Bees, too, are sometimes so well imitated that they are hardly to be distinguished from their mimics, not in flight only, but also when visiting flowers. The best and commonest mimic of our honey-bee is a perfectly harmless fly of the same size and colour, the drone-fly (Eristalis tenax). The two are often to be seen together on the same flowering shrub, as, for instance, in autumn, on the Japanese buckwheat of our gardens (Polygonum sieboldii), both busily seeking for honey. I once noticed a boy catching the flies with a net in order to imprison them, but a bee stung him severely in the finger. He immediately abandoned the chase, and gave up the flies, perceiving the dangers of confusion. So the animal enemies of Eristalis will often prefer to leave it in peace rather than run the risk of being stung.

PLATE III

FIG.
24.Elymnias undularis, male of the species of which the
mimetic female is depicted in Fig. 23.
25.Euplœa binotata, immune Indian species, mimicked by
26.Elymnias leucocyma, male, of which
27.Euplœa midamus.
28.THE FEMALE MIMICS FAIRLY CLOSELY
29.Danais vulgaris, immune Indian Danaid.
30.Elymnias lais, mimetic of the foregoing species, but only
on the upper surface. The lower surface retains the
original protective colouring representing a decaying
leaf.
31.Tenaris bioculatus, from the Papua region.
32.Elymnias agondas, mimics the foregoing species from the
same locality.

To face Plate III

There is still another relation between two species which can be induced by mimicry—namely, parasitism, when, for instance, the so-called cuckoo-bees and parasitic humble-bees deceptively resemble in colour, arrangement of hair, and form of body, the species into whose nests they smuggle their eggs, to have them brought up at the expense of the bee or humble-bee in question. In the same way, among the numerous parasites of ant nests, there are some which copy the ants themselves, and so secure themselves from molestation, although they devour the ants' eggs and pupæ. Thus, among the hosts of South American driver-ants (Eciton prædator) there lives a predaceous beetle of the family Staphylinæ, which has received the name Mimeciton because it resembles the ant in form and in the nature of the external surface, though not in colour, which is to be explained by the fact that this ant has no compound eyes, and is therefore almost blind, or at any rate cannot see colours.

I should never come to an end were I to attempt to exhibit the great wealth of observations now available in regard to mimicry. But this at least may be added, that isolated cases of mimicry have been found even among Vertebrates. Thus, according to Wallace, the red-and-black striped poisonous coral snake of South America (Elaps) is most realistically imitated by a non-poisonous snake (Erythrolampus) of the same region. Among birds, Wallace cites a few cases which may be regarded as mimicry, but none are known among mammals, which is not to be wondered at when we consider how very much less numerous in individuals the species are which live together on one area, and how much less likely it is that two species should be, to begin with, so near each other in size, habit, and form that the process of natural selection could bring about a deceptive degree of resemblance. Without doubt it is among insects that the conditions for mimicry are especially favourable, partly because of the enormous number of species which live together and have interrelations on the same area, even in our latitudes and much more so in the tropics, and also because of their usually great fecundity, and their rapid multiplication, both of which are factors favourable to starting and continuing the processes of natural selection. Furthermore, we have to take into account the hosts of enemies which depend wholly or in great part on insects for food, and destroy them in enormous numbers, eliminating them in inverse proportion to the perfection of their adaptation. Finally, there is the extreme susceptibility of many insects to injury. This makes it very desirable that they should have some disguise sufficient to protect them from even the first attempt at an attack, since that would in many cases prove fatal.