Scientific Illustration Resources
Insects
National Audubon Society Field Guide to North American Butterflies
by Robert Michael Pyle
National Audubon Society Field Guide to North American Insects and Spiders
by Lorus J. Milne, Susan Rayfield (Illustrator)
Web sites:
Online Image Databases 
Insects and Spiders
Tree of Life Web Project, provides scientific name for species
Google Image Search, searchable database of images