INSTINCT 211 



with its antennae on the abdomen first of one aphis and then of 

 another; and each, as soon as it felt the antennae, immediately 

 lifted up its abdomen and excreted a limpid drop of sweet juice, 

 which was eagerly devoured by the ant. Even the quite young 

 aphides behaved in this manner, showing that the action was in- 

 stinctive, and not the result of experience. It is certain, from the 

 observations of Huber, that the aphides show no dislike to the 

 ants: if the latter be not present they are at last compelled to 

 eject their excretion. But as the excretion is extremely viscid, it 

 is no doubt a convenience to the aphides to have it removed; 

 therefore probably they do not excrete solely for the good of the 

 ants. Although there is no evidence that any animal performs an 

 action for the exclusive good of another species, yet each tries to 

 take advantage of the instincts of others as each takes advantage 

 of the weaker bodily structure of other species. So again certain 

 instincts cannot be considered as absolutely perfect ; but as details 

 on this and other such points are not indispensable, they may be 

 here passed over. 



As some degree of variation in instincts under a state of nature, 

 and the inheritance of such variations, are indispensable for the 

 action of natural selection, as many instances as possible ought 

 to be given; but want of space prevents me. I can only assert that 

 instincts certainly do vary — for instance, the migratory instinct, 

 both in extent and direction, and in its total loss. So it is with the 

 nests of birds, which vary partly in independence on the situations 

 chosen, and on the nature and temperature of the country inhab- 

 ited, but often from causes wholly unknown to us. Audubon has 

 given several remarkable cases of differences in the nests of the 

 same species in the northern and southern United States. Why, 

 it has been asked, if instinct be variable, has it not granted to the 

 bee "the ability to use some other material when wax was de- 

 ficient?" But what other natural material could bees use? They 

 will work, as I have seen, with wax hardened with vermilion or 

 softened with lard. Andrew Knight observed that his bees, instead 

 of laboriously collecting propolis, used a cement of wax and tur- 

 pentine, with which he had covered decorated trees. It has lately 

 been shown that bees, instead of searching for pollen, will gladly 

 use a very different substance, namely, oatmeal. Fear of any par- 

 ticular enemy is certainly an instinctive quality, as may be seen in 

 nestling birds; though it is strengthened by experience, and by 

 the sight of fear of the same enemy in other animals. The fear of 

 man is slowly acquired, as I have elsewhere shown, by the various 

 animals which inhabit desert islands; and we see an instance of 



