CHAPTER III 



THE INFLUENCE OF EXTERNAL CONDITIONS IN CAUSING 

 CHANGES IN THE STRUCTURE OF ANIMALS {Continued) 



Experiments on the Influence oj the Food Plant 



PiCTET has studied the influence of the food of the caterpillar 

 on the color, the size, and other characters of the butterfly. 

 As a rule the caterpillars of each species are found on a par- 

 ticular plant, and cannot be induced to eat the leaves of a differ- 

 ent one, or only with great difficulty. A few species, however, 

 are polyphagous, i.e. they feed on a number of different plants. 

 For example, the caterpillars of the Arctiidae feed upon aU sorts 

 of herbaceous plants; many Noctuidae consume indifl"erently 

 several species of Compositae ; Papilio macchaon Hves on dif- 

 ferent UmbelHferae ; Ocneria dispar, Porthesia chrysorrhaea, and 

 Bombyx neustria are found on nearly all kinds of trees. ^ Occa- 

 sionally caterpillars are found on plants that are not those nor- 

 mal for them, and the question has often been asked whether 

 the aberrant types of butterflies sometimes met with may not 

 have arisen in consequence of a change in the food plant. This 

 question Pictet has studied experimentally. 



In captivity certain caterpillars adapt themselves readily to 

 very different kinds of food. As a rule a caterpillar will feed 

 on the flowers of its natural plant, and even the fruit may be 

 used, as in the case of Cossus cossus, which will eat pieces of 

 apple instead of the wood and the bark of the tree. 



It appears that in nature, also, certain species have recently 

 extended their dietary. Thus Lasiocampa quercus was known 

 at the time of Linnaeus to feed on the oak tree (as its 



^ These examples are given by Pictet. 

 29 



