3io WASP STUDIES AFIELD 



This burrow was dug out at about 5 p. m. ; perhaps the 

 little owner had merely gone into her burrow for a night's 

 lodging, or it may be that we had only caught her there 

 when busy with nidification. While we suspect that 0. 

 geminus sleeps in her hole the same as does O. dor sails, we 

 found one insect asleep on Melilotus, clinging to the stalk. 

 However the sex of this individual was not noted. 



The very first O. geminus worker of the year was seen 

 in the field on June 5, but they were not at all common 

 until August, and most of the above notes were made in 

 the first half of September. Some which we reared at 

 home emerged as adults in June. On September 24, we 

 noted that during that week the turrets of geminus had 

 been scarce. This disappearance of wasps was probably 

 due to the increasing coolness and the fact that their nor- 

 mal season was over; but it may also have been due to the 

 fact that all the puddles of water in the vicinity had dried 

 up in the long-continued drought. 



Of the hundreds of caterpillars exhumed from the nests 

 of 0. geminus, every one was of the same species. They 

 were identified by Dr. S. B. Fracker as belonging to the 

 genus Loxostege, of the family Pyraustidae. Dr. Fracker 

 writes further that it was difficult to be sure of the species 

 since the alcohol had taken out all the color, but in all 

 probability they were L. similalis. Thus the two species of 

 Odynerus, O\. geminus and 0. dorsalis, dwelt together in 

 this field (fig. 2) and found plentiful food for their young, 

 yet each adhered strictly to her own choice of prey, the 

 one using only Loxo siege and the other taking exclusively 

 Pholisora catullus. Since the two species are so similar, it 

 seems to us surprising that they should be so strict in their 

 choice of prey as never to accept what is entirely pleasing 

 to the other. Hungerford and Williams 2 note a similar 



2 Ent. News 23 : 254. 



