A WEEK WITH A MINING EUMENID. 163 



HOMING EXPERIMENTS. 



While observing these wasps excavate their nests I was deeply 

 impressed by two things : the facility with which the wasp, on re- 

 turning with water, located her nest in the midst of surroundings 

 which, to my senses, were almost uniform, and how easily she 

 could be confused by slight changes in the environment. Almost 

 any disfigurement of the surface of the ground would cause her to 

 have trouble in locating her nest. Small pieces of tile and nails 

 used to mark certain nests and radiating lines which I scratched 

 about others caused confusion. In each case the reaction was the 

 same. Arriving in the vicinity of the nest, the wasp would circle 

 about in an irregular manner, sometimes afoot and sometimes 

 awing, as though lost. After a certain length of time it would 

 either find the nest or else abandon the attempt and start another. 

 If the nest were found, before taking another trip afield, the wasp 

 would always make a careful flight of orientation. 



In the following words Isely ('14, p. 294) states how easily the 

 wasps he studied were affected by changes in the surface of the 

 ground: "Although not generally sensitive to observation, 0. dor- 

 sails was more responsive to changes in the surroundings of her 

 burrows than was O. papagonim. A few marks with a knife, to 

 assist in locating a nest at a later time, seemed to disturb one wasp 

 considerably. On her return to the nest she made a prolonged 

 flight of irregular circles above her nest, while she was in the habit 

 of alighting without any hesitation. On another occasion I muti- 

 lated slightly the entrance to a burrow. Upon the wasp's return 

 she circled around the burrow a few times and then alighted about 

 two inches from the entrance. She flew away and returned in 

 about a minute and repeated the observation performance. Again 

 she flew away and returned without entering. This time she ap- 

 parently deserted her nest." 



Evidently, when in the neighborhood of the nest. Odyncnts dor- 

 sails finds her way by means of landmarks. How keen, then, must 

 be her powers of observation since she sees landmarks in a situation 

 where we see only uniformity! 



