RELATION OF PHOTOTROPISM TO SWARMING IN THE BEE 179 



manifestation of photopositiveness is not confined to any given 

 period, such as the nuptial flight, has been amply confirmed in 

 my observations. I have already called attention to the fact 

 that among individual bees an active animal exhibits, almost 

 without exception, strong positive phototropism. Large aggre- 

 gates of bees also show marked positive light reactions quite 

 aside from swarm activities, as the following observations clearly 

 show. 



The glass observation hive with its single comb of bees was 

 situated at a south window where it was exposed to the sun 

 during the morning hours. With the oncoming of the cool days 

 of late October and early November, the bees became much less 

 active. On bright days, however, the exposure to the warmth 

 of the sun, and the corresponding rise of temperature within the 

 hive, served to activate the colony until most of the bees were 

 moving about the walls of the hive in a rapid uneasy manner. 

 If at such a time the cover was removed from the end nearer 

 the window, thus admitting the light, there was with the first 

 penetrating rays, a sudden increase of the hum within. There- 

 upon ensued a scene no less spectacular than that described by 

 Kellogg ('03, p. 693). His words picture it exactly, ". . . . 

 the whole community of excited bees flowed that is the word 

 for it, so perfectly aligned and so evenly moving were all the 

 individuals of the bee current ," toward the illuminated side. 

 A few hours later, however, when the sun had passed from the 

 hive and the temperature had fallen, particularly on the cooler 

 days, the uncovering of one end of the hive elicited no such 

 response. With perhaps the exception of a very few individuals, 

 the bees remained quietly in the swarm cluster. Nor was this 

 failure to obtain a response a result of the lowered intensity of 

 light, for the active worker bee responds to a fairly low intensity. 

 It must, therefore, have been due to the difference in temperature. 



These facts, together with those previously stated, demon- 

 strate conclusively that the pronounced phototropism, so con- 

 spicuous in swarming bees, is not confined to the period of 

 swarming. This condition of photosensitivity appears to remain 

 fairly constant at all times in the animal, although active locomo- 



