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Cover photo of three species of caterpillars

Caterpillars of Pacific Northwest Forests and Woodlands

by

Jeffrey C. Miller
Introduction
Insects are notably abundant in a wide variety of habitats. The moths and butterflies (Lepidoptera), in particular, are obvious in addition to being well represented among the total number of insects from a given site. The caterpillar is the actively feeding immature stage of moths and butterflies and is perhaps less obvious at first glance but can be abundant on certain plants at certain times of the year. In addition to being abundant, caterpillars are diverse in the number of species present, their appearance, behavior, and life cycle requirements.

Identifying field-collected caterpillars to the species level is essential to performing natural history observations and conducting detailed ecological studies on caterpillars and host plants, parasitoids and host caterpillars, and using caterpillars as indicator species in assessing environmental impacts. Diagnostic keys for identifying species of caterpillars in the Pacific Northwest are not available. In fact, few scientific papers and books can be found that illustrate caterpillars of this region. Stevens et al. (1984) is one of the few sources available for illustrations of caterpillars in the Pacific Northwest. Certain books provide excellent photographs of common caterpillar species of different regions, such as the Canadian Provinces (Ives and Wong 1988), the Appalachians (McCabe 1991), and eastern deciduous forests (Wagner et al. 1995). Some of the species illustrated in these books also occur in the Pacific Northwest; however, Oregon alone contains over 1600 species of Lepidoptera, and a majority of the Pacific Northwest species do not occur east of the Rocky Mountains.

This booklet is a field guide with keys to the identification of caterpillars commonly found in forests and woodlands of the Pacific Northwest. It contains a brief section on the natural history of caterpillars and describes variations in morphology, color, and pattern that are used to identify caterpillars. It also provides details on how to collect and rear caterpillars, and how to photograph and preserve specimens. Included are a section on nomenclature and a description of the families most commonly found in the Pacific Northwest.

The Pacific Northwest, as considered here, consists of Oregon, Washington, and Idaho. This region contains numerous mountain ranges, part of the Great Basin, the Columbia River Basin, part of the Snake River, the Puget Sound, and the Willamette Valley. The vegetation in this region is diverse, including a flora adapted to coastal, desert, and alpine environments. The dominant forest tree is Douglas-fir, with ponderosa pine and lodgepole pine also prevalent. Caterpillars that feed on the understory vegetation of these forests are the focus.

This resource is based on the following source: 
Miller, Jeffrey C.  1995.  Caterpillars of Pacific Northwest Forests and 
     Woodlands.  U.S. Department of Agriculture, Forest Service, National 
     Center of Forest Health Management, Morgantown, West Virginia.  
     FHM-NC-06-95.  80 pp.

This resource should be cited as: 

Miller, Jeffrey C.  1995.  Caterpillars of Pacific Northwest Forests and 
     Woodlands.  U.S. Department of Agriculture, Forest Service, National 
     Center of Forest Health Management, Morgantown, West Virginia.  
     FHM-NC-06-95.  80 pp.  Jamestown, ND: 
     Northern Prairie Wildlife Research Center Online.  
     http://www.npwrc.usgs.gov/resource/2000/catnw/catnw.htm 
     (Version 21APR2000).

Table of Contents
USDA logo   United States Department
of Agriculture		 Forest Service December 1995

A reprint of this resource can be obtained at http://www.fs.fed.us/foresthealth/technology/order.shtml. Specify order no. FHM-NC-06-95

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