284 Annals Entomological Society of America [Vol. XIV, 
aquaria and also into the angles formed by the flanges and sides 
of the aquaria. They move into small spaces between stones, 
often staying there in a quiet condition for several days. These 
responses evidently are due to the thigmotactic proclivities of 
the gerrids. The tendency to congregate in compact masses is 
pronounced. 
The so-called death-feigning response can be induced in 
these animals by means of contact stimuli. Touching their 
bodies or stroking them, often is sufficient stimulation to incite 
the response. In some instances the gerrids can not be induced 
to feign death through the agency of contact stimulation. The 
bodies are rigid and the antenne and the legs are stiff while the 
response continues, the gerrids remaining motionless. At 
such times, contact stimuli may not arouse them from the 
death-feint, while on other occasions, such stimulation does so in 
a few seconds. Then again, there are instances, as the animals 
arouse from the death-feint, when the application of contact 
stimuli reincites the response. Vision appears to have little 
influence in bringing about the death-feigning response, but 
contact seems to be the principal factor in inducing it. 
During rain and wind storms, these water-striders leave the 
open, exposed surfaces of streams. They are found with their 
bodies in close contact with solid objects, such as rocks, vegeta- 
tion, banks of streams, and dams of driftwood. Usually, they 
are observed on the windward side of the objects that have been 
enumerated. If they are nearer to the leeward than to the 
windward side of a stream, during a wind or rain storm, they, 
generally, move to the former side. Frequently, they crawled 
from the surface-film onto these objects, many of them moving 
into crevices. Sometimes, they congregated by the hundred in 
such situations as have been mentioned, their bodies being 
in close contact with the substrata. Evidently, these responses 
are due to the thigmotactic proclivities of the animals. After 
the abatement of a storm, they again moved onto the surface- 
film. Some, promptly, ‘‘sought” the surface of the water, 
others after a few minutes delay, while still others did not reach 
the water-surface for a half an hour after the storm had ceased. 
Many of those that moved onto the surface-film last came from 
depressions and interstices in the substrata. Probably, they 
were influenced more strongly by contact stimuli than was 
