404 THE NUDIROSTRIA. 



many other species of this tribe which^ like it, are in 

 the habit of walking more or less upon the surface of 

 the water. Most of the specimens of this insect are 

 entirely destitute both of wings and hemelytra, but 

 occasionally perfectly winged individuals are met with. 

 This variable occurrence of the wings is common to 

 this species and to the numerous Bugs of the genus 

 Gerris, commonly known as Boat-flies, from their 

 habit of skimming along upon the surface of the 

 ^vater by the aid of their long legs. These insects 

 are of a much stouter form than the Hydrometra, 

 and the lower surface of their bodies is entirely 

 covered with a beautiful silky down, which usually 

 appears silvery in certain lights, and serves to protect 

 them from the water. Their fore-legs are of moderate 

 length, but the intermediate and posterior pairs, espe- 

 cially the former, are very long and slender, and it is 

 by the aid of these that the Gerris is enabled to run 

 upon the surface of the water, for although the mo- 

 tions of the insect have no small resemblance to the 

 rowing of a boat, the feet in reality never sink below 

 the surface. Several species of this curious group 

 may be found in profusion upon every pond and upon 

 the still parts of rivers amongst aquatic plants. The 

 Velia currenSj a still stouter insect, with shorter and 

 stronger legs, has much the same habits, but is slower 

 in its motions, and generally frequents the margins 

 of streams. They are all predaceous in their habits, 

 sucking the juices of small insects, which they seize 

 with their fore-legs; they will also feed upon dead 

 insects, and when hard-pressed for food, will attack 

 the weaker individuals of their own species. 



