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This looks like a species of Giant Water Bug, Genus Lethocerus. Unfortunately, I don't think that you will be able to get a specific species due to similarities between them. Here is a link to the bugguide.net page for this insect:
http://bugguide.net/node/view/13706/bgpa...
This is most likely in the genus Lethocerus, but I can't see enough in the image to determine more than family level.