The Origin of the Markings of Caterpillars. 299 



glossa Steilatarum, Sphinx Convolvuli, and Ache- 

 rontia Atropos. 



The habit in question must therefore be the 

 result of certain external conditions of life common 

 to all those species which rest by day. The mode 

 of life common to them all is that they do not live 

 on trees with large leaves or with thick foliage, 

 but on low plants or small-leaved shrubs, such as 

 the Sea Buckthorn. 8 I believe I do not err when 

 I attribute the habit possessed by the adult larvae, 

 of concealing themselves by day, to the fact that 

 the green colour is protective only so long as they 

 are small or, more precisely speaking, as long as 

 their size does not considerably exceed that of a 

 leaf or twig of their food-plant. When they 

 become considerably larger, they must become 

 conspicuous in spite of their adaptive colour, so 

 that it would then be advantageous for them to 

 conceal themselves by day, and to feed only by 

 night. This habit they have acquired, and still 

 observe, even when the secondary adaptation to 

 the colour of the soil, &c., has not been brought 

 about. We learn this from D. Hippophaes, which 



8 [Eng. ed. The habit of hiding by day occurs also in those 

 caterpillars which resemble the bark of their food-trees. Thus 

 Catocala Sponsa and Promissa conceal themselves by day in 

 crevices of the bark, and are, under these circumstances, only 

 found with difficulty. Dr. Fritz Miiller also writes to me that 

 in Brazil the caterpillars of Papilio Evander rest in this manner 

 in large numbers, crowded together into dense masses, on the 

 trunks of the orange-trees, which they resemble in colour.] 



