164 ENTOMOLOGY 



are simply a direct effect of cold upon the wintering chrysalides. Simi- 

 larly the spring brood (variety marcia) of Phyciodes tharos owes its dis- 

 tinctive coloration to cold, as Edwards has proved experimentally. 

 Lepidoptera have been the subject of very many temperature experi- 

 ments, some of which will be mentioned presently in the consideration of 

 seasonal coloration. 



Speaking generally, warmth (except in melanism] tends to induce a 

 brightening and cold a darkening of coloration, the darkening being due 

 to an increased amount of black or brown pigment. Temperature, 

 whether high or low, seldom if ever produces new pigments, but simply 

 alters the amount and distribution of pigments that are present already. 



Effects of Moisture. Very little is known as to the effects of mois- 

 ture upon coloration. The dark colors of insular or coastal insects as 

 contrasted with inland forms, and the predominance of dull or suffused 

 species in mountainous regions of high humidity, have led observers oc- 

 casionally to ascribe melanism and suffusion to humidity. In these cases, 

 however, the possible influence of low temperature and other factors must 

 be taken into consideration. The experiments of Merrifield and of 

 Standfuss showed no effect of moisture upon lepidopterous pupae. 



Pictet has found, however, that humidity acting on the cater- 

 pillars of Vanessa urticce 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 

 larvae 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 re- 

 main so until more is 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 exclusion 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 tem- 

 perate regions. Carabidae, in fact, attain their greatest brilliancy in the 

 temperate zone, according to Wallace, though butterflies certainly show 



