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Papilio polyxenes
North America
This is a beautiful butterfly (I know it's an old spotting but I happened upon it). This looks to be a male Black Swallowtail, Papilio polyxenes. Papilio thoas, wich does look similar does not occur in northern North America. It occurs moslty in south Texas to Brazil. Additionally, the color pattern is a bit different.
Here is a link to info on Papilio thoas:
http://www.butterfliesandmoths.org/speci...
Here is one on Papilio polyxenes: http://bugguide.net/node/view/2636
Hope this helps!