INSECTA: COLEOPTERA 



255 



The Larvae. 



spike may be to form an air channel from the air above, down 



to the eggs. It is, however, closed at the end, consequently 



air can only enter it by diffusion. The cocoon when finished 



is firm and watertight. 



The larvae, when they hatch, stay for about 

 twelve hours inside the cocoon, and then make 



their way into the water as soft grey- 

 coloured grubs, with black heads and 



strong jaws, with which they bite the 



animal food that they now favour — 



usually small snails and tadpoles. They 



have to come to the surface to breathe, 



taking in air through spiracles at the end 



of the tail. They grow very quickly, 



and in a few weeks, if well fed, the larva 



leaves the water and pupates in the earth, 



inside an oval cell which it excavates. 



The perfect insect when it emerges from 



the pupa remains underground for a day 



or two, and then forces its way out of the 



earth and flies to a pond. Except for 



occasional migrations from one pond to Fig. 186.— Larva of the 



another, it spends the rest of its life in 



the water, lying dormant at the bottom 



of the pond during the winter. 



The " Whirligig " or " Shiner " beetles are 

 classed with the Clavicorn beetles, since their 

 antennae are short and slightly club-shaped. 

 They occur in great numbers in ponds, especially 

 in the early autumn. The beetle is only 

 about \ of an inch long, and its body is 

 convex above and flat below. It has a 

 remarkably shining blue-black body, and 

 it darts about in the sunshine at the 

 surface of the water with great rapidity, 

 constantly turning and twisting, and so 

 earning the name of "Whirligig." If 

 disturbed, it swims to the bottom of the 

 water and clings to the weed, until it is 

 obliged to float to the surface again for 

 swims, a shining bubble of air is often 



Silver Water Beetle. 

 (After Miall,) 



(Natural size.) 



The 

 Whirligig 



Beetle 

 (Gyrinus). 



Fig. 187.— The Whirli- 

 gig Beetle {Gyrinus 

 natator). x 3J. 



more air. As it 



