156 UNITED STATES NATIONAL MUSEUM BULLETIN 2 76 



boundary, although c. pluviale occurs on the east side in some places, 

 and in the foothills of the Canadian Rockies in Alberta. Across central 

 Canada the southern boundary closely follows the prairie-boreal forest 

 ecotone. To the south c. pluviale is replaced by M. californicum lutescens. 

 See "The pluviale-lutescens relationship" (page 60) in the section on 

 crosses for a discussion of M. californicum pluviale and M. californicum 

 lutescens in Canada. Near Winnipeg, Manitoba, c. pluviale''?, distribution 

 meets the northwestern extreme of M. americanum^s distribution. From 

 Winnipeg eastward there is a slight overlap between c. pluviale to the 

 north and americanum to the south, but there is no indication that they 

 ever interbreed. The factors which prevent either one from invading 

 the other's territoiy more extensively are unknown. For an account of a 

 similar situation, see the discussion of the relationship between M. 

 californicum lutescens and M. americanum under "comments" for 

 americanum (page 115). 



COMMENTS. — In the past when c. pluviale was regarded as a species 

 it had been given the common name of the "western tent caterpillar." 

 The Canadians, however, have established that it extends as far east as 

 Quebec, and it probably will be found all the way to the Atlantic 

 Ocean, so the name is hardly appropriate. The name "western tent 

 caterpillar" can most appropriately be applied to all the populations of 

 M. californicum (including all subspecies) since they occupy virtually all 

 of the area west and north of the area occupied by M. americanum, the 

 eastern tent caterpillar. If a common name is desired for c. pluviale 

 (there is no need for one) it should be called the "northern tent cater- 

 pillar" since this is more truly what it is. See Appendix III for a dis- 

 cussion of common names (page 289). 



The Bog Populations of M. californicum pluviale 



This form of f. />/«wa/« was first reported by Grant (1957) and re- 

 corded as occurring over a large part of central and northern British 

 Columbia. It was reported to feed only on Betula glandulosa and one 

 or two species of willows growing in association with it. It was not 

 found in nearby upland forests even though they usually contained 

 many of the hosts which are quite acceptable to more southern popula- 

 tions of c. pluviale. The basic larval color pattern was reported to be 

 predominantly black (fig. 372), but with some individuals having the 

 conspicuous orange markings characteristic of more southern popula- 

 tions (figs. 370 and 371). The egg mass was reported to be laid as a 

 band encircling the twig in contrast to those of c. pluviale in southern 

 British Columbia, which usually do not form a complete band. Egg 

 masses were found only within 2 feet of the ground, and they were laid 



