56 Adaptive Mimicry. 



of red, yellow or white on a black or blue ground, — being also un- 

 protected by any less gorgeous colouring of the underwing, — 

 being also very large and slow lazy flyers, would be such an 

 obvious and easy source of supph' to the many lavenous birds 

 which feed on butterflies, that the}^ might in their defencelessness 

 be extirpated in a single summer, but for the fact that they exude 

 an intensely pungent yellow liquid, so disgusting, that not even 

 the most ravenous puflf-bird or lizard, which has the smallest sense 

 of self-respect, will deign to touch them. Now among these 

 Heliconidae which are thus defended, may be found a large num- 

 ber of another genus, the Septalides, wholly different from them in 

 characterising marks, yet bearing to them so close an external 

 resemblance, that they easily escape annoyance by passing off as 

 belonging to them. The curious point is that the butterflies which 

 thus live in masquerade are almost solely females. And why is 

 this? Because the preservation of the female is essential to the 

 perpetuity of the race. The males are very short lived ; and if 

 they are killed a little sooner or a little later no great harm is 

 done ; but the life of the females must be preserved for a longer 

 time, and they are thus protected until they have laid their eggs 

 and the existence of the next generation is secured. It is probably 

 the same fact that causes the comparative duluess in the plumage 

 of female birds as compared with the male. The. male being 

 stronger, larger, and swifter of wing can better defend himself, 

 and moreover is not obliged to spend long hours in motionless 

 incubation. Not so the female, who must sit on her eggs for days 

 together, exposed to every open and secret foe, and who is there- 

 fore generally enabled to escape detection by the dusky incon- 

 spicuous lines which hide her as she sits in the hedges and tree 

 boughs. But you will object that in some cases the law is reversed, 

 especiall}' among some aquatic birds where the male is much less 

 bright in plumage then the female. This is true, and is a fresh 

 confirmation of the interesting fact on which we have been dwelling; 

 for it is found in all these cases that there is some special and 

 obvious reason for the disturbance of the apparant law, and in fact 

 in the majority of them the reason is this — that the male performs 

 the duties of incubation, while the female is busied in procuring 

 food. This is the case with the Dotterell and the sooty Phalarope, 

 and further, when incubation is performed in a dark hole, or dome- 

 shaped hanging nest, and when, therefore, the female has no 

 special need of protection during the dangerous period of hatching; 

 she is often (as in the case of the kingfisher and woodpecker) as 

 bright as the male. Among butterflies also, the Heliconidae, 

 protected in the manner we have just described, have the females 

 as bright as the males. 



