74 NATURAL HISTORY OF AQUATIC INSECTS CH. 



the eyes assume their black colour. Then the tips 

 of the mandibles, the claws of the foot, and lastly the 

 head and thorax take a brown colour. The legs 

 darken, the pupal skin is torn open, and a dark- 

 coloured Beetle emerges, destined to live henceforth 

 in the water." 



Miger adds that the perfect Insect remains several 

 days underground before attempting to escape. At 

 length it forces a passage through the earth, being 

 aided by the flexibility of its wing-covers, and the 

 compressibility of its segments, which have not as yet 

 acquired any considerable degree of firmness. 



The adult Hydrophilus may attain a length of over 

 if inches, and a breadth of about half as much 

 (45 x 20 mm.). With the exception of the Stag- 

 beetle it is the largest British beetle. The elytra or 

 wing- covers are, like the rest of the upper surface, 

 of a dark olive green. They are marked with faint 

 longitudinal sunk lines alternating with rows of dots. 

 The male Beetle is distinguished by the last joint of 

 the tarsus, which is dilated into a triangular plate, 

 and is believed to serve as a clasper. The species is 

 not uncommon in stagnant water near London, and 

 in the southern counties. 



Hydrophilus often leaves the water by night, and 

 flies abroad. In winter it hibernates, burying itself 

 in the banks of the ponds which it inhabits. It is by 

 no means so powerful a swimmer as a Dytiscus. The 

 legs are less expanded, and are worked alternately 

 instead of simultaneously, so that the motion is 

 wavering and unsteady. The thorax and abdomen 

 are bevelled off to an angle on the middle line of the 



