The winter moth Scoliopteryx libatrix 

 is found in the northern latitudes of North 

 America, Europe, and Asia. Sometimes 

 called "the herald" because it is seen in 

 the spring before other insects, the 

 moth has been found hibernating in deep 

 crevices in the rock. 



Frithjof Skibbe; Oxford Scientific Films 



completing both the larval and pupal 

 stages before all the birds return. Then 

 they drop to the ground, bury themselves, 

 and go into suspended animation through- 

 out the summer. 



These moths' predilection for cold- 

 weather activity seems to have evolved 

 fairly recently, because their coloration — 

 ranging from charcoal gray to chocolate 

 brown, sierma, white, yellow, and tan — 

 still carries the imprint of a long history of 

 bird predation. I wondered if winter moths 

 would seek the "right" color bark to rest 

 and remain hidden on, as the summer 

 moths do. To find out, I placed twelve sec- 

 tions of birch, cherry, pine, maple, black 

 locust, and elm trunks in a large outdoor 

 cage, and in the evening I released 173 

 winter moths into the enclosure. The next 

 morning not a single moth could be found 

 on a tree trunk. I searched for six hours 

 among the leaves on the ground and found 

 twenty of them. Because they could not 

 escape the enclosure, I presumed that the 

 rest were hiding in the leaves as well. This 

 explained why I had only seen winter 

 moths on days when the snow cover had 

 partly melted; they had been trapped be- 

 neath the snow-covered leaves. Dale 

 Schweitzer has measured temperatures 

 beneath the leaves on the ground during 

 the winter and found that at night (espe- 

 cially when the ground is snow covered) 

 the temperatures rarely fall below 37° F. If 

 the winter moths in northern New England 

 rested on tree trunks (as their summer an- 

 cestors undoubtedly did), they would 

 often be exposed to temperatures low 

 enough to kill them instantly. Camouflage 

 has become irrelevant beneath the carpet 

 of leaves, where the moths now rest in rel- 

 ative warmth. Their colors, which have 

 probably changed little since they 

 switched to a winter life style, are now 

 "fossil" adaptations to a previous stage in 

 their evolutionary history. 



When I saw my first shivering winter 

 moth on a maple log that November 

 evening years ago, the moth seemed mag- 

 ical. It had traveled a different evolution- 

 ary path than the summertime moths, and 

 that had made all the difference. D 



48 Natural History 2/94 



