Web Resources for Butterfly and Moth Identification
Butterflies of America is a comprehensive image archive, currently including all American butterfly species and subspecies from the Arctic Circle to Panama, and the Caribbean Islands (except Trinidad and Tobago). As of January, 2011, over 100,000 images are posted to the site. Butterflies of America is especially useful for identifying northern Neotropical Hesperiidae, Lycaenidae and Riodinidae.
A very useful online identification tool is the Butterflies guide of the IDnature guides series.
BugGuide is a good resource for butterflies or moths. A few web sites that may be able to help with butterfly identification are Cirrus Digital Imaging (photographs of butterflies and moths), The Butterfly Website, TheButterflySite.com, and What's That Bug?. If you are trying to identify a skipper (family Hesperiidae) in the Northeastern United States or southeastern Canada, check out Skippers of the Northeast, a handy set of videos that will guide you through skipper identification.
If you are trying to identify a noctuid moth in or around California, and if you have some expertise in moth anatomy, you may find the California Department of Food & Agriculture Plant Pest Diagnostics Center website of value.
Visit the Links page for other sites that offer photographs and distribution maps.
(Not currently available) The Lepidoptera Wing Pattern Identification System (LepWing ID) uses interactive pattern recognition technology to help researchers quickly and accurately identify species of moths and butterflies. This system was developed by Jeff Miller, a professor in Oregon State University's College of Agricultural Sciences, and colleague Hans Luh, a senior research associate with the university's Integrated Plant Protection Center. This pilot project allows users to compare a digital image of a specimen against a library of more than 1,600 photos.
Web Resources for Caterpillar Identification
First, try the Caterpillar Guide of the IDnature guides series, which offers step-by-step assistance.
For resources with a regional focus, try Caterpillars of Pacific Northwest Forests and Woodlands or Caterpillars of Eastern Forests. Both of these illustrate common moth and butterfly larvae of the respective regions, with emphasis on those that are economically important. The northwestern guide contains a key that enables the user to identify a specimen based on morphological characteristics. Its use requires the reader to learn some scientific terminology and examine the specimen quite closely, often with a magnifying glass. The eastern guide is organized by family, and the reader will have to search it photo by photo; to make it easier to read, a photo thumbnails feature has been added to this resource.
Be aware that a caterpillar may change dramatically in appearance from one growth stage (or "instar") to another. Most of the photos provided in these resources are of late instar caterpillars. Thus you may have to rear a caterpillar in captivity until it enters its last instar in order to identify it. Be sure to note the host plant on which you found your caterpillar. Many butterfly books include a host plant index that may provide valuable clues to the caterpillar's identity. If you know the scientific name of the plant the caterpillar was eating, you can sometimes figure out what you have at the Caterpillar Hostplants Database. Finally, do not overlook the folks at your local extension office; they may be familiar with some caterpillars in your local area and may be very helpful.
Books and Field Guides
Most libraries or bookstores have or can easily obtain field guides to the Lepidoptera. Some that you may find especially useful are:
Covell, C.V., Jr. 1984. A field guide to the moths of eastern North America. Houghton Mifflin Co., Boston.
Opler, P.A. 1994. Peterson first guide to butterflies and moths: a simplified guide to the common butterflies and moths of North America. Houghton Mifflin Co., Boston.
Opler, P.A. and V. Malilul. 1998. A field guide to eastern butterflies. Houghton Mifflin Co., Boston.
Powell, J.A. and P.A. Opler. 2009. Moths of Western North America. University of California Press. 383 pp.
Wagner, David L. 2005. Caterpillars of Eastern North America, Princeton University Press, Princeton, NJ.
Wright, A.B. 1993. Peterson first guide to caterpillars of North America. Houghton Mifflin Co., Boston.