158 C. H. TURNER. 



was readily seen that the piles of pellets were formed by the wasps 

 that were walking and depositing pellets. Careful observation 

 demonstrated that the piles of pellets were always associated with 

 those nests that were partly covered by the low weeds growing on 

 certain portions of plots c and c. What is the cause of this strik- 

 ing difference in the behavior of these wasps? Are some members 

 of the species born with an instinct for flying and scattering pellets 

 and other members of the same species born with an instinct for 

 walking and depositing pellets, or is there some relation between 

 the partial covering of nests by low-growing weeds and the change 

 from flying to walking? 



EXPERIMENTAL INVESTIGATION OF THE PLASTICITY OF THE 



CARRYING BEHAVIOR. 



If some members of this species are born with an inflexible 

 instinctive tendency to fly and scatter pellets and other members 

 of the same species are born with a fixed instinct to walk and 

 deposit them in piles, nothing in the way of an experiment can 

 alter matters; but if, in response to a certain environment, the 

 walking form of behavior has been derived from the flying, then 

 it should be possible to experimentally demonstrate it. Since the 

 low-growing weeds do not make flight impossible, if they are the 

 cause of the change in behavior it must be because they render fly- 

 ing with a load so unpleasant that the insect takes to walking to 

 avoid the unpleasantness. The problem that faced me was to 

 devise some apparatus that would permit the insect to fly, but 

 which, at the same time, would render flying with a burden so 

 unpleasant as to cause the wasp to abandon the attempt. 



In the experiments I used what might be called an interference 

 maze, constructed out of stove wire. The maze was constructed 

 in the field. A burrow was selected from which the wasp was 

 flying and scattering pellets. Several pieces of wire were stuck, 

 near together, in the ground near one of the nest openings. These 

 wires were then so bent as to radiate over the burrow like the 

 rays of a fan. Near the nest these wires were only an inch, or a 

 little less, above the surface of the ground. As they extended 

 outward they became gradually higher and higher until they 



