584 Color and Pattern and their Uses 



Some colors are obviously there simply because of the chemical make-up 

 of parts of the insect body. That gold is yellow, cinnabar red, and certain 

 copper ores green or blue are facts which lead us to no special inquiry after 

 significance; at least significance based on utility. And if an insect has 

 part of its body composed of or containing a substance that is by its very 

 chemical and physical constitution always red or blue or green, we may 

 be content with knowing it and not be too insistent in our demand to the 

 insect to show cause, on a basis of utility, for being partly red or blue or 

 green. And even if this red or blue be disposed with some symmetry, some 

 regularity of repetition, either segmen tally or bilaterally, this we may well 

 attribute to the natural segmental and bilaterally symmetrical repetition of 

 similar body parts. Some color and some color-pattern, then, may be 

 explicable on the same basis as the color of a mineral specimen or of a tier 

 of bricks. 



But no such explanation will for a moment satisfy us as to the presence 

 and arrangement of colors in the wing of Kallima, the dead-leaf butterfly 

 (PI. XIII, Fig. i), or in Phyllium, the green-leaf Phasmid (PL XIII, Fig. 2). 

 We demand an explanation based on direct and large usefulness to the insect. 



Certain uses seem pretty apparent: the brown and blackish pigments 

 in the compound eyes have the function of absorbing light-rays so that these 

 rays may be prevented from passing through the walls of adjacent ommatidia, 

 and thus confusing the mosaic vision; the pigment of the simple eye-flecks 

 of some insect larvae serves, as in the eye-spots of other simple animals, to 

 absorb light at a certain spot especially sensitive and thus make possible 

 a recognition of light intensity, a low grade, not of seeing, but of simple appre- 

 ciation of the presence or absence of light. Some color in the skin of insects 

 may serve, too, as is pretty certainly the case with many vertebrates, to 

 absorb heat or prevent its radiation, or, on the other hand, to reflect it, or 

 to allow it to radiate freely. In view of the cold-bloodedness of insects this 

 must be a use, in this class of animals, extremely restricted and infrequent. 

 But such uses as these are at best explanatory of but little of the wealth of 

 color and pattern manifest in the insect class. A utility more important, 

 and common to many more individuals and capable of explaining a specializa- 

 tion of color and pattern much more complex, is needed as a basis for color 

 significance. 



The green katydid singing in the tree-top or shrubbery is readily known 

 to be there by its music, but just which bit of green that we see is katydid 

 and which is leaf is a matter to be decided by unusually discriminating eyes. 

 The clacking locust, beating its black wings in the air, is conspicuous enough, 

 but after it has alighted on the ground it is invisible, or, rather, visible but 

 indistinguishable; its gray and brown mottled color-pattern is simply con- 

 tinuous with that of the soil. The green larvae of the Pierid butterflies 



