THE NEW EVOLUTION 



lochia (or pipe-vine) swallowtails which feed only on 

 Aristolochias and on very closely allied plants, and 

 also our fritillaries which feed almost exclusively 

 on violets. Very many kinds of butterflies feed only 

 on a single kind of plant, like our beaked butterfly 

 and tawny emperor which as caterpillars are found 

 only on hackberry trees. But a few kinds of butter- 

 flies, like our common yellow swallowtail, feed on a 

 very great variety of different and unrelated plants. 



From this it becomes evident that female butterflies 

 must be expert botanists, for they must be able accu- 

 rately to identify those plants which are suitable for 

 use as food by the caterpillars of the coming genera- 

 tion. Or perhaps it should be said that they must be 

 expert chemists, for not infrequently they will pick 

 out a plant chemically suitable as food, but botani- 

 cally widely different from any other plant which 

 they or their ancestors, at least for thousands of gener- 

 ations, could be supposed to know. 



As an illustration, the female of the common cab- 

 bage butterfly will freely lay her eggs on garden nas- 

 turtiums (Tropaolurn) which belong to a family of 

 plants (Tropasolacea^) confined to Central and South 

 America and not at all like any of the plants of the 

 cabbage family (Brassicaceas) upon which ordinarily 

 this Old World insect feeds. 



Butterflies have very many enemies of every con- 

 ceivable description. The Australian natives are very 

 fond of certain kinds of butterflies, and grow fat on 

 them if they can get them in sufficient quantities. 

 In Central and South America and especially in Africa 



