More Beetles 



race would be the better for the change and 

 would become more numerous, since there 

 would be plenty of food in perfectly safe 

 places. 



If the Geotrupes does nothing of the kind, 

 if it has never even attempted to do so, apart 

 from my artificial methods of rearing, it is 

 because the regimen is not determined merely 

 by the appetites of the consumers. Eco- 

 nomic laws regulate the diet and each species 

 has its portion, in order that nothing shall be 

 left unused in the treasury of unorganizable 

 matter. 



Let us consider a few examples. The 

 Death's-head Hawk-moth (Acherontia atro- 

 pos, LINN.) has the leaves of the potato for 

 her caterpillar's portion. She is a foreigner, 

 who seems to have come from America to- 

 gether with her food-plant I have tried to 

 rear her caterpillar on various plants belong- 

 ing, like the potato, to the family of the 

 Solanaceae. Henbane, datura and tobacco 

 were obstinately refused, despite the acute 

 hunger displayed when the normal food was 

 served. 



The violent alkaloids with which these 

 plants are saturated may perhaps explain this 

 refusal. We will therefore keep the true 

 224 



