200 EN TOMOLOGY 
Pictet has recently found, however, that humidity acting 
on the caterpillars of Vanessa urtice and V. polychloros has 
a conspicuous effect on the coloration of the butterflies. Thus 
when the caterpillars were fed for ten days with moist leaves, 
the resulting butterflies had abnormal black markings on the 
wings, and the same results followed when the larve were 
kept in an atmosphere saturated with moisture. 
Climatal Coloration.—The brilliant and varied colors of 
tropical insects are popularly ascribed to intense heat, light 
and moisture; and the dull monotonous colors of arctic insects, 
similarly, to the surrounding climatal conditions. Climate 
undoubtedly exerts a strong influence upon coloration, but the 
precise nature of this influence is obscure and will remain so 
until more 1s known about the effects separately produced by 
each of the several factors that go to make up what is called 
climate. 
The prevalence of intense and varied colors among tropical 
insects is doubtless somewhat exaggerated, for the reason that 
the highly colored species naturally attract the eye to the ex- 
clusion of the less conspicuous forms. Indeed, Wallace 
assures us that, although tropical insects present some of the 
most gorgeous colors in the whole realm of nature, there are 
thousands of tropical species that are as dull colored as any 
of the temperate regions. Carabidz, in fact, attain their 
greatest brilliancy in the temperate zone, according to Wal- 
lace, though butterflies certainly show a larger proportion of 
vivid and varied colors in the tropics. Mayer finds, in the 
widely distributed genus Papilio, that 200 South American 
species display but 36 colors, while 22 North American species 
show 17. While the number of species in South America is 
nine times as great as in North America, the number of colors 
displayed is only a little more than twice as great; hence 
Mayer concludes that the richer display of colors in the tropics 
may be due to the far greater number of species, which gives 
a better opportunity for color sports to arise; and not to any 
direct influence of the climate. Furthermore, the number of 
