Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
Caterpillars of Eastern North America: A Guide to Identification and Natural History (Princeton Field Guides)
By David L. Wagner
Princeton University Press, 1-496, 2010
ISBN: 0691121443
Cite: 873788 with citation markup [cite:873788]
Out of print first edition (July 25, 2005) is in the guide here. (1)
2010 edition available at Amazon.

Some preview pages at Google books

Looks to us like the 2005 edition
is still available at Amazon for about $20. Is the new edition so different that it would be worth paying the $50 for it?

 
Amazon has the 2010 edition for $22.54
Not sure of the differences, I do not have the 2005 edition.

Amazon.com 2010 edition for $22.54

Amazon.com 2005 edition

Used 2005 editions can be found cheap on Ebay.

 
I'm confused
both of your links seem go to the 2005 addition, the first to the paperback and the second to the hardcover addition.

Both pages say: "Publisher: Princeton University Press (August 14, 2005)"