386 JOHN H. GEEOULD 



the food plant and produces a definite change at every stage in 

 the fife-history, including the color of the newly laid egg, of the 

 blood and body wall of the caterpillar and pupa, and of the blood 

 and eyes of the adult. 



The caterpillar of C. philodice feeds upon clover, and is of a 

 yellow-green hue corresponding so closely to that of the plant 

 as to be remarkably inconspicuous. Larvae that are feeding in 

 full view of the observer are almost invisible unless in motion or 

 seen in profile. Although the butterfly is common and I have 

 raised thousands of the caterpillars, I have not found in the open 

 field in the twelve seasons that I have worked upon this species 

 as many, probably, as twelve caterpillars. Imagine, then, my 

 surprise when in August, 1920, caterpillars that were conspicu- 

 ously blue made their appearance in two of my cultures upon 

 potted clover plants in the greenhouse and my further astonish- 

 ment when a similar state of affairs was soon afterwards dis- 

 covered in an outdoor culture upon a series of clover plants 

 covered with cages. 



Self-colored blue, or more accurately blue-green, caterpillars 

 are almost unknown in Lepidoptera. Only two species among 

 diurnal butterflies have as yet come to my notice, both European 

 pierids, Anthocharis cardamines and Pieris ergane. None of 

 the species closely related to either, so far as I know, are blue- 

 green, so that it is possible that each has experienced in its 

 ancestral lineage a mutation like the one here described for 

 Colias philodice, also a pierid. Toyama ('12) mentions the 

 occurrence of blue silkworms, "a Mendelian characteristic and 

 recessive to the normal-skinned characteristic," due, as he states, 

 to the absence of pigment in the hypodermis. 



The color sensation that the mutant caterpillars give one 

 against the food plant as a background is like that produced by 

 blueberries on a bush, and it was only by comparing them side 

 by side with blueberries (Vaccinium) that I first convinced myself 

 that they are slightly more green than blue. 'Light porcelain 

 green' of Ridgeway's ('12) Color Standards (pi. 33, B-G), classed 

 as 'blue-green,' corresponds closely to the ground color of the 

 full-grown caterpillar. 



