THE WATER-BEETLE. 351 



Properly speaking, it is an inhabitant of stagnant 

 waters, rather than of brooks ; but when a brook forms 

 a stagnant nook, where moss and mud are deposited, 

 that is a favourite spot for it, as larvae and insects are 

 always brought down by the current. It watches for 

 these with the greatest attention, and we have seen it 

 catching the larvae cases of the phrygancea, and shaking 

 them till it could get hold of the inmate, and plunging 

 into the mud after those of the ephemera. It is a very 

 indiscriminate devourer, and will attack not only its 

 insect neighbours, but the very young tadpoles of frogs, 

 and fry of fishes ; nor is it confined to animal food, for 

 we have seen it catch small crumbs of bread before they 

 reached the bottom, with so much apparent relish, that 

 there was little doubt that it ate them. 



The young plunger has the elytra or horny covers 

 of its wings nearly transparent ; but as it gets to ma- 

 turity, they become of a deep olive green, inclining to 

 black. They have not the brilliant gloss of the elytra 

 of some insects, but they are very hard and strong, 

 and supplied with a kind of oil or varnish, by means of 

 which the water is repelled, and the insect kept con- 

 stantly dry. This beetle may easily be known from 

 the colour, and also from the margin of dull reddish 

 orange with which the body is surrounded, and which 

 has given it its specific name of marginalis. 



As is indeed the case with most insects, especially 

 those that inhabit the water, the economy of the plunger 

 is but imperfectly known. It has been stated that the 

 female encloses her eggs in a cocoon of coarse silk. 

 But we have never been able to find any teats or nip- 

 ples, similar to those found upon ordinary spinning 

 2 H 2 



