THE EUMENIDAE 325 



caterpillar properly between forelegs and mandibles, and 

 fly away with it. Was she a deliberate robber, or was she 

 only a home-seeker who had by error entered the wrong 

 nest and was removing only that which she had brought 

 with, her and which was rightfully hers? These wasps are 

 usually very careful in rinding their nests, and while they 

 sometimes peep into two or three others before arriving at 

 their own, we have seen only this one go so far as to enter 

 the hole of another. 



One day we saw a black wasp running and hopping about 

 in the region of the holes of O. dorsalis for about five min- 

 utes; finally it entered one of the holes, and we captured it, 

 as it emerged, to ascertain its identity. It was a Notogoni- 

 dea argentata Bve. [S. A. Rohwer]. In this case, too, we 

 were uncertain whether NotogonMea was invading the nest 

 of Odynerus through a blunder or through mal-intent. This 

 wasp hunts crickets, and she probably entered this hole in 

 search of them. 



Certain Diptera sometimes pester Odynerus. One two- 

 celled nest, which we found apparently securely sealed, 

 contained eight Diptera pupae. 



On the same day on which we made the above discovery, 

 September 18, we watched a small gray Dipteron, Hilarella 

 n. sp. [C. H. T. Townsend], following an O. dorsalis which 

 was homeward bound with her green caterpillar. The little 

 fly tagged behind her most persistently, keeping just at a 

 safe distance, a few inches to the rear of the wasp. It fol- 

 lowed and poised in the air with all the skill which insects 

 of their profession usually display. Both flew near to the 

 ground, and if O. dorsalis rested for an instant, the fly 

 would hover or poise on vibrating wings a few inches away; 

 if the rest was prolonged, the fly would rest on the ground 

 or a grass-blade nearby. It was pretty to see the shadow 

 on the whitened earth of the two insects in the bright sun- 



