May, 1910.] Nesting Habits of Bembex. 165 



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 para.sitism 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 housefly 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. 



