360 MOTIONS OF INSECTS. 



which enables them to see readily and seize the insects that 

 fall upon the water, which are their prey. Sigara, how- 

 ever, a cognate genus separated from Notonecta by Fa- 

 bricius, swims in the ordinary way. As the Gyrini are 

 usually in motion at the surface, whirling round and 

 round in circles, it is probable that their legs are best 

 adapted to this movement. They dive down, however, 

 with great ease and velocity when alarmed. The com- 

 mon water-bug (Gerris lacustris], though it never goes 

 under water, will sometimes swim upon the surface, 

 which it does by strokes of the intermediate and pos- 

 terior legs a . These, however, are neither fringed nor 

 dilated, but very long and slender, with claws, not easily 

 detected, situated under the apex of the last joint of the 

 foot, which covers and conceals them. The underside 

 of their body as is the case with Elophorus, and many 

 other aquatic insects is clothed with a thick coat of gray 

 hairs like satin, which in certain lights have no small de- 

 gree of lustre, and protect its body from the effects of 

 the water. Some insects, that are not naturally aquatic, 

 if they fall into the water will swim very well. I once 

 saw a kind of grasshopper (Acrydium), which by the 

 powerful strokes of its hind legs pushed itself across a 

 stream with great rapidity. 



Other insects walk, as it were, in the water, moving 

 their legs much in the same way as they would do on 

 the land. Many smaller species of water-beetles, belong- 

 ing to the genera Hydrophilus> Elophorus, Hydrtena, 

 Parnus, Limnim> &c. thus win their way in the waves. 

 Thus also the water-scorpion (Nepa) pursues its prey ; 

 and the little water-mites (Hydrachna) may be seen in 

 * De Geer, iii. 314. 



