1916] The Sleep of Insects 237 



from 2 to 60 males. Although it was past seven o'clock on an 

 August morning and the sun was high, all were still at rest. 



At 5 :30 in the afternoon, while it was yet full day, I examined 

 two large dormitories of Elis and found almost all of them in 

 their sleeping position already, although they were yet very 

 susceptible to even a sHght movement at some distance. One 

 of these groups occupied certain plants in the heart of a clump 

 of Erigeron. By 7:05 o'clock when I returned to the place they 

 were at rest on these plants in great numbers. Suddenly, 

 without apparent provocation, they all arose and flew about in 

 circles for several minutes before they again settled. Some 

 cause other than myself was responsible for the disturbance, for 

 I stood fifteen feet away. The behavior was the more strange 

 because they had become well settled in the hour and a half 

 since first I had found them there. Furthermore they settled 

 promptly to perfect quietude again, so that only a few minutes 

 later I removed a whole plant with one vigorous stroke of the 

 knife and carried it some distance without perceptibly dis- 

 turbing them. 



One month later, September 24, one lone male Elis was 

 found sleeping at 6 p. m. in the head of a white snakeroot. This 

 one, the belated straggler of the season, was the only one I ever 

 saw sleeping in solitude. It was the last seen that year; neither 

 have I been able to find them earlier in the season than June 16. 

 Thus it is clear that this gregarious sleeping institution is not 

 a thing merely of local origin but one deeply ingrained in the 

 species. Yet in spite of these observations on so many hundreds 

 of the wasps, we have no light upon the question of why the 

 males congregate thus and where and how the females sleep. 



Priononyx atratum Lept. [S. A. Rohwer]. 



One side of the road was lined with clumps of Erigeron 

 canadensis. These tall, slender plants were at this stage of 

 their growth about five feet tall. They seemed to be the dor- 

 mitory of the wasps of this species which worked in a near-by 

 corn-field. 



At 5:30 o'clock on the morning of August 13, I found six 

 wasps sleeping very close together at a point about three inches, 

 from the apex of one plant. The other stalks harbored no 

 insects at all although they grew very close together in this one 

 clump. I mention this to show that they could as easily have 



