SOCIAL CATERPILLARS 133 



being social throughout their life they are more 

 than usually destructive to foliage, stripping branch 

 after branch, and wandering to the very tips until 

 these are borne down by the weight of the mass. 

 It would seem probable that our Eugonia has the 

 same habits from what we know of its European 

 congener, but if so it is exceedingly strange that 

 in only one instance has the caterpillar been seen 

 in this country, and then but a single one, proba- 

 bly one which was hastening to seek a place in 

 which to pupate. 



Although it is not stated whether the caterpillar 

 concerned belongs to a butterfly or to a moth, a 

 very curious and interesting case of strict commen- 

 salism has been noted by Fritz Miiller in South 

 America, in which a large spiny caterpillar was 

 almost invariably found accompanied by a small 

 hairy caterpillar, so small as to rest securely in a 

 transverse position across the back of its good- 

 natured host, well concealed among its spines ; in 

 proof of its continued existence at this point the 

 skin of the host was hardened beneath the tread of 

 its little guest, so as to have become distinctly 

 more callous than in other parts. Just what ad- 

 vantage this would be to either party, both be- 



