CHAP. IV. | MEANS OF DEFENCE IN INSECTS. 39 



C, D, E, etc., belonging to the same group, share in the benefit con- 

 ferred by future immunity from attack by that individual bird. In 

 the case of such a " Mullerian " association, therefore, there is no 

 "' model," strictly speaking; all the associates are "models," but, 

 on an average, the commonest (/.<•., most numerous in individuals) 

 member of the group will pay the heaviest toll. In the case of 

 "Batesian " associations it is obvious that, for the mimicry to be 

 effective, (l) the model must outnumber the mimic in individuals, 

 and (2) both model and mimic must occur contemporaneously in the 

 same area ; if the mimic were not less numerous any enemies would 

 discover by experience (by the law of average) that insects of that 

 particular fades were palatable and such colours — which, we have 

 already stated, are ex hypothesi conspicuous — would invite attack 

 (ami, incidentally, speedy extermination of the insect attacked) 

 instead of avoidance, 



Insects which are distasteful are, we have just seen, often 

 brightly coloured, but not all the gaily-hued gems of a collection 

 of insects are necessarily distasteful. Many are indeed surprisingl) 

 inconspicuous when seen in their natural surroundings, with which 

 their colours blend in complete harmony, and others secure safety 

 from enemies by their wariness, activity, or speed on the wing. 

 Many butterflies, which exhibit most beautiful markings on the 

 upper surface of the wings, are sombrely coloured beneath and 

 extremely inconspicuous when at rest with their wings closed 

 together over the back. Numerous insects, in almost all the larger 

 Orders at least, combine a conspicuous type of marking when on 

 the wing with a very inconspicuous appearance when at rest, such 

 insects usually making short sudden flights on disturbance, and 

 the sudden apparent vanishing of its prey in this way must often 

 secure such insects from successful attack by an enemy. Really 

 nauseously distasteful insects, on the other hand, are often conspi- 

 cuous and slow-moving as if to advertise their security from attack ; 

 the term "warning colours " is therefore well applied to such 

 combinations of colour-markings. 



Some insects exhibit markings which tend to draw the attack 

 of an enemy to some non-vital portion, usually of the wings, the 

 insect itself thus escaping with slight damage. Amongst such 

 "directive" markings we may specify particularly the tails, eye- 

 spots, etc., on the hind-margin of the hindwings of many butter- 

 flies. In some of the Lyczenidas (e.g., Apliiurus and Virachola) the 

 inner corner of the hindwing is not only provided with tails and eye- 

 spots but is turned downwards at right angles to the rest of the wing 

 so that, in the resting position when the wings are appressed together 

 over the back, these little flaps of the wing simulate the anterior 



