1921] Riley: Responses of Water-Strider 247 
In some of my own work (1912, pp. 283-285) on the behavior of 
Agrionid nymphs, of the order Odonata, it was observed that’the 
responses exhibited, during the process of the disassociation 
of groups, were decidedly of a lke nature to those of Gerris 
remigis. It was found that compact aggregations were formed, 
but that the Agrionid nymphs did not remain quiet for as 
long periods as either Ranatra fusca or Gerris remigis and that 
the breaking up of such groups was apt to occur at shorter 
intervals. The disassociation of these clusters resulted from 
mechanical stimuli and also from the activities of certain 
nymphs within the aggregations, although photic stimuli 
played a part in this process. The Agrionid nymphs in the 
peripheral portions of the groups were more likely to leave 
first, as those in the more central parts of the clusters were 
influenced more strongly by the contact stimul of the individ- 
uals surrounding them, and, therefore, frequently remained 
more or less stationary. 
5. CONTACT RESPONSES AND HIBERNATION, 
During the period of hibernation, responses to contact 
stimuli are strongly in evidence. Gerris remigis begins to 
leave the surface-films of streams in the early autumn, con- 
tinuing this migration until the late fall, and goes onto the 
land to “‘seek’’ winter quarters. The gerrids of this species 
hibernate in various situations. They have been taken from 
under piles of dead leaves, from interstices and deep holes in 
the banks of streams, from under tree-roots on the land, from 
under the bark in interstices of fallen dead trees, from holes 
in the ground under logs and driftwood, and from under piles 
of brush (Figs. 5, 6, 7, 8, 9, 10). They have been found, also, 
in such places as are mentioned by Kirkaldy (1899a, p. 151), 
who refers to the Gerridz in general in the following quotation: 
As has been previously remarked, many of the Gerride conceal 
themselves—in fact ‘‘hybernate’’—under moss, stones, etc., often far 
from water, during the winter. 
However, it should be stated that, after looking through my 
field notes for the past few years, no records were found of 
Gerris remigis hibernating far from water (Figs. 5, 6, 7, 8, 9). 
Further investigation may prove that alate forms (Fig. 11) 
of this species sometimes hibernate in other situations than 
