156 
Psyche 
[December 
NOTES ON THE BEHAVIOR OF DINEUTES 
AMERICANUS 
By Howard B. Smith, 
Los Angeles, California. 
A study of Dineutes americanus carried on in the vicinity of 
Boston, Mass, during the past two years has led to some in- 
teresting results which are briefly presented in the present note. 
Recent papers (’23, Wilson, C. B.; ’25, Hatch, M. H.) have dealt 
with the life history and ecology of this beetle and the following 
observations serve to clear up certain points not included in the 
accounts of these authors. Among the several families of water- 
beetles, the Gyrinidse show more peculiar adaptations in structure 
and, consequently, in behavior and mode of life. 
Movement : — These beetles swim by means of the meso- and 
metathoracic legs, which are so modified as to be almost useless 
for land locomotion. While on the water D. americanus exhibits 
perfect mobility and ease in swimming, on land it turns to an 
awkward crawl, pulling itself along by the long forelegs, tilting 
from side to side as the heavy unsupported body is dragged 
across the uneven ground. Usually, however, when off the water 
surface, the body is supported only by the front legs. 
When about to swim the beetle extends the middle and hind 
legs laterally, like a pair of oars They are then brought smartly 
down to the caudal axis, which is their usual position at rest. 
The forelegs are fitted into the grooves in the sternal plate adapted 
to receive them or they may be extended on the surface film. 
Sometimes they are used for cleaning the body or to assist in the 
process of feeding. Because of the grooves in the sterna the legs 
can be withdrawn and the body then presents a perfect “stream- 
line” form. When alarmed the insect dives rapidly, carrying a 
small silvery bubble at the abdominal tip. 
Several experiments were undertaken to test the ability of 
Dineutes to swim in media other than water. A beetle was 
placed on the surface of 50% alcohol. It could not remain on 
