1916] The Sleep of Insects 229 



On July 2, at 7:45 a. m., a number of these blue wasps were 

 found assembled on the ceiling of an open cow-shed. The wasps 

 here had collected in two groups about four inches apart, and 

 a few individuals dotted the intervening space; during the next 

 few minutes they flew away one by one to their day's business 

 after having spent the night there. I watched the spot during 

 the day but none of them returned; at dusk however, they 

 began to arrive, and lo and behold! they settled on the same 

 spot and collected in two groups similar to those of the morning. 



I waited until almost dark, and when they were fast asleep 

 I removed about half of them with the forceps to ascertain if 

 both sexes commingled. The twenty insects which I took 

 were 9 males and 11 females. In attempting to take these 

 wasps earlier in the evening when they were not fully asleep, I 

 found them to be more than usually nervous and ever ready to 

 fly away. Sometimes when an attempt was made to take one, 

 simultaneously as if by magic all flew away, but when they were 

 asleep the task was easy; sometimes one grasp with the forceps 

 brought down three insects. Close observation showed that 

 none were in copulo. 



I resumed these observations when I again came to the 

 farm six weeks later. I then found a much larger congregation 

 on the same ceiling and the identical spot;. they were probably 

 the ones I had left and many newcomers. There were a hundred 

 or more crowded into an area of less than one square foot, and 

 again I noticed that while it was yet slightly light my gentlest 

 approach would invariably start them to flight simultaneously 

 as if by signal, and I sometimes even wondered if they had not 

 a sentinel on watch. When these wasps are engrossed in build- 

 ing or provisioning their nests one can observe them quite 

 closely without arousing such a reaction. On this particular 

 evening they were disturbed three times and each time they left 

 simultaneously, but invariably they returned one at a time. 



Careful examinations at various times have convinced me 

 that mating does not occur during these meetings, although 

 both sexes are always present, usually in equal numbers. I 

 have never been able to detect any evidence of their mating in 

 the evening or morning, and during the hours of darkness they 

 are in such deep sleep that they are dead to all the world about 

 them. Possibly they meet here preparatory to the marriage 

 flight when the sun is high. 



