Listed below are several of the books that I use to identify specimens. Most are still available but some of them are out of print. I have also included several links to web sites that I use. Most of the books listed can be found at book stores or at Bio-Quip. Bio-Quip is a good source for books and collecting supplies. There are other sources but I generally find what I need at Bio-Quip.
Moths of Eastern North America - Charles V Covell, Jr. This book was republished by the Virginia Museum of Natural History.
Checklist of the Lepidoptera of America North of Mexico - Ronald W Hodges
Fascicle of the Moth of North America. There are several volumes covering the various families.
Butterflies and Moths of Missouri - J. Richard and Joan E. Heitzman. Published by the Missouri Department of Conservation.
Caterpillars of Eastern North America - David L Wagner.
Insects in Kansas - Published by Kansas Department of Agriculture
A Field Guide to the Tiger Beetles of the United States and Canada - Pearson, Knisley, and Kazilek Published by Oxford University Press.
Field Guide to Northeastern Longhorn Beetles - Douglas Yanega - Published by Illinois Natural History Survey
The Cicindelidae of Canada- J B Wallis Published by the University of Toronto Press
The Carrion Beetles of Nebraska - Brett C Ratcliffe Published by University of Nebraska State Museum
American Insects - Ross H Arnett, Jr Published by Van Nostrand Reinhold Company
American Beetles - Two Volumes Published by CRC Press
Moths of Maryland - http://www.marylandmoths.com/index.html
North American Moth Photographers Group at Mississippi State University - http://mothphotographersgroup.msstate.edu/MainMenu.shtml
Butterflies of Iowa - Dennis Schlicht and Jeff Nekola ISBN 1-58729-533-4