370 AN INTRODUCTION TO ENTOMOLOGY 



the end of the abdomen. In fact, the legs are fitted for running over 

 the water, instead of for rowing, as with the Gerridee. The intermedi- 

 ate legs are about equidistant from the front and hind pairs, except 

 in Rhagovelia. These insects are dimorphic, both fully winged and 

 short -winged or wingless adults occurring in the same species. 



About twenty species of this family have been found in America 

 north of Mexico; these represent four genera. 



The broad-shouldered water-striders are found both on the banks 

 of streams and ponds and on the surface of water. About one-half 

 of our species belong to the genus Microvelia. These are very small, 

 plump-bodied bugs, which are usually black and silvery in color or 

 mottled with brown. They are found at the water's edge but run 

 out on the water when disturbed ; and they are also often found upon 

 rafts of floating vegetation. 



To the genus Rhagovelia belong somewhat larger forms, which are 

 characterized by the long, deeply split, terminal 

 segment of the tarsi of the middle legs. Our most 

 common species of this genus is Rhagovelia obesa 

 (Fig. 425). These bugs are found running over 

 the surface of rapidly moving waters in streams. 

 They can also dive and swim well under water. 



Four species of Rhagovelia are found in this „. „, ,. 



countr^^ 'fj^2' '''^'"'^*" 



The genus Velia includes the larger members 

 of the family. In these the tarsi of the middle legs are not cleft. 

 Four species of this genus occur in our fauna. They are found on 

 moderately rapid streams or little bogs and eddies connected there- 

 with. 



The fourth genus occurring in our fauna is represented by a single 

 species, Macrovelia harrisii, which is restricted to the Far West. 



Family GERRID.E 

 The Water-Striders 



This family includes elongated or oval insects which live upon the 

 surface of water. Their legs are long and slender; the hind femora 

 extend much beyond the apex of the abdomen ; the middle and hind 

 pairs of legs are approximated and distant from the fore legs; the 

 terminal segment of the tarsi, at least of the fore tarsi, is more or 

 less bifid, and the claws are inserted before the apex. The beak is 

 four-jointed. The antennge are long and four-jointed. 



The water-striders prefer quiet waters, upon which they rest or 

 over which they skim rapidly; they often congregate in great 

 numbers. There are commonly two forms of adults belonging to the 

 same species, the winged and the wingless; sometimes a third form 

 occurs in which the adult has short wings. 



These insects are predacious; they feed on insects that fall into 

 the water, and I have seen them jump from the water to capture flies 

 and other insects that were flying near them. 



