I took this photo about an hour ago in my butterfly garden.
I'm so excited! I'm pretty sure (after checking in my butterfly book) that it's a Giant Swallowtail! This is the first time I've seen one, and it chose my yard. It helps verify that I must be doing some of the right things to attract the critters. :)
They're not kidding when they say "giant"... this thing was as big as my hand (or would be, if her wings were outstretched). She was so lovely, and she kept sipping and sipping from the swamp milkweed you see in the picture. Every once in a while, she would do a circle around me, then go back to the flowers. She even stayed put while I ran to get my camera.
Apparently, they have a caterpillar stage that looks like an orange "bird dropping". So if you see that, let it be! They are more common in the States, especially Florida, because their caterpillar host trees are in the citrus family.
Here in Ontario, though, they feed on the hop tree and the northern prickly ash (both in the same family as citrus trees). It seems these plants are at the northerly end of their range here, so the butterflies are, too. I feel lucky to have had her.