See [page 30]
One who collects the Underwing moths soon discovers that the light colored species which resemble the bark of birch trees are likely to be found upon the trunks of those trees, and that the dark colored kinds which resemble the bark of maple trees are likely to be found upon the trunks of these. Obviously, were this not true the protective coloring would avail but little and it is evident that these moths are able to select a background which is of advantage in helping to conceal them.
There is much evidence to show that in a similar way the butterflies are able by means of a well-developed color sense to select the places where they alight. One of the most notable examples is that of a South American species, Peridromia feronia. This is a silvery gray butterfly which alights head downward upon the bark of certain palm trees that have silvery gray stems and remains there with its wings fully expanded so that it utilizes the background in much the same way that the Underwing moths do. "When disturbed they will return to the same tree again and again."
One who will observe the habits of our Angle-wings and other butterflies which have obliterative coloring of the under wing surface can easily learn that these insects select rather carefully the places where they alight. It will be found that as a rule each species utilizes a background that blends with its own coloring. It is probable that this habit is much more common in other groups of butterflies than has been realized. Much evidence of this sort has been collected regarding the butterflies of Europe and other countries, as well as near our own borders in America.
Warning Coloration and Mimicry
The colors of a great many animals, including a considerable percentage of American butterflies and their larvae, have been commonly explained by the theory of warning colors. According to this theory animals which were for any reason not edible by birds and mammals have developed various striking combinations of color such as black and yellow, red and black, or black and white, in order to advertise to their foes their inedible qualities. This theory has been very generally accepted by naturalists and will be found expounded at length in many books published during the last quarter century.
The whole subject of the validity of warning coloration has recently been brought up for reconsideration by the illuminating investigations of Mr. Abbott H. Thayer and discussed at length in the book upon "Concealing Coloration" already mentioned. In an appendix to this book dated 1908 Mr. Thayer states that he no longer holds the belief that "there must somewhere be warning colors." He has convincingly shown that a large proportion of the animals which were supposed to be examples of this theory are really illustrations of concealing coloration. But there yet remain various facts which have been conclusively proven that apparently require the theory of warning colors to explain them. Here is another field in which there is a real need for much careful investigation under conditions that are rigidly scientific.