once more plunge beneath the surface 

 of the pool, taking with it a newly formed 

 air-film on the underside of its body. 



In April, and again about the end of August, 

 the white silken cocoons filled with the eggs of 

 Hydrobius may be found in great numbers, 

 either floating at or near the surface, or loosely 

 attached to the submerged stem of some aquatic 

 plant. The minute larvae, directly they make 

 their escape from the egg, are extremely active 

 and predatory, and have large heads armed with 

 a pair of very formidable jaws, which they open 

 and shut in a most sinister manner. The larva 

 draws its supply of air direct from the atmo- 

 sphere by means of its tail, which has a sort of 

 shallow cup upon the dorsal surface formed by 

 a number of valves and flaps. As it always 

 frequents shallow water, it has little difficulty in 

 rising to the surface and sticking its specialized 

 tail out to draw in a fresh supply of air; and 

 while hanging thus head downwards from the 

 surface, it will move its body about in all 

 directions, seeking its prey. When full grown 

 it quits the water and digs a little globular 

 chamber in the moist earth, in which to pupate. 

 If these larvae are collected for the purpose of 



