56 ON PLANTS AND INSECTS. [LECT. 



brown. The green ones are obviously merely those 

 which have retained their original color. Now for 

 the brown color. This probably makes the caterpillar 

 even more conspicuous among the green leaves than 

 would otherwise be the case. Let us see, then, 

 whether the habits of the insect will throw any 

 light upon the riddle. Wha.t would you do if you 

 were a big caterpillar ? Why, like most other de- 

 fenceless creatures, you would fepd by night, and lie 

 concealed by day. So do these caterpillars. When 

 the morning light comes, they creep down the stem 

 of the food plant, and lie concealed among the thick 

 herbage, and dry sticks and leaves, near the ground, 

 and it is obvious that under such circumstances the 

 brown color really becomes a protection. It might 

 indeed be argued that the caterpillars, having become 

 brown, concealed themselves on the ground ; and that we 

 were in fact reversing the state of things. But this 

 is not so; because, while we may say, as a general 

 rule, that (with some exceptions due to obvious causes) 

 large caterpillars feed by night and lie concealed by 

 day, it is by no means always the case that they are 

 brown ; some of them still retaining the green color. 

 We may then conclude that the habit of concealing 

 themselves by day came first, and that the brown 

 color is a later adaptation. It is, moreover, interest- 

 ing to note, that while the caterpillars which live on 

 low plants often go down to the ground, and turn 

 brown, those which feed on large trees or plants 

 remain on the under side of the leaves, and retain 

 their green color. 



Thus, in Smerinthus ocellatus, which feeds on the 



