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. 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.
A Field Guide to the Tiger Beetles of the United States and Canada - Pearson, Knisley, and Kazilek Published by Oxford University Press. Isbn 0-19-518156-5
American Beetles - Two Volumes Published by CRC Press ISBN 0-8493-1925-0 and 0-8493-0954-9
American Insects - Ross H Arnett, Jr Published by Van Nostrand Reinhold Company
Butterflies and Moths of Missouri - J. Richard and Joan E. Heitzman. Published by the Missouri Department of Conservation.
Butterflies of Iowa - Dennis Schlicht and Jeff Nekola ISBN 1-58729-533-4
Caterpillars of Eastern North America - David L Wagner ISBN 0-691-12144-3
Checklist of the Lepidoptera of America North of Mexico - Ronald W Hodges
Fascicle of the Moths of North America. There are several volumes covering the various families.
Field Guide to Northeastern Longhorn Beetles - Douglas Yanega - Published by Illinois Natural History Survey
Insects in Kansas - Published by Kansas Department of Agriculture
Iowa Roadway Trust http://www.iowadot.gov/lrtf/index.html
Moths of Eastern North America - Charles V Covell, Jr. This book was republished by the Virginia Museum of Natural History.
Olethreutine Moths of the Midwestern United States - ISBN 978-0-86727-160-7
Owlet Moths of Ohio - ISBN 0-86727-110-8
Peterson Field Guide to Moths of Northeastern North America - David Beadle & Seabrooke Leckie. ISBN - 978-0-547-23848-7. This book has photos of live specimens.
The Carrion Beetles of Nebraska - Brett C Ratcliffe Published by University of Nebraska State Museum
The Cicindelidae of Canada- J B Wallis Published by the University of Toronto Press
The Cutworm Moths of Ontario and Quebec - ISBN 0-660-00514-X