1921] Riley: Responses of Water-Strider 251 
in mud—from holes on the land, filled in with dead leaves and 
drift debris left after floods, under the roots of trees, and from 
under compact masses of dead leaves (Figs. 5, 6, 7, 8, 9). 
There would be so many of them from one location that they 
scarcely could be held in two cupped hands. At such times it 
was noticed that they were very quiet, there being hardly any 
movement at all on the part of the gerrids. If they were 
taken from their winter quarters during a thaw, there was more 
movement than was the case during freezing weather. Occa- 
sionally, when their hibernating quarters were uncovered, the 
insects were almost overlooked, because they remained so 
quiet and in such close contact with the substratum and with 
each other. There was, in addition, another fact which 
increased the difficulty of finding them and that was the 
frequent similarity in color of the background to the color of 
the water-striders. It has been observed by me (1912, p. 275) 
that certain other semiaquatic Hexapoda, Agrionid nymphs of 
the order Odonata, exhibit somewhat similar responses. 
In general it may be stated that when hibernating water- 
striders were found, their bodies were closely applied to each 
other. Those on the periphery of the group were in close 
contact with their immediate physical surroundings on the 
one side and with the gerrids forming the inner portion of the 
cluster on the other side. Frequently, their legs were so 
inextricably entangled that on lifting up a few members of the 
aggregation, many others would be found clinging to them. 
Essenberg (1915a, p. 400) has recorded responses of a similar 
character with respect to a closely related species of water- 
strider, Gerris orba. In connection with certain of the 
statements made above, a: quotation from one of my own 
papers (1919, pp. 402-403), on some habitat responses of 
Gerris remigis, may be of interest: 
During hibernation, there is no question about water-striders 
remaining quietly in one place for a long period of time. But it must 
be recalled that the temperature is low at such times, and that they 
frequently seek dry situations. . . . The positive thigmotactic responses 
of these gerrids have been observed frequently during periods of hiber- 
nation. At such times they formed tangled masses, which were due to 
the water-striders crowding closely together. These facts were recorded 
in my field notes as early as the winter of 1912-1913. 
