1921] Riley: Responses of Water-Strider 281 
gestive paper by -Parshley (1917) is valuable because of its 
probable bearing on the phototaxis of aquatic Heteroptera. 
In one of my former papers (1919a, pp. 499-500), it has been 
pointed out that some of the genera in the family Belostomidz 
are positively phototactic at night to electric lights—street arc 
lights. Benacus griseus and Lethocerus americanus have been 
observed in great numbers flying around electric street lights. 
It is very probable that other aquatic genera and species of the 
order Heteroptera exhibit phototactic responses. A recent 
paper by de la Torre-Bueno (1920)—and the references con- 
tained therein—is suggestive because of the explanations 
it may offer regarding light responses of certain aquatic 
Heteroptera. 
IV. SUMMARY AND CONCLUSION. 
1. INTRODUCTION. 
This paper treats of some of the general responses of the 
large water-strider, Gerris remigis Say, one of the common species 
of aquatic Heteroptera, to contact and also to photic stimuli. 
According to de la Torre-Bueno (1911), its systematic position 
is as a member of the family Gerride, subfamily Gerrine, tribe 
Gerrini, and subgenus Aquarius Schell (=H ygrotrechus Stal). 
The optimum habitat of the species is, in the main, on the 
water-films of permanent brooks and creeks, of medium size, 
with currents of moderate velocity. The structural characters 
of the body, as well as the general behavior of the species 
appear to be suited for a life in such a habitat. The species is 
mainly an apterous one. 
2. DISCUSSION. 
Gerris remigis readily responds to contact, various objects, 
in its habitat, such as a piece of driftwood, a rock, a drifting 
leaf, and the bank of the stream serving as stimuli. Thig- 
motaxis is evinced by the members of this species coming to 
rest against such solid bodies. Contact between two individ- 
uals frequently results in a cessation of locomotion of both 
gerrids. Animals under the influence of contact stimulation 
remain stationary from a few minutes to an hour or more. 
