34 THE UNIVERSITY SCIENCE BULLETIN. 



noted, however, deal in large measure with their prowess in 

 mastering insects and other animals larger than themselves. 

 Thus the textbooks on Entomology state the the aquatic Hemip- 

 tera are without exception, predatory. We are led to believe that 

 those which dwell upon the surface lead a precarious existence, 

 subsisting upon such uncertain fare as the accidents of nature 

 may provide. In other words, that their food supply consists 

 in the capture of such flies and other terrestrial insects as may 

 chance to fall into the water. One writer in fact has stated 

 that Gerris shows no response to forms meeting the surface 

 film from below. This, however is not in keeping with the 

 frequent observation that Gerris will strike for a back-swim- 

 mer nymph that comes to the surface close by. 



The writer has pointed out that the food of our common 

 w^ater-strider Gerris marginatus consists at certain times of 

 the year almost exclusively of the Cicadellids (Jassids) and 

 related forms that feed on Juncus and spike rush, bordering 

 on and growing in the shallow waters. In checking over the 

 field notes on the feeding habits of these insects, it is seen that 

 much of their food is produced close at hand, both within and 

 about the pool. So, also, with the "toad-bug" Gelastocoris ocu- 

 latus, which has been taken feeding upon lace bugs (Tingi- 

 didse) reared close by. 



Our common species of Rheumatobates, while it does not 

 disdain to feed upon small insects that fall into the water, ob- 

 tains its main supply from the little crustacean forms such as 

 Ostracods and Daphnians which swarm the quiet pools. These 

 it captures as they rest at the surface, scooping them out and 

 holding them aloft upon the upturned tip of the beak, while the 

 body of the little victim is being depleted of its nutritive ma- 

 terial. 



The little Microvelia borealis, common in Kansas, has access 

 to the same source for its food supply and similar habits of 

 consuming it. Mesovelia mulsanti has been observed exploring 

 the sides of stems of rush and cattail that floated upon the sur- 

 face for Ostracods, which it occasionally obtained, while Hydro- 

 metra martini stalks about over the floating vegetation in 

 search of whatever small beings chance to come to the surface 

 film. Its victims have been observed to consist of mosquito 

 wrigglers, mosquito pupae, emerging midges, nymphal Corixids, 

 and Ostracods, as well as small terrestrial insects floundering 

 on the water. 



