COLORATION OF LAND SNAILS. 187 



PROTECTIVE DEVICES AND COLORATION OF LAND 



SNAILS. 



By HENRY A. PILSBRY, 



CONSERVATOR, DEPARTMENT OF MOLLUSCA, ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA. 



THIRTY years ago, when Bates wrote his modest observations 

 upon the protective mimicry of the butterflies of the Ama- 

 zons, few naturalists could have foreseen the vital and far-reach- 

 ing influence those now classic pages would have upon the future 

 of biology. But the new doctrine, taken up by Darwin, Wallace, 

 and others, and illustrated by hundreds of examples among in- 

 sects, birds, and mammals, has already taken its place among the 

 established canons of zoology. 



The general principles of the subject of mimicry are now fa- 

 miliar to the laity as well as to scientists ; but much still remains 

 for observation at our very doors, to supplement the known facts, 

 and to extend the underlying principles of mimicry and protective 

 resemblance to the less-known groups of animals, among which 

 are the land mollusks. 



We have been made familiar with many cases of what may be 

 called true mimicry, occurring among the insects ; such as the 

 conspicuous resemblance some moths, which are of course both 

 defenseless and edible, bear to wasps and other stinging insects ; 

 and the instances of edible butterflies mimicking in their colors 

 nauseous species are also well known. A more striking case of 

 this phase of mimicry has quite recently been noticed in tropical 

 America. In the forests of this region, leaf-cutting ants live in 

 countless numbers. They strip whole trees of their foliage, 

 carrying the leaves in fragments to their formicaries. Now, 

 among these ants have been found insects belonging to an entirely 

 different order, which mimicked the ant and its leafy burden ! 

 The back of the mimicking insect is green, and pinched up into a 

 flat, thin plate, quite the counterpart of the leaf -fragment carried 

 by the ant.* 



A much more simple case is represented by the dead-leaf 

 butterfly of Java, which, when it alights upon a bush, presents 

 so close a resemblance to a dead leaf that even so experienced a 

 naturalist as Wallace was long deceived by it. This resemblance 

 of an animal to its surroundings may be called " protective re- 

 semblance," rather than mimicry. 



Instances such as these might be multiplied indefinitely, were 

 we to confine ourselves to the insect world. The great variety of 



* See the article by Edward D. Poulton on this insect, Proceedings of the Zoological 

 Society of London, 1861. 



