148 A BOOK OF INSECTS 



cases. The struggle for life among insect-eating animals 

 must lead some to acquire the power to feed upon kinds 

 which others cannot touch. And the fact that brilliantly 

 hued insects at times fall victims to hungry birds, lizards, 

 or monkeys, cannot destroy the experimental evidence 

 that bright colours are commonly associated with hurtful 

 or nasty qualities." 



Probably the strongest testimony to the value of 

 warning coloration in Nature is afforded by the like- 

 ness which many harmless insects bear to others that are 

 harmful or disagreeable. Such cases are usually referred 

 to as " mimicry," although the word is sometimes em- 

 ployed to describe deceptive appearances which should 

 really be spoken of as protective resemblance. This con- 

 fusion should be avoided. True mimicry, as interpreted 

 by science, consists in the external likeness of a poorly 

 protected animal (the mimic) to a well protected one (the 

 model), whereby the former is enabled to share in the 

 immunity from attack enjoyed by the latter. Thus, we 

 ought not to say that a butterfly mimics a leaf, or that 

 a stick is mimicked by a caterpillar. 



Let us examine an actual instance of mimicry among 

 British insects. The poplar clearwing moth (Trochilium 

 apiformis) is very unlike a typical moth. Its wings are 

 transparent, tinged with yellow ; its thorax is brown, with 

 a square patch of bright yellow on each side ; its abdomen 

 is yellow, with a brown belt near the base, and another 

 near the middle ; while its legs are deep orange. It has, 

 moreover, a general air of trim alertness that is very 

 unusual among scale-winged insects. But although the 

 poplar clearwing is unlike a moth, it is very much like 

 a hornet (Fespa crabro). Indeed, it is doubtful whether 

 a casual observer could distinguish between the two insects 

 merely by ocular examination. Yet we know that a 



