THE TRIBE OF THE ANGLE-WINGS 175 



"These butterflies remain during cool spring nights in 

 places similar to those in which they hibernate in winter, 

 viz., in openings in stone walls, in old out-houses, in open- 

 ings under the bark of trees, etc. They retire to these 

 places with considerable regularity, so that in the open 

 woods, where dozens of individuals may have been seen 

 flitting about, all may have disappeared a, quarter of an 

 hour later. I have watched their retreat with some care. 

 On a clear afternoon in early April I took my stand in a 

 woodland where many Mourning-cloak butterflies were 

 on the wing. They continued actively flying about till 

 approximately four o'clock, when I began to notice a di- 

 minution in their niunbers. By a quarter past four not a 

 butterfly was to be seen. During the fifteen minutes from 

 four o'clock on I followed two to their hiding places. One 

 alighted on the front of a fallen tree and without expanding 

 its wings crept immediately into a large crack in the bark. 

 The second settled on a stone fence and crept into a hole 

 between some loose stones. The period during wliich this 

 occurred was marked not so much by a diminution of 

 light as by a rapid fall of temperature." 



That the habit of lethargy in cold and of resting upon the 

 bark of trees is practically universal with this species is 

 shown by a statement quoted by H. G. Adams in his book, 

 "Beautiful Butterflies," published in England in 1871. 

 The writer quoted says: "In a wood on the summit of the 

 Drachenfels, when the wind was rather keen, I found num- 

 bers resting on the backs of fallen trees in a state of stupor. 

 They made no attempts to escape and when thrown into 

 the air their wings barely opened or flapping feebly eased 

 their fall or enabled them to seek repose on the stem of a 

 rotten trunk." 



