IN DEFENSIVE COLORATION 319 



element as a protection against the special enemies 

 which attack the species in spite of their unpalatability. 

 The more completely the larva is concealed from 

 special enemies, and the more visible it is to enemies 

 which respect the defence of unpalatability, the greater its 

 chance of survival. The compromise is effected in these 

 species by concealment at a distance, passing into con- 

 spicuousness on a near approach, combined with further 

 defensive methods when an actual attack is made. 



Abrupt changes in the method of protection in the 

 course of the life-history are very common. Thus the 

 caterpillar of Cucullia verbasci produces a moth possess- 

 ing a beautiful Cryptic colouring, the resemblance being 

 to a splinter of wood. Euchelia jacobaeae, on the other 

 hand, becomes even more Aposematic in the perfect than 

 in the larval state. One of the most beautiful instances 

 of change is afforded by the larva of the rare British 

 species Acronycta alni. In its young stage the cater- 

 pillar bears the closest likeness to the excrement of 

 a bird : at a change of skin it suddenly emerges with 

 a startling black and yellow pattern which has all the 

 appearance of a Warning character. 



Even more interesting are the species which by some 

 significant movement pass at once from the Cryptic to 

 the Aposematic category. The change thus undergone 

 by certain larvae was described in 1887 * by the 

 present writer : — ' Such larvae are apt to pass unnoticed 

 because of the harmony between their colours and mark- 

 ings and the artistic effect of their surroundings ; but, if 

 discovered, or even if an enemy approach so that there is 

 danger of their being discovered, the protective [cryptic] 

 attitude is instantly changed for one which renders the 

 larva conspicuous, and warns the enemy of the presence 

 of unpleasant attributes (taste or smell), or alarms it by 

 the resemblance of the new appearance to some object of 

 terror [the reference is here to C. elpenor as described on 

 PP« 367 > 368]. These facts may even be true of gregarious 

 larvae. Thus a group of phytophagous Hymenopterous 



1 Proc. Zool. Soc, Lond., 1887, pp. 197, 204. See also pp. 206, 207 

 of the same memoir, where experiments on four species are recorded. 



