The Ecology of a Sheltered Clay Bank 225 
the first of October. The dates of these two generations 
were practically the same as in the first year; the first 
generation ran from late June to mid-July, and the see- 
ond appeared about the first of September but disap- 
peared before the end of the month, 
The animal most abundant in an ecological unit 
should be regarded as the dominant one. If this rule 
includes parasites, then we must admit that this Chaleid 
is the most abundant and dominant insect in the unit. 
They were already plentiful at the time of my first ob- 
servation; their hosts were well established and numer- 
ous, and since each host is capable of bringing to matur- 
ity, on an average, thirty or so parasites, we see how fa- 
vorable were all their prospects. And yet we come face 
to face with the fact that other parasites, Diptera, etc., 
even though they appear in far smaller numbers, di 
fully as much destruction to the permanent residents of 
the bank as did these many little Chalcids. What does 
it matter to an Anthophora larva, whether it yields its 
life to produce thirty-nine chalcids or one cuckoo-bee? 
Thus, we see that the most important aspect of the 
life of the Chalcids is to keep the bees from overrunning 
everything by their enormous increase in population, 
which would doubtless take place without this deterring 
influence. As a secondary function they serve as food 
for some species that in no other wise influence the life 
of the bank, such as non-resident Vespa germanica, and 
also to feed spiders which, by being thus encouraged 
to come to or stay on the bank, might also prey upon the 
other residents. 
