The Ecology of a Sheltered Clay Bank 221 
It will be seen that some of the creatures were of 
little or no importance in the balance of life on the clay 
bank; for instance the squash-bug, Anasa tristis, which 
is a vegetable feeder and which few creatures would 
eat, would have little influence on the life of the social 
group. On the other hand, some of the visitors wielded 
a significant influence, as in the case of Vespa germanica 
which carried off the Chalcid parasites which preyed 
upon the bees. Many of the visitors might be placed 
alternatively in still another group, those which might 
properly be considered as either renters or pioneers, 
as for instance, the spider-hunter, Pseudagenia archi- 
tecta, which might be said to carry on its daily busi- 
ness at the bank, although it maintained its home else- 
where. Of course the sharp line of demarcation between 
the groups is difficult to define while the possibility is 
always open for the visitors to become residents there 
and participate in all the joys and sorrows incidental 
to influencing the balance of nature already present, 
by preying, by being preyed upon or by parasitizing 
other creatures or by becoming hosts for other para- 
Sites, 
(e) Parasites. 
The following account presents the details of the 
activities of the last group of the inhabitants of the 
bank, the parasites, which affected the pioneers and the 
renters. These exerted their influence upon the balance 
of population in a variety of ways, and in turn were 1n- 
fluenced in interesting ways by some creatures from 
all three groups. 
