20S INSTINCT. [Chap. VIII 



by the ant. Even the quite young aphides behaved in this manner, 

 showing that the action was instinctive, 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 anothei 

 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 abso- 

 lutely 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 dependence on the situations 

 chosen, and on the nature and temperature of the country inhabited, 

 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 deficient " ? 

 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 oi 

 laboriously collecting propolis, used a cement of wax and turpentine, 

 with which he had covered decorticated 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 particular 

 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 this even in 

 England, in the greater wildness of all our large birds in comparison 

 with our small birds ; for the large birds have been most persecuted 

 by man. We may safely attribute the greater wildness of our 

 larjre birds to this cause : for in uninhabited islands large birds are 



