SEXUAL SELECTION 425 



tremely tender, and as their intestines readily protrude from 

 a wound, a slight peck from the beak of a bird would be as 

 fatal to them as if they had been devoured. Hence, as Mr. 

 Wallace remarks, "distastefulness alone would be insuffi- 

 cient to protect a caterpillar, unless some outward sign 

 indicated to its would-be destroyer that its prey was a 

 disgusting morsel." Under these" circumstances it would 

 be highly advantageous to a caterpillar to be instantane- 

 ously and certainly recognized as unpalatable by all birds 

 and other animals. Thus the most gaudy colors would be 

 serviceable, and might have been gained by variation and 

 the survival of the most easily recognized individuals. 



This hypothesis appears at first sight very bold, but when 

 it was brought before the Entomological Society" it was sup- 

 ported by various statements; and Mr. J. Jenner Weir, who 

 keeps a large number of birds in an aviary, informs me that 

 he has made many trials, and finds no exception to the rule, 

 that all caterpillars of nocturnal and retiring habits with 

 smooth skins, all of a green color, and all which imitate 

 twigs, are greedily devoured by his birds. The hairy and 

 spinose kinds are invariably rejected, as were four conspicu- 

 ously colored species. When the birds rejected a caterpillar, 

 they plainly showed, by shaking their heads and cleansing 

 their beaks, that they were disgusted by the taste. " Three 

 conspicuous kinds of caterpillars and moths were also given 

 to some lizards and frogs, by Mr. A. Butler, and were re- 

 jected, though other kinds were eagerly eaten. Thus the 

 probability of Mr. Wallace's view is confirmed, namely, that 

 certain caterpillars have been made conspicuous for their 

 own good, so as to be easily recognized by their enemies, 

 on nearly the same principle that poisons are sold in colored 



83 "Proc. Entomolog. Soc," Dec. 3, 1866, p. xlr., and March 4, 1867, 

 p. Izzx. 



^ See Mr. J. Jenner Weir's paper on Insects and Insectivorous Birds, in 

 "Transact. Ent. Soc," 1869, p. 21; also Mr. Butler's paper, ibid., p. 27. Mr. 

 Eiley has given analogous facts in the "Third Annual Report on the Noxious 

 Insects of Missouri," 1871, p. 148. Some opposed cases are, however, giveu 

 by Dr. Wallace and M. H. d'OrviUe; see "Zoological Record," 1869, p. 349. 



