The Tracking Instinct in a Toriugas A7it. 105 



around the fly. Then, when the ant leaves the fly and proceeds 

 more or less in the direction of the nest, it soon meets with the barrier 

 of corrosive sublimate. This arrests it. It then crawls around 

 close to the inner edge of the barrier, then suddenly goes straight 

 back to the dead fly, and again starts out for the nest, to be again 

 arrested by the barrier of corrosive sublimate. Finally, after re- 

 peating these m.ovements a number of times, it crosses the barrier 

 and goes in a more or less direct path toward the nest; but when it 

 meets other ants and rubs antennae with them they are not excited 

 and no swarm comes back to the dead fly. The fact that the ''finder 

 ant" has crossed the corrosive sublimate seems to have destroyed 

 its power to excite other ants or to draw them back to the lure it 

 has found. 



II. Conversely, if after a ''finder ant" has gone back to the nest, 

 and the swarm is well established and the fly is being torn to pieces, 

 a circle of corrosive sublimate be drawn around the fly, the ants 

 coming from the nest are at once arrested when they reach the 

 outside of the ring of poison. A block occurs and in about a minute 

 nearly every ant between the outside of the ring and the nest is 

 seen to be returning straight to the nest, so that the swarm vanishes 

 in a short time. The ants caught within the ring usually show some 

 hesitation in crossing the poisoned area, and once having crossed, 

 they rarely return to the fly, so that the numbers attacking the 

 fly constantly decrease, due to lack of new recruits. 



III. On one occasion an ant which was carrying a grain of sand 

 in its mandibles found a dead fly and "inspected" it in the usual 

 fashion, but did not drop the grain of sand. It then crawled ofi" 

 toward the nest, carrying the sand, but no return swarm came. 

 No inferences can be drawn from this observation, however, for it 

 is based on only a single case, although it seems possible that under 

 certain conditions a "finder ant" does not produce a return swarm. 



IV. If after having found the fly the "finder ant" is allowed to 

 go toward the nest and to rub antennae with several of its nest- 

 mates, and is then gently brushed up from the floor with a camel's- 

 hair brush and removed, the ants it has encountered show normal 

 excitement; and this excitement spreads by contact to others in 

 their neighborhood, but no return swarm occurs. The excited ants 

 rushing to and fro often cross the path the "finder ant" traversed in 

 going from the fly toward the nest, but none of them attempts to 

 follow the trail back to the fly. 



V. If the "finder ant," after having "inspected" the fly and 

 started toward the nest, is brushed up and carried through the air 

 to the nest-crevice, the ants it falls among may at times display 

 some excitement, but of this I am uncertain. Certainly, however, 

 no return swarm comes back to the fly. Apparently, having been 



