230 FEESH-WATBE AQUAKIA. 



have no breadth to speak of. It is indeed the narrowest for 

 its size of all British insects. It is about iin. long and about 

 half a line broad ; its legs are wonderfully slender, and it is 

 of a dark slate-colour. The portion of its head in front of 

 its eyes is considerably elongated, and at the extremity of 

 this curious elongation rather long and very fine antennae 

 are inserted. The eyes are prominent, and the under-part of 

 the body has a hair-like covering. As Jff. stagnorum has no 

 wings, the easiest way to tell the perfect insect from the pupa 

 is to remember that the outer part of the body in the former 

 is hard and in the latter soft. The soft covering allows for 

 the necessary growth. To detect this curious creature, one 

 must look very closely at the surface of the water upon 



which it walks. It is found upon 

 both ponds and streams, and also 

 upon their adjoining banks. 



Of the genus Gerris, which 

 contains about ten species, 

 G. lacustris (Kg. 145) is the 

 commonest member. It is not 

 quite lin. long, of a dark slate- 

 colour, with yellowish marking 

 at the sides of the body. 

 FIG. 145. Gerris lacustris. O. Najas, the largest and one of 



the commonest species, can be 

 easily recognised by its great size, long legs, and want of 

 wings. It is found upon running water, and is very difficult 

 to catch in the net. The larva and the pupa of this insect 

 may be distinguished by the size of the abdomen. When the 

 former is just hatched, the abdomen is extremely small, but 

 it increases in size as the animal grows older. The legs are 

 very long from the first, and the full-grown G. Najas is 

 known by the faint signs of wings. G. thoracica is , smaller 

 and less common than the preceding Gerris, and may be 

 readily detected by a reddish mark upon the back of the 

 thorax; hence the specific name. G. gibbifera is of the same 

 size as G. thoracica, but is without the mark upon the thorax. 

 It is also a rather broader insect, and is more abundant. 



