The Ecology of a Sheltered Clay Bank 247 
(c) Relation to cold, cloudiness, darkness. 
Up with the early morning sun, at 6:30 in fine weather 
the mining-bees of all three species, the carpenter-bees 
and the Monobia mud wasps were all heartily at work. 
They began early and worked diligently while the sun 
shone and then relaxed soon after midday as soon as 
the bank was in the full shadow. I have said elsewhere 
that these insects know no calendar but the thermome- 
ter; again we might well say they know no clock but 
the sunlight. I hope some day to find out just what is 
these bees’ program of daily work when their nests are 
in the normal light, i. e. not shaded by artificial struc- 
tures during any part of the normal hours of sunlight. 
While the action described above was their usual pro- 
gram, they sometimes made exceptions to this habit. 
These digressions I have been unable satisfactorily to 
explain. Often during the early part of June the An- 
thophora bees were seen at work at 5:30 a. m., and con- 
tinued busy until sunset. Despite the fact that May 28 
was cloudy, some 20 mothers were actively engaged in 
carrying in orange-colored pollen. On the other hand, 
When on June 16 the temperature dropped twenty de- 
grees, their activities were greatly lessened, and they 
did not venture out to resume their work until 9 o’clock 
on the 17th. Also after cold nights or rainy mornings 
and toward the end of the season, even when the sun 
did shine, often they did not come out early, but waited 
until the bank was thoroughly warmed up. Sometimes, 
when a run of cold days came in early autumn (in this 
detail I am speaking of the white-banded bees), they did 
not get out to work for two or three days; suddenly they 
Seemed to be seized by the impulse to work, and then 
