1920) +: Riley: Responses of Water-Strider 265 
9. CONTACT RESPONSES AND RAIN STORMS. 
These water-striders frequently display a form of behavior 
that is at least associated with the contact response. During 
heavy rains, it has been found, in observations of their behavior 
on the surfaces of brooks and creeks, that they stride along the 
surface-film to the shore, to rocks, to dams formed of driftwood, 
and also to vegetation (Figs. 2, 3).. On one of the earlier occa- 
sions when responses of this character were noticed, work was 
being carried on along the course of a small brook, in the 
vicinity of White Heath, near Urbana, Illinois. A sudden 
thunder shower came up .and it was observed, as the rain 
began to fall, that the gerrids quickly left the open situations 
on the surface of the brook. Many of them sought the windward 
bank of the brook, at points where it overhung the water. 
Here they were found close in to the shore, usually, with the 
middle and hind legs on one side of the body anchoring them 
to the solid substratum. Others ‘‘sought’’ the windward 
sides of rocks where they attached themselves in a similar 
manner. In a few cases, it was noticed that they climbed 
up the perpendicular sides of the rocks and crept into crevices. 
In some other instances, they crawled up onto the upper 
surfaces of flat stones that were just a few inches above the 
surface of the water. Others came in contact with aquatic 
and semiaquatic plants that either extended above the surface 
of the water, or else grew along the margins of the brook (Figs. 
2,3). In this connection it may be of interest to direct atten- 
tion to a statement by Essenberg (1915a, p. 398), made with 
respect to Gerrits orba, who remarks that: 
When disturbed while on the water, the insects betake themselves 
quickly to the land or among the weeds, and hide by clinging to the 
lower surface of the leaves or by lying quietly on the ground. 
Near the location where my work was being done on that 
particular day, there was a large dam formed of driftwood, so 
situated that during this storm one side of it was to windward. 
It was found that the gerrids were congregated here by the 
hundreds.. Many of them were on the surface-film with their 
middle and posterior pairs of legs of one side placed on a portion 
of the driftwood. Such a position anchored them from the 
storm and gave them security from the wind and rain. Some 
left the water and crawled a few inches onto the driftwood, 
where they were secure. Their legs were spread out and their 
bodies flattened against the substratum. In a number of 
