THE TRIBE OF THE ANGLE-WINGS 183 



spots near the front margin of each front wing and having 

 scattered iridescent scales which show plainly under a lens. 

 The suggestion of the coloring of a tortoise-shell is easily 

 seen in these rich brown tones. The under surface is a 

 wonderful illustration of protective coloring. With wings 

 closed and resting against the bark of trees or lying be- 

 neath the trees among fallen leaves, it would require a 

 keen eye to detect the insect. {See plates, pages 160-161,) 

 The American Tortoise-shell is distinctly a northern 

 species. North of latitude forty-three degrees it seems to 

 occur practically from ocean to ocean, extending far up to- 

 ward the arctic region. It is commonly found in British 

 America as far north as Fort Simpson in latitude sixty-one 

 degrees. There are specimens in the British Museum 

 collected by the explorer Ross in arctic America, and there 

 are many in our own National Museum collected in the 

 Hudson Bay region by various American explorers. In 

 New England the species is abundant at times in New 

 Hampshire, Vermont, and Maine. In the vicinity of New 

 York City and Buffalo, New York, it is rather rare. And 

 south of this latitude it is found chiefly at the higher ele- 

 vations in mountainous districts. As a rule it is likely to 

 vary in numbers from year to year, sometimes being ex- 

 tremely abundant while more commonly it is rather rare. 

 These are the same sorts of fluctuations that we find in the 

 case of the Mourning-cloak, the American tent cater- 

 pillar, and various other insects whose larvae live in col- 

 onies. The variation is probably due to the fact that 

 when the caterpillars become unusually abundant they be- 

 come correspondingly conspicuous and so provide a shin- 

 ing mark that is soon discovered by their insect enemies or 

 by various fungous diseases. 



