THE CHOICE OF FOOD BY ANIMALS 89 



some barn or behind the shutters of a village school. 

 The winter of 1895-6 was so preternaturally mild 

 that there was nothing very surprising that, even 

 in the rigorous climate of Caithness, the small 

 tortoiseshell should have hybernated successfully. 

 Still, it was worth noting that, when I was start- 

 ing from the inn at Halkirk to fish on January 31, 

 feeling something tickling the back of my neck, I 

 put up my hand and caught a tortoiseshell butter- 

 fly. But the foregoing winter of 1894-5 was not 

 of a temper to spare many of these sleepers; the 

 marvel is how even the chrysalides, suspended head 

 downwards from the tail-tip, can have resisted a 

 temperature of several degrees below zero. One 

 would say that in order to preserve unfrozen the 

 circulatory fluid of the pupa, the rind of the chry- 

 salis must possess an extraordinary degree of non- 

 conductivity. 



XXXIII 



The small tortoiseshell is one of many handsome 



insects of which the larvae feed on the The choice 



of food by 

 stinging nettle. Some of the most ans- animals 



tocratic caterpillars make this plant their staple 

 diet the red admiral, for example, the lordly pea- 



