BEHAVIOR OF A PARASITIC BEE 389 



of their behavior subsequent to mating. When alighting from 

 flight such a bee would almost invariably alight on the netting 

 of that side of the cage through which the direct rays of the 

 sun were entering; but, in her flight, she would frequently 

 cross the rays of light in every possible direction (Ex. 23). In 

 roaming about on foot, the bee would cross the rays of light in 

 every possible direction (Ex. 21). Frequently the bee would 

 remain exposed to the direct rays of the sun without making 

 any outward response (Ex. 22). Under the same external con- 

 ditions, the same bee, at successive moments, did not always 

 make the same response to the impinging light (Ex. 20, 23). 

 Occasionally a bee would fly about the cage, crossing the rays 

 of light at every possible angle, and hover before each side 

 of the cage as though examining it (Ex. 17). These striking 

 variations from a fixed response militate against calling this 

 behavior a tropism in the restricted sense mentioned above. 



It seems more in harmony with the facts to assume that light, 

 heat, hunger, sexual restlessness and, perhaps, other factors 

 arouse in these bees an impulse to roam from home, and that, 

 coupled with this impulse to roam, there is an instinctive ten- 

 dency to seek freedom in the direction of the incoming rays 

 of light. When following this instinctive tendency fails to 

 bring freedom, the bee tries other methods. In this endeavor, 

 many bees make haphazard flights in all possible directions, 

 usually concluding by yielding to the instinctive impulse to 

 move in the direction of the rays of light and towards their 

 source ; while yet other individuals, in a more systematic manner, 

 rejJeatedly hover before each side of the enclosure as though 

 looking for an opening. When, in their ramblings, they find 

 something which it is to their interest to revisit they make 

 a flight of orientation which furnishes them with memory 

 pictures that assist them in revisiting the place. At twilight 

 these bees are stimulated to seek the mud cells that serve as 

 home. When we state that these parasitic bees are endowed 

 with a pronounced tendency to move in the direction of the 

 rays of light and towards their source; but that they do not 

 invariably so react, for they frequently display unpredictable 

 variations, we have given as strong a mechanical interpretation 

 as the facts warrant. If it is desirable to call this kind of a 

 response a tropism then these bees are positively phototactic. 



