192 A BOOK OF INSECTS 



pillar upon the leaves of the monk's-hood — the most deadly 

 of all the buttercup tribe; while the poison ivy (Rhus 

 toxicodendron) is eaten by the caterpillars of at least three 

 moths and the larva of a beetle. 



Insects differ widely in their choice of vegetable food, 

 and display preferences which are often unaccountable. 

 Thus, a species may feed exclusively upon one plant, or at 

 most upon a few closely related kinds. The caterpillars 

 of the famous large copper butterfly ( Chrysophanus dispar) 

 appear to have fed only upon the leaves of the great 

 water-dock, and this fact, in conjunction with the drain- 

 ing of the fen districts, goes far to explain the insect's total 

 extinction, which was accomplished about the year 1860. 

 The caterpillars of the large fritillary butterflies feed upon 

 violet leaves throughout the wide range of the group in 

 the temperate regions of the northern hemisphere, while 

 those of the sulphur or brimstone butterflies are equally 

 dependent upon buckthorn. On the other hand, certain 

 insects will eat almost any kind of vegetation to which 

 they have access. The caterpillars of the gipsy moth 

 (Psilura dispar) have been observed, in a wild state, to 

 feed indifferently upon seventy-eight species of plants. In 

 captivity they ate 458 species, thirty under stress of 

 hunger, the rest freely. Only nineteen species of those 

 offered were refused, and most of these possessed highly 

 poisonous or pungent juices, or were too tough to be 

 bitten. Again, the migratory locusts are notoriously 

 destructive ; now, as of old, their invading armies " eat 

 every herb of the land, and all the fruit of the trees." 



While many insects browse openly among the foliage, 

 others burrow between the upper and lower cuticles of 

 leaves, and subsist upon the soft inner tissue, or par- 

 enchyma. Some of these leaf-miners form long, winding 

 tunnels, the graceful curves of which are not displeasing 



