158 
Psyche 
[December 
The peak of the population had been reached during the 
third week in August when the pond was literally covered with 
D. americanus, together with a few specimens of another species, 
D. hornii. They remained on the deeper parts of the pond in 
schools well away from the bank, where they were moderately 
active and not easily alarmed. As the season advanced they split 
into more or less compact groups which spent more and more of 
their time near the shore. On October 4, there were two groups 
remaining. One, including a few individuals, drifted about the 
outlet; the other, a larger group, gathered on a shallow spot 
about a stump on the western edge. At this time there were a 
few specimens of Gyrinus scattered about also but on October 
eighteenth no beetles were visible. A week later two individuals 
were found widely separated. On November first, no insect life 
was visible about the pond except a few black flies. After the ice 
had formed beetles were found in the mud but none were resus- 
citated. 
The first appearance of D. americanus in the spring of 1925 
was during the latter part of April, several weeks after the first 
signs of insect activity. As may be seen from the accompanying 
table, it is evident that Dineutes leaves hibernation somewhat 
later than the Hemipterous back-swimmer of the genus Notonecta. 
Date 
Air Water 
Mud 
Prec. 
Weather Time 
March 28 
11 °C 12}/2°C 
11°C 
0.18 
Showers 2 p. m. 
April 3 
U%°C 10°C 
9°C 
0 
thin clouds 1 p.m 
One water strider and six back-swimmers observed. 
April 11 
11 C 12 C 
10 C 
0 
Bright 
2 :30 p.m. 
Back swimmers abundant 
April 23 
19°C 16°C 
12°C 
0 
Brigh 
12 m 
D. americanus first observed. 
It will be readily seen from these data that the temperature 
of both mud and water determin? the date of appearance. A 
few days late , April 25, Dineutes was active on several other 
ponds nearby in considerable numbers. 
