78 ANIMAL AGGREGATIONS 



while 24 returns were noted to some flower more than 10 feet away 

 from the original. 



In 1928, 14 bees were successfully painted. Of these only 4 were 

 seen again; and of these, two returned to the same flower where they 

 were painted and the other two returned to a nearby flower. A study 

 of the details of the observations shows that males of Melissodes 

 frequently return to the same flower night after night or in cool or 

 cloudy weather. They are generally found in the same vicinity on 

 successive nights, even if not on the same flower. They must neces- 

 sarily return to a different flower if the one on which they have been 

 staying is destroyed or dries up. No bees were observed on withered 

 flowers. If they are blown to a distant part of the sunflower patch, 

 they tend to remain there in a narrowly circumscribed area for the 

 next several days. 



It must be noted that these overnight aggregations in Melissodes 

 were composed of males only.' They cannot have sexual significance. 

 It seems entirely possible that we are concerned here with an in- 

 cipient social habit which does not extend to many solitary species 

 and is not found in all individuals of the species in which it occurs. 



Swarming locusts of several different species are known to pass the 

 night in dense masses both as nymphs and later when they become 

 adults. Much of this literature is reviewed by Uvarov (1928). Re- 

 garding the overnight aggregations of these locusts, Uvarov says: 

 "The night is passed on plants in dense bands, which are extremely 

 conspicuous on the background of the vegetation owing to their 

 blackish general color ; during the night the hoppers are in a state of 

 torpor caused by the cold." If the day is cool, the slumber bands do 

 not break up as they do on warm sunshiny days. Even when con- 

 siderable numbers of the South African locust, Locustana pardalina, 

 have become adult, they collect at night near the main nymph 

 swarm, although they may range at considerable distance during the 

 day. The night clusters of the flying adults are not so dense as those 

 of the hoppers. 



Faure (1923), in describing the night collecting of nymphs, says 

 they gather slowly together into fairly dense masses, forming clusters 



' J. F. W. Pearson has taken 3 female Melissodes and 90 males from early morn- 

 ing collecting on Helianthus in this locality. 



