COLOR AND COLORATION 215 



two colors in many butterflies and beetles are due to pigments 

 that are closely related to each other chemically. Thus in the 

 chrysomelid Melasoma lapponica the beetle at emergence is 

 pale but soon becomes yellow with black markings, and after 

 several hours, under the influence of sunlight, the yellow 

 changes to red ; the change may be prevented, however, by keep- 

 ing the beetle in the dark. After death, the red fades back 

 through orange to yellow, especially as the result of exposure 

 to sunlight. Yellow in place of red, then, may be attributed 

 to an arrested development of pigment in the living insect and 

 to a process of reduction in the dead insect, metabolism having 

 ceased. 



Yellow and green are similarly related. The stripes of 

 Pcecilocapsus lineatus are yellow before they become green, and 

 after death fade back to yellow. As the green pigment in most, 

 if not all, phytophagous insects is chlorophyll, these color 

 changes are probably similar to those that occur in leaves. 

 Leaves grown in darkness are yellow, from the presence of etio- 

 lin, and do not turn green until they are exposed to sunlight (or 

 electric light), without which chlorophyll does not develop; 

 and as metabolism ceases, chlorophyll disintegrates, as in 

 autumn, leaving its yellow constituent, xanthophyll, which is 

 very likely the same substance as etiolin. 



Cicindela sexguttata and Calosoma scrutator are often blue 

 in place of green. Here, however, these colors are structural, 

 and their variations are to be attributed to slight differences in 

 the spacing of the surface elevations or depressions. 



Green grasshoppers occasionally become pink toward the 

 close of summer. No explanation has been offered for this 

 phenomenon, though it may be remarked that when grasshop- 

 pers are killed in hot water the normal green pigment turns to 

 pink. 



These changes of color are apparently of no use to the insect, 

 being merely incidental effects of light, temperature or other 

 inorganic influences. 



