The Ecology of a Sheltered Clay Bank 239 
telling how many species have already become extinct 
through this agency during the existence of the clay 
bank. 
(C) RELATION OF POPULATION TO ENVIRONMENT, 
(a) Relation to Temperature. 
Insects know not dates; May or December, June or 
January mean nothing to them other than heat or cold. 
The insects’ calendar is the thermometer. Instead of 
saying that all the spring Hymenoptera, regardless of 
species, emerged during the latter part of June, I should 
say that they emerged when the average mean tempera- 
ture for fifteen days reached 73°. Let us not forget that 
June has nothing in its makeup to mean anything to the 
Hymenoptera, but 73° for fifteen days at the springtime 
of the year means to them life, sunshine and food. 
My attention was first attracted to this phenomenon 
in noting that in 1918 the life appeared from the clay 
bank about a month earlier than in 1917, and in 1920 © 
they appeared at almost the same time as in 1918. In 
other words, the hymenopterous life about the place 
was in its spring fullness on June 25, 1917, May 28, 1918, 
and May 30, 1920. The average mean temperature for 
the fifteen days preceding and including June 25, 1917, 
was 73 1/25°; the average mean temperature for fif- 
teen days preceding and including May 28, 1918, was 
73 4/25°; and for the same period preceding May 30, 
1920, was 731/2°. These temperature figures of course 
are only relative; the clay bank was facing the eastern 
sun, whereas, the temperature records were made in the 
shade; let us remember, too, that the life potential buried 
in the clay bank was likewise in the shade.* This corre- 
*The temperature records are from the U. S. Meteorological Re 
ports taken at St. Louis, twenty miles north of this site. 
