6 UNITED STATES NATIONAL MUSEUM BULLETIN 276 



Dyar was correct in suspecting that pluviale would grade into fragile^ 

 and a similar situation has been found for several other "species" of 

 Malacosoma described from western North America. 



In short, ever since the species of Malacosoma first were described 

 (and up to the present), identification of adult Malacosoma has been 

 difficult or impossible. Larval characters have been supposed to be more 

 reliable, but doubts have been expressed about them, too. This is 

 particularly true of the Malacosoma which occur in the western part of 

 North America. 



A systematic study of Malacosoma based largely on adult morphology 

 was completed by the senior author in 1958 (Stehr, unpublished M.S. 

 thesis). It resulted in four species clearly being recognized in the United 

 States and Canada, plus a fifth group of described species which could 

 not be separated from one another by any known adult morphological 

 characters, but which were supposed to be quite distinct as larvae. 

 As only limited numbers of larvae were available, and most of them 

 were not positively associated with adults, it was impossible to determine 

 how closely the supposedly constant larval difTerences were correlated 

 with adult differences. 



Because of the lack of any specimens from many areas, the limited 

 numbers of larvae, the even more limited numbers of lar\'ae associated 

 with adults, and the scarcity of reliable information about egg masses, 

 tents, host plants, distribution, etc., it was decided that the only way 

 to obtain a better understanding of these western North American groups 

 was to study them in the field. The results of this field work, carried out 

 in 1960, 1961, and 1962, form a large part of the information contained 

 herein. 



Summary of Results 



The classification for the North American Malacosoma presented 

 below is a result of this study. Based on available information, it is 

 believed that this classification best represents the evolutionary stage 

 attained by these populations, and it is given here in brief outline form, 

 along with an indication of the status change of the names. 



The most important changes are the reduction of M. ambisimile, 

 M. pluviale, M. lufescens, and M. fragile to subspecies of M. calif ornicum 

 (Packard), the name which has priority, and the elevation of M. 

 incurvum (Henry Edwards) to a species again. Actually, Packard was 

 correct when he stated on several occasions his belief that several of 



