Field Studies of the Non-Social Wasps 349 
A second P. mellipes was watched for fifteen minutes 
as she nervously walked on the walls or flew from place 
to place within the narrow confines of the shack. She 
was seen to enter a dozen empty cells of mud wasps, 
and one in particular claimed her attention. An hour’s 
wait, however, revealed no further activity on the part 
of this prospector. 
A third individual was seen to return often to a new 
and partly wet cell of S. caementarium which was in 
course of construction, and I am sure would have started 
something had not the owner, returning with her mouth- 
ful of mud, routed her with such hearty vigor that P. 
mellipes was discreet and never returned. ‘A fourth P. 
mellipes on an exploring expedition likewise entered 
several old nests but did not remain in any of them. 
They generally seem hard to please or for some unex- 
Plained reason they do a large amount of prospecting 
before they finally select a mud hut to remodel, although 
from my standpoint the offerings of available second- 
hand domiciles are all about equally good or bad. 
A fifth P. mellipes had a sixth one close at its heels 
as they both entered through a crack in the wall. The 
first one entered an unsealed cell and the other one 
still followed; after a few seconds, a wrangling was 
heard within and soon after they appeared fighting at 
the orifice, the victor threw the rival out, and as she 
fell toward the ground she expanded her wings and flew 
out at the door. The other remained within. Before 
I left an hour later, I inserted a blade of grass in the 
cell to ascertain if she was still present, whereupon she 
fled in alarm. Late that afternoon I had opportunity 
to return, and found her not in, but I did notice that 
the opening of the old cell had in the meantime been 
enlarged, and the jaw-marks gave evidence that some 
