1 62 ENTOMOLOGY 



ditions being equal, and are able at will to effect certain color changes 

 simply by feeding the larvae from birth upon particular kinds of plants. 

 In this country we have few observations upon the subject, but in Europe 

 the effects of food upon coloration have been ascertained in the case of 

 many species of Lepidoptera. According to Gregson, Hybernia defoliaria 

 is richly colored when fed upon birch, but is dull colored and almost un- 

 marked when fed on elm. Pictet, by feeding larvae of Vanessa urticce, on 

 the flowers instead of the leaves of the nettle obtained the variety known 

 as urticoides. Food affects the color of the larva also, as Poulton found 

 in the case of caterpillars of Tryphcena pronuba, all from the same batch 

 of eggs. When fed with only the white midribs of cabbage leaves, the 

 larvae remained almost white for a time, but afterward showed a moderate 

 amount of black pigment ; when fed with the yellow etiolated heart-leaves 

 or the dark green external leaves, however, the larvae all became bright 

 green or brown the same pigment being derived indifferently from etio- 

 lin (probably the same substance as xanthophyll) or chlorophyll. 



Though the pigments may differ in color or amount according to the 

 kind of food, the color patterns vary without regard to food. Thus 

 Callosamia promethea, Leptinotarsa decemlineata (Colorado potato beetle), 

 Coccinellidae (lady-bird beetles) and a host of other insects exhibit ex- 

 tensive individual variations in coloration under precisely the same food 

 conditions. Caterpillars of the same kind and age are often very dif- 

 ferently marked when feeding upon the same plant; for example, Helio- 

 this obsoleta (corn worm) and the sphingid Deilephila lineata. Further- 

 more, striking changes of coloration accompany each moult in most cater- 

 pillars, but particularly those of butterflies, and these changes may prove 

 to have an important phylogenetic significance. Individual differences 

 of coloration apart from those due to the direct action of food, light, 

 temperature and other environmental conditions are to be explained by 

 heredity. 



Effects of Light and Darkness. Sunlight is an important factor in 

 the development of most animalpigments, as they will not develop in its 

 absence. The collembolan Anurida maritima is white at hatching, but 

 soon becomes indigo blue, unless shielded from sunlight, in which event 

 it remains white until exposed to the sunlight, when it assume the blue 

 color. Subterranean or wood-boring larvae are commonly white or yel- 

 low, but never highly colored. The most notable instances, however, 

 are furnished by cave insects. These, like other cavernicolous animals, 

 are characteristically white or pale from the absence of pigment, if they 

 live in regions of continual darkness, but have more or less pigmentation 



