AQUATIC INSECTS 



family in our fauna, the other species being found in the 

 south. They stay about shallow pools, shut in by cat-tails 

 and overgrown with algal mats and duckweed where they 

 can be sure of a quiet place to prowl for their food (PI. II). 

 In order to find out what these measurers do it is necessary 

 to settle oneself comfortably in or near the pond since some 

 time elapses between their doings. Hungerford used to 

 keep watch on the pools, while seated on a three-legged stool 

 well out in the water. He saw Hydrometra spearing its food 

 in the water, capturing mosquito larvse and pupee, water 

 boatmen, and small crustaceans. 



Water-measurers lay their eggs from April through mid- 

 summer upon stems projecting just out of the water; they are 

 brown and spindle-shaped, with beautifully sculptured shells, 

 each one being fastened separately to the leaf. Hungerford 

 watched water-measurers laying their eggs on cat-tail sprouts 

 in April. Those which he kept in his aquaria placed their 

 eggs on the sides of the glass just above the water. line. 

 Length of adult, about half an inch. 



Broad-shouldered water stridors, Family Veliidae. — These 

 stout bodied animals are similar to the common striders, 

 GerridcE, in general appearance and habits. Like them they 

 are predator}^ and gregarious. The larger species belong to 

 the genus Rhagovelia which inhabits rapidly moving water. 



Fig. 172. — Broad-shouldered water strider, Rhag- 

 ovelia obesa, showing split in tarsus of middle leg. 



229 



