Giant Swallowtail visited our backyard, butterfly habitat today. I spent an hour hunting down information on the internet to identify it. For a while, I thought it might be a Thoas Swallowtail, but its range is South America through Texas (only sometimes in Oklahoma and Kansas), so that didn't sound right. This set of photographs helped me correctly identify it as a Giant Swallowtail (I LOVE the internet). The difference is the number of spots on the trailing edge of the forewings. Thoas has 4 marginal spots on the trailing edge of the forewing; whereas the Giant has only 3.
Can you count the spots on the separated wings in the enlarged photo below? You can also see some damage to its left forewing.