408 Evolution and Adaptation 



nest, they separate quietly ; if of other nests, they may fight. 

 If an ant from one nest is put into another nest, it is instantly 

 attacked and killed — an act that appears to be injurious 

 rather than useful, for the ant might become a valuable mem- 

 ber of the new colony. If, however, an ant is first immersed 

 in the blood of a member of the community into which she 

 is to be introduced, she will not be attacked, and may soon 

 become a part of the new community. By her baptism of 

 blood she has no doubt acquired temporarily the odor of the 

 new nest, and by the time that this has worn off she will 

 have acquired this odor by association, and become thereby a 

 member of another colony. 



Numerous stories have been related of cases in which an 

 ant, having found food, returns to the nest with as much of 

 it as she can carry, and when she comes out again brings with 

 her a number of other ants. This has been interpreted to 

 mean that in some mysterious way the ant communicates her 

 discovery to her fellow-ants. A simpler explanation is proba- 

 bly more correct. The odor of the food, or of the trail, 

 serves as a stimulus to other ants, that follow to the place 

 where the first ant goes for a new supply of the food. The 

 fact that the first individual returns to the supply of food 

 seems to indicate that the ant has memory, and this is obvi- 

 ously of advantage to her and to the whole colony. 



The peculiar habits of some of the solitary wasps, of sting- 

 ing the caterpillar or other insect which they store up as 

 food for their young, is often quoted as a wonderful case 

 of adaptive instinct. The poison that is injected into the 

 wound paralyzes the caterpillar, but as a rule does not kill it, 

 so that it remains motionless, but in a fresh state to serve 

 as food for the young that hatch from the egg of the wasp. 

 A careful study of this instinct by Mr. and Mrs. Peckham 

 has shown convincingly that the act is not carried out with the 

 precision formerly supposed. It had been claimed that the 

 sting is thrust into the caterpillar on the lower side, a ventral 



