620 SCIENCE PROGRESS 



are active in the daytime being extremely small, though a 

 fairly large section, including the interesting hawkmoths, which 

 form the subject of another paper {Nineteenth Century, Feb. 

 1 921), are content to feed during the twilight of early morning 

 and evening. These night feeders are thus able to rest during 

 the daylight hours, and even if they remain exposed to view, 

 the absence of any movement on their part affords a consider- 

 able measure of concealment, which is very much increased 

 by approximation of form and colour to the surroundings. 

 Feeding, as the majority do, upon the leaves of plants, it is 

 only in accordance with what we should expect, that most 

 caterpillars are green in colour. Of those which are not of 

 this protective hue, many adopt a different and perhaps 

 superior method of concealment. These belong to the great 

 tribe Noduce, which comprises, for the most part, soberly 

 coloured moths, which fly only at night. 



Most of these caterpillars are of the same dirty white or 

 yellow colour familiar in the case of purely subterranean larvae, 

 except that it is usually very much darker in shade or is broken 

 up by dark bands or stripes, which are interesting as showing 

 just how larvae which are, as it were, breaking away from the 

 restrictions imposed by an underground existence may most 

 profitably vary to accord with new conditions. 



These Noctuid larva5 pass the daytime buried in the ground, 

 under stones, the loose bark of trees, or in the debris which 

 surrounds the base of established plants. They very rarely 

 remain on the leaves during the hours of sunshine, but shun 

 daylight and only creep forth when darkness has fallen. 



Small though it may be, there is, however, a certain amount 

 of risk run, even by night. There are a few enemies, bats, 

 frogs, mice, and predatory insects of other orders, which hunt 

 at night, and their senses are naturally adapted to the hours 

 of gloom, which, though called dark, are not by any means 

 entirely free from light. On a normal summer night a white 

 object is distinctly discernible, even by the ill-adapted human 

 eye, and it is manifest that the white colour of purely sub- 

 terranean larvae would be most unsuitable for night-rambling 

 in the open. Hence the general darkening in colour, or, what 

 is perhaps more significant, tendency to the non-actinic yellow 

 shades noticeable in this great group, while the frequent 

 appearance of stripes and bars is now well recognised as one 

 of the most perfect means of concealing the outline of an 

 object. As everyone knows, it was employed during the great 

 war to disguise shipping, and proved very effective. 



One may therefore dismiss, as of no specialised interest, 

 the species of moth-larvae which live underground, feeding on 

 the roots of plants or venturing out only in the night-time ; 



