Fitness in the Living World 3 * 7 



rous plants catch insects by sticky secretions or traps, and 

 they then infold and digest them. The plant known as 

 "Venus fly-trap" does not respond, by closing, to a single 

 stimulus, such as would be produced by accidental contact 

 with a falling object, but only when the stimulus is repeated 

 within three minutes, as it would be if that object were an 

 insect; incidentally, this behavior shows that this plant has 

 a kind of memory ("organic memory") which lasts for a 

 period of about three minutes. 



The behavior of higher plants and animals is almost 

 always adaptive, and where it is not so it can usually be 

 explained as the result of unnatural, or at least unusual, 

 conditions; thus the tendency of insects to fly into a flame is 

 the result of positive phototropism, which is beneficial in 

 a state of nature and injurious only in the artificial condi- 

 tions created by man. The behavior of insects is sometimes 

 so remarkably adaptive that it seems to be intelligent and 

 purposive. Thus the solitary wasp, Sphex, digs a burrow in 

 the ground and stores it with caterpillars which have been 

 stung in such a way as to paralyze but not to kill them. On 

 these caterpillars she lays her eggs, and when the larvae 

 hatch they find an abundance of fresh meat for food. On 

 leaving the burrow the mother Sphex carefully conceals it 

 by closing it with earth; the Peckhams and more recently 

 several others have observed that she then takes a small 

 stone in her mandibles and pounds the earth down with it 

 and then smooths the earth so that all traces of the burrow 

 are removed. The instincts of ants and bees have long been 

 studied, but they never lose their charm and interest; the 

 instincts of the different castes or members of the colony, 

 and even of the same individual at different stages of its 

 life, are very unlike, and yet all are adapted to the preserva- 

 tion and prosperity of the colony. 



