April-June, 1920 Bulletin Brooklyn Entomological Society 67 



ETHOLOGICAL REMARKS ON SOME NEW ENGLAND 

 WATER-STRIDERS (HEMIPTERA). 



By H. M. Parshley, Smith College, Northampton, Mass. 



The college pond at Northampton is narrow and winding, 

 perhaps a mile long, formed by a dam thrown across a small and 

 rocky stream. For the most part its insect population is very 

 meager, due no doubt to an extreme lack of aquatic vegetation, 

 but at the upper end, where the stream forms boulder-strewn 

 rapids as it enters the pond, there is a numerous population of 

 aquatic Hemiptera, an association of water-striders which, as 

 I have observed on other occasions as well, seems characteristic 

 of such an environment. Investigating this company of navi- 

 gators on August 22, 1 91 9, I found the following species repre- 

 sentated: of the Gerridse — Gerris conformis Uhl., Metrobates 

 hesperius Uhl., Trepobates pictus H.-S., and Rheumatobates 

 rileyi Bergr. ; of the Veliidse — Rhagovelia obesa Uhl. 



These species are entirely confined to the surface, except the 

 last mentioned, which dives occasionally ; and they are quite 

 independent of aquatic vegetation, since for their prey they 

 depend very largely upon terrestrial insects which chance to fall 

 into the water and are borne down by the current. On the 

 occasion under consideration the individuals of Gerris con- 

 formis remained for the most part in schools under the shelter 

 of the bank, while those of Rhagovelia obesa, nymphs of perhaps 

 the fourth instar, formed a small, compact swarm in the eddy 

 behind a boulder. The other species were to be found scat- 

 tered more at large over the surface; but farther down, where 

 the water becomes quiet, all were entirely absent. Thus it ap- 

 pears that under certain circumstances these species afifect 

 running water by preference, although some of them, members 

 of the Halobatinge, may often be found on bodies of water quite 

 lacking in current, as stated by de la Torre Bueno.^ In order to 

 maintain their position near the foot of the rapids, these insects 

 ordinarily row in leisurely fashion against the current, thus ex- 

 hibiting like many other fluviatile animals what has been called 



1 Gerrids of the Atlantic States. Trans. Am. Ent. Soc, Vol. 37, ipn, 

 P- 243. 



