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 
Pecilocapsus 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. 
