340 Trans. Acad, Scr. of St. Louts 
‘After the excavating is once done, the workers seem 
to have no objection to leaving the mouth of the burrow 
open. They are frequently to be seen on sunny days, 
with the face just within the aperture of the hole, their 
bright eyes shining as they gaze into the outer world. 
But if one comes too near, they, like C. raui, creep down, 
cautiously, almost imperceptibly; one does not realize 
that they are moving until they have vanished from 
sight. 
While Cerceris bicornuta persistently chooses for her 
nesting site a hard-packed soil, yet a number of times I 
have found evidence that she gladly avails herself of 
assistance in her digging by utilizing some hole already 
begun. In one case, one extended a neat hole left by a 
peg which had been driven into the ground and pulled 
out. In other instances they used and lengthened the old 
holes from which Bembiz nubilipennis had emerged (fig. 
36). While they do not seem actually to follow up the 
Bembix or depend upon them for their assistance, they 
frequently have the opportunity of availing themselves 
of it, since their choice of the same environment often 
brings them together. 
When one finds insects established in a city lot, one 
is inclined to think of them as relies from a preciviliza- 
tion period, clinging to their former habitat despite the 
tightening about them of urban conditions; one is sur- 
prised to learn that species new to the neighborhood are 
coming in and becoming established under our very eyes- 
Intensive Hymenoptera collecting in this vicinity for 
eleven years had not revealed one specimen of this wasP- 
The small area where they are now established was dur- 
ing the four years, 1913 to 1916, subjected to my very 
intensive study; observations were made almost every¥ 
day as I crossed the field, yet I never found a single speci- 
