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THE POPULAR SCIENCE MONTHLY.— SUPPLEMENT. 



tion applied to many other groups of animals. 

 Thus bees and wasps and other stinging insects 

 are showily and distinctively colored ; many soft 

 and apparently defenseless beetles, and many 

 gay-colored moths, were found to be as nau- 

 seous as the above-named butterflies ; other 

 beetles, whose hard and glossy coats-of-mail 

 render them unpalatable to insect-eating birds, 

 are also sometimes showily colored; and the same 

 rule was found to apply to caterpillars, all the 

 brown and green (or protectively-colored species) 

 being greedily eaten by birds, while showy kinds 

 which never hide themselves — like those of the 

 magpie-, mullein-, and burnet-moths — were utterly 

 refused by insectivorous birds, lizards, frogs, and 

 spiders (" Contributions to Theory of .Natural 

 Selection,'' page 117). Some few analogous ex- 

 amples are found among vertebrate animals. I 

 will only mention here a very interesting case not 

 given in my former work. In his delightful book 

 entitled " The Naturalist in Nicaragua," Mr. Belt 

 tells us that there is in that country a frog which 

 is very abundant, which hops about in the day- 

 time, which never hides himself, and which is 

 gorgeously colored with red and blue. Now, frogs 

 are usually green, brown, or earth-colored, feed 

 mostly at night, and are all eaten by snakes and 

 birds. Having full faith in the theory of protec- 

 tive and warning colors, to which he had himself 

 contributed some valuable facts and observa- 

 tions, Mr. Belt felt convinced that this frog must 

 be uneatable. He therefore took one home, and 

 threw it to his ducks and fowls ; but all refused 

 to touch it except one young duck, which took 

 the frog in its mouth, but dropped it directly, and 

 went about jerking its head as if trying to get 

 rid of something nasty. Here the uneatableness 

 of the frog was predicted from its colors and 

 habits, and we can have no more convincing 

 proof of the truth of the theory than such pre- 

 visions. 



The universal avoidance by carnivorous ani- 

 mals of all these specially protected groups, which 

 are thus entirely free from the constant persecu- 

 tion suffered by other creatures not so protected, 

 would evidently render it advantageous fcr any 

 of these latter which were subjected to extreme 

 persecution to be mistaken for the former, and 

 for this purpose it would be necessary that they 

 should have the same colors, form, and habits. 

 Strange to say, wherever there is an extensive 

 group of directly protected forms (division a of 

 animals with warning colors), there are sure to 

 be found a few otherwise defenseless creatures 

 which resemble them externally so as to be mis- 



taken for them, and which thus gain protection 

 as it were on false pretenses (division b of ani- 

 mals with warning colors). This is what is called 

 "mimicry," and it has already been very fully 

 treated of by Mr. Bates (its discoverer), by my- 

 self, by Mr. Trimen, and others. Here it is only 

 necessary to state that the uneatable Danaida; 

 and Acraeidse are accompanied by a few species 

 of other groups of butterflies (Leptalida3, Papi- 

 lios, Diademas, and Moths) which are all really 

 eatable, but which escape attack by their close 

 resemblance to some species of the uneatable 

 groups found in the same locality. In like man- 

 ner there are a few eatable beetles which exactly 

 resemble species of uneatable groups ; and others, 

 which are soft, imitate those which are uneatable 

 through their hardness. For the same reason 

 wasps are imitated by moths, and ants by bee- 

 tles ; and even poisonous snakes are mimicked 

 by harmless snakes, and dangerous hawks by de- 

 fenseless cuckoos. How these curious imitations 

 have been brought about, and the laws which 

 govern them, have been discussed in the work 

 already referred to. 



The third class — sexual colors — comprise all 

 cases in which the colors of the two sexes differ. 

 This difference is very general, and varies greatly 

 in amount, from a slight divergence of tint up to 

 a radical change of coloration. Differences of 

 this kind are found among all classes of animals 

 in which the sexes are separated, but they are 

 much more frequent in some groups than in 

 others. In mammalia, reptiles, and fishes, they 

 are comparatively rare and not great in amount, 

 whereas among birds they are very frequent and 

 very largely developed. So among insects, they 

 are abundant in butterflies, while they are com- 

 paratively uncommon in beetles, wasps, and he- 

 miptera. 



The phenomena of sexual variations of color, 

 as well as of color generally, are wonderfully 

 similar in the two analogous yet totally unrelated 

 groups of birds and butterflies; and, as they both 

 offer ample materials, we shall confine our study 

 of the subject chiefly to them. The most com- 

 mon case of difference of color between the sexes 

 is for the male to have the same general hue as 

 the females, but deeper and more intensified ; as 

 in many thrushes, finches, and hawks; and among 

 butterflies in the majority of our British species. 

 In cases where the male is smaller the intensifi- 

 cation of color is especially well pronounced, as 

 in many of the hawks and falcons, and in most 

 butterflies and moths in which the coloration 

 does not materially differ. In another extensive 



