266 Annals Entomological Society of America  [Vol. XIV, 
instances, they crept into slight depressions and interstices in 
the driftwood and lay there motionless. It should be stated 
that the great majority of the gerrids did not leave the surface 
of the water and those that did do so occupied positions seldom 
more than a few inches away from it. Those individuals, that 
were caught by the wind and rain on the surface-film in situa- 
tions considerably nearer to the leeward than to the windward 
side of the brook, in the main ‘‘sought”’ the bank on the former 
side. It was noticed that a larger number of these crawled 
from the surface-film onto some solid substratum than was the 
case of gerrids on the windward side of the brook. During 
such storms, none or only a few of the gerrids may leave the 
surface-film, but always they are found anchored to, or in 
contact with some solid object, or else on the surface of the 
water in some unusually well protected situation. In this 
connection a statement by de la Torre-Bueno (1917a, p. 296), 
with respect to a related species, Gerris marginatus Say, is 
of interest. He remarks that: 
Unlike its larger congener remigis, it is a dweller in still waters by 
preference. Here at times it gathers in large numbers. In strong 
winds it hugs the shore, particularly if it blows that way. 
After the storm was over and the sun emerged, many of the 
water-striders promptly ‘“‘sought’’ the surface-film and con- 
tinued their usual forms of behavior. Others delayed making 
this movement for several minutes after the cessation of the 
rain. While still others were found in contact with some solid 
substance for a half an hour after the storm had ended. Many 
of those, which first moved onto the open areas of the stream, 
were gerrids that did not crawl upon any solid surface away from 
the water. The animals which crept into depressions and 
interstices, in the main, were the last to reach the surface-film, 
probably due to the fact that greater areas of their bodies were 
apphed to the substratum and, therefore, contact stimuli 
influenced them more strongly than the others which did not 
have such large surfaces of their bodies in contact with some solid 
surface. Contact stimuli appear to play a considerable role in 
responses of the character that have been described. Certainly 
they seem to have a decided effect in the cessation of the 
locomotor activities of the water-striders. Such stimuli not 
only appear to exert influence in bringing the gerrids to rest 
against some solid object, but also in their action in keeping 
them there for considerable periods of time. 
