 The English zoologist Edward Bagnall Poulton studied animal coloration , especially camouflage . In his 1890 book The Colours of Animals , he classified different types such as " special protective resemblance " ( where an animal looks like another object ) , or " general aggressive resemblance " ( where a predator blends in with the background , enabling it to approach prey ) . His experiments showed that swallowtailed moth pupae were camouflaged to match the backgrounds on which they were reared as larvae . Poulton 's " general protective resemblance " was at that time considered to be the main method of camouflage , as when Frank Evers Beddard wrote in 1892 that " tree @-@ frequenting animals are often green in colour . Among vertebrates numerous species of parrots , iguanas , tree @-@ frogs , and the green tree @-@ snake are examples " . Beddard did however briefly mention other methods , including the " alluring coloration " of the flower mantis and the possibility of a different mechanism in the orange tip butterfly . He wrote that " the scattered green spots upon the under surface of the wings might have been intended for a rough sketch of the small flowerets of the plant [ an umbellifer ] , so close is their mutual resemblance . " He also explained the coloration of sea fish such as the mackerel : " Among pelagic fish it is common to find the upper surface dark @-@ coloured and the lower surface white , so that the animal is inconspicuous when seen either from above or below . " 
