224 Trans. Acad. Sci. of St. Louis 
their numbers was easily noticeable. On October 3, 
none at all were abroad, but of course at this date prac- 
tically all of the life on the bank was still. 
In 1918, when the carpenter-bees, the Anthophora 
mining-bees, and the caterpillar wasps all appeared a 
month earlier, about May 25 (because of temperature 
conditions), these Chalcid parasites too appeared a 
month earlier. All of the life in the bank responded to 
the same laws. In 1918 these parasites were just as 
numerous but I was surprised to note no increase over 
the previous year. It would have seemed reasonable 
to expect that the myriads of the last year would have 
multiplied as greatly, at the expense of everything else, 
that this year there would be little or nothing but Chal- 
cids. But to our surprise the 4. abrupta bees, even under 
such persecution, were more abundant the second year 
than the first. This is a good example of the delicate 
balance in nature’s game of cat and mouse. 
By June 28, 1918, as many chalcids were dead and 
strewn about the bank, in burrows and in crevices, a8 
were alive and on the wing; thus that date marked the 
decline of the first generation, which in the preceding 
year occurred on July 15. SomeAnthophora cells taken 
a little latter contained live pupae. So, comparing the 
dates of this species for 1917 and 1918, we see that when 
the first generation got a thirty days’ earlier start, 80 
likewise did the second generation. 
In 1920 this species appeared in about the same num- 
bers, and the interval dividing the two generations again 
came in July. To be exact, on my visit on July 21, not 
one Chaleid was to be scen. But on the next inspection, 
September 2, they were out again in great numbers. 
These of the second generation were, in turn, all gone 
