May, 1910.] 
Nesting Habits of Bembex. 
i6 5 
A small species of fly, presumable a tachinid, was observed 
very active about the entrances to the burrows, and it was 
amusing to watch these little rascals, one or more of which were 
usually on hand whenever a burrow was being opened. The 
wasp seems very nervous when opening her nest, frequently 
pausing in her task to run hither and thither about the half- 
opened entrance or to rise on the wing and buzz around at vary- 
ing distances from it. But no matter what the circumstances 
were the little fly always faced the wasp, seeming to realize that 
its safety lay in its vigilance; and the rapidity with which it 
would face about or dart from side to side as the wasp moved 
about it, left little room to doubt that it was up to some sort of 
mischief. If the wasp moved away from the opening to any 
great distance the fly would dash into the burrow and in an 
instant pop out again at a lively pace; but in the instances 
observed the fly accomplished nothing by its bold dashes, for the 
wasp had not opened the burrow deep enough to permit the fly to 
reach the brood chamber. Frequently as the wasp entered her 
nest one, and sometimes several, of these flies would dash into 
the entrance behind her, only to have their eyes flung full of dirt 
bv the cautious wasp as she closed up the opening from within. 
Just what business these little rascals had in the burrow I 
failed to make out. Perhaps they sought to parasitize the larva 
of the wasp or perhaps to place their eggs upon the food provided 
for it. I found no evidence of parasitism but in two instances I 
found small larvae of some sort feeding on the flies in a chamber 
containing an immature larval wasp. That enemies are feared 
by the wasp seems evident from the fact that the entrance to the 
nest is never left open even when the wasp is inside it. 
One man complained of these wasps, insisting that they 
stung his horses when at work in the fields. But the presence of 
large numbers of stable-flies in the brood chambers shows that 
the wasp is a friend of the horse, not an enemy as my friend had 
supposed. The fact that they attack the houseftv is also much 
to their credit, but the presence of tachina-flies among the food 
of the larvae indicates that their habit of preying on flies is not 
wholly commendable. The extent of my investigation, however, 
was too limited to permit me to hazard an opinion as to their 
economic position. 
