Affinities and Origins of the Northern and Montane 

 Insects of Western North America 



Herbert H. Ross 



Illinois Natural History Survey, Urbana 



1 he subjects of this paper are the insects 

 belonging to the cool-adapted biota and occupying an ecological 

 band comprising essentially the cool-temperate and arctic regions. 

 The arctic region comprises both the tundra of the Arctic and the 

 alpine tundra found above timberline in subarctic areas. The cool 

 temperate region comprises the taiga and its equivalents — the 

 northern coniferous spruce and pine forests and various higher- 

 elevation forests toward the south. In North America today this 

 double band — cool temperate and arctic — extends in a wide swath 

 across roughly the northern third of the continent and extends 

 southward as islands at higher and higher elevations, through the 

 mountain chains of eastern and western America. In the West these 

 cool-temperate islands are larger and occur much farther south than 

 in the eastern part of the continent. 



A large number of insect species are abundant in both taiga and 

 tundra, and are almost entirely restricted to these two major 

 ecological formations. These insects represent many orders and 

 families, including such well-known types as caddisflies, sawflies, 

 and mosquitoes. Although today these many species of various 

 families form what appears to be a closely knit ecological aggre- 

 gation, they must have arrived in this general area of the continent 

 by diverse paths and at different geologic times. 



Concerning this cool-adapted biota of western North America, 

 we can deduce that some elements arrived from Asia, that other 

 elements spread westward from the eastern parts of North America, 

 and that still others spread northward from the more tropical 

 areas to the south. Present information gives evidence of dis- 

 persals of living genera dating from Cretaceous time to practi- 



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