194 INSTINCT. [CHAP. VHL 



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 

 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 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 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 of 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 large birds to this cause; 



