Tiger swallowtails are large butterflies (they can have a wingspan up to 6 inches), and their black-and-yellow pattern is hard to miss. They have slightly different markings depending on whether they're male or female. The female has more blue on its bottom wings; males have little to no blue. (Just remember, blue is for...girls.) It must be this blue that Linneus was referring to when he gave this butterfly its species name, Papilio glaucus: "glaucus" can mean cerulean blue.
Remarkably, females can also be almost entirely black. There is some speculation that this might be mimicry of the pipevine swallowtail, which is much rarer in the DC area. It's also easy to confuse the black form of female tiger swallowtails with other black-colored swallowtails, such as the spicebush and black swallowtails. If you compare the two pictures on the right of the post, you'll see the edges of the wings are almost identical, but the blue is less pronounced. (Spicebush swallowtail has light blue, not yellow, spots on the edges of the wings; black swallowtail has more yellow on the wings.) They're all lovely.
In your yard: To attract tiger swallowtails temporarily, plant nectar flowers. But to really support them, plant one of their host plants -- which will provide the leaves the caterpillars need to eat. These include several trees; black cherry and tuliptree are favorites.
In the wild: You'll see tiger swallowtails in both woods and open fields. We've noticed they like to fly over trails and streams, perhaps because there are fewer obstacles. They sometimes will "puddle" in a sunny, muddy area, where they absorb minerals from the mud.
Sources for this post:
- Douglas Tallamy, Bringing Nature Home: How You Can Sustain Wildlife with Native Plants
- Amy Bartlett Wright, Peterson First Guide to Caterpillars of North America