272 KANSAS UNIVERSITY SCIENCE BULLETIN. 



by females. I believe that males wait for females at the en- 

 trance of burrows when the latter are about to emerge. At 

 any rate, one was brought to me by Mr. Mallory which he had 

 taken waiting at the entrance of a burrow in which was a 

 female almost ready to come out. 



Both males and females of this species were frequent in 

 lowland fields and pastures, but I seldom saw one on a hillside. 

 In some places they were common on lamb's-quarter and croton 

 plants. The former was the food plant of one of its caterpillar 

 prey. The latter also may have been frequented for the same 

 reason, but quite often I saw this wasp on the croton flower, 

 apparently seeking nectar. 



O. arvensis does not have the colonial nesting habit, nor does 

 it favor one nesting site to the exclusion of all others, as does 

 0. papago7-um. Consequently its nests were less easily found 

 and its habits not so readily studied. 



0. arvensis, as I found her, was always a burrowing was].. 

 Her burrows were the least carefully made of the digging 

 Eumenidse that came under my observation. The variation 

 that may occur in the nesting habits of a single species of wasp 

 is here shown. This same species, when observed by Mr. Hart- 

 man in Texas, made her domicile in any convenient crevice ir. 

 a wall or fence post. 



An open space near water seemed to be the only char- 

 acteristic common to all the nesting sites I observed. During 

 the summer I noted eighteen nests in the course of construc- 

 tion or finished. Of these six were located in the talus at the 

 base of cliffs along the edge of streams, two in moist flats 

 within a few feet of the water's edge, five were in cow paths 

 in pastures, three in open spaces in pastures, one in an open 

 space in fallow land, and one other in the dry bed of an inter- 

 mittent stream. One of these burrows opened in a short 

 growth of grass, while the others were in spaces practically 

 free from grass or weeds. One was located in a cow path 

 running through a narrow strip of timber, while all the others 

 were in sunny places. All the nests were within thirty yards 

 of water but one, which was about a hundred yards from water. 

 The character of the soil in which the nest was located seemed 

 to be a matter of no consequence. There was every gradation 

 from a hard clay mixed with limestone — so hard that I could 

 scarcely dig into it with my knife — to the soft alluvial soil of 

 the flats beside the streams. 



