76 ANIMAL AGGREGATIONS 



their mandibles. Bradley also records finding Melissodes agilis cling- 

 ing on dried blades of wild oats alongside a newly cut grain field. In 

 this same patch were large aggregations of a number of species of 

 wasps — no two species on the same blade. He accounts for the aggre- 

 gations of wasps as being caused by the cutting of nearby grain. 

 Boyer and Buchsbaum of this laboratory, from their unpublished 

 observations, think that the Melissodes which Bradley found ag- 

 gregated were present because of the cutting of the flowers on which 

 they ordinarily collect. 



Von Frisch (1918) gives observations on 6 solitary male bees, 

 Halictus, which returned for 4 days to the same dry stem of a plant. 

 He records that the bees would return to this plant if the weather 

 grew bad or if the temperature became low, even during daylight. 

 For 4 evenings after his original observation he observed 5 bees pres- 

 ent on the same stem, although there were other similar stems near- 

 by. One bee had been taken for identification. He cannot be sure 

 that the same five returned each evening. 



The Raus have several notes on bees. Concerning Melissodes ob- 

 ligua they s,a.y: ". . . . We found the twenty-eight bees clustered near 

 the tops of a small clump of stalks. Since it was now almost dark my 

 presence did not disturb them. They were huddled together in 

 groups of two to five, with only three insects occupying their sites 

 singly. 



"The next evening twenty-nine bees, only one more, were asleep 

 on these five stems, all clustered on the apical three inches of the 

 dead plants. At the top of another plant ten feet away, two were at 

 rest. If they had chosen this site for protection alone they would 

 have rested singly on the plants, but since they huddled in groups 

 they must have sought sociability also. They were so close together 

 in some cases as to arouse suspicion about their mating, but a close 

 examination proved the idea false. 



''The following night, July 21, twenty-four of these bees were here 

 to spend the night in the same way. On the 22nd, thirty were pres- 

 ent. On this evening I marked part of them with white paint 



As fate would have it, the next evening a cow had broken down their 

 chosen stems, so none of the bees were there. However, fifteen were 

 found on similar weeds nearby; seven of these bore the white mark- 



