234 Annals Entomological Society of America  [Vol. XIV, 
the air. When in this position the fore- and middle-legs are slightly 
bent so that the claws are at the surface. The insects often rest at 
the bottom, clinging to sticks or weeds. 
The contact phases of behavior of Gerris remigis that have 
been discussed are very suggestive of the responses of some other 
members of the Hexapoda, for example certain Agrionid nymphs, 
of the order Odonata, described several years ago in a paper by 
me (1912, pp. 274, 280), brief quotations from which follow: 
In their natural habitat, Agrionid nymphs react strongly to contact. 
They are found clinging tightly to the stems, branches and leaves of 
Fig. 2. Detail of portion of surface of brook-pool, with current passing through 
it—flowing to left—along margin of forested region, near White Heath, 
Illinois—autumn. Five water-striders, Gerris remigis Say, shown on surface- 
film in contact with solid objects and clinging to them; indicates manner of 
group formation. Water-striders, about one-third natural size. (For other 
details, see Fig. 3.) (Photograph by Lloyde and Riley.) 
Elodea and Ceratophyllum. This is an indication of their decided thigmo- 
tactic proclivities. They tend to place as much as possible of the external 
parts of their bodies in contact with a solid surface. This is accom- 
plished by clinging to the aquatic plants, in such a manner that the 
long axes of their bodies le parallel to the long axes of the stems and 
the branches. The nymphs frequently assume a somewhat different 
position, with the long axes of their bodies rather oblique to the long 
axes of the stems and branches. The creatures are frequently found 
with their bodies closely applied to the Elodea and Ceratophyllum at 
the points where the branches are given off—that is, in the forks formed 
by the stem of the main plant and the lateral branches. They are also 
