Unknown Beauty

While visiting a friend in Pennsylvania, I noticed this beauty on a butterfly bush. Can you tell me what it is and give me more information about it?

—Shirley Mathews, Wilmington, Delaware

Tom: The butterfly is a female tiger swallowtail. Females have a lot more blue on their hind wings than males, so they are easy to distinguish. These butterflies should be common in your area. They feed on cherry and tulip poplar trees as caterpillars, and the adults often visit flower gardens to obtain nectar. If you want to attract them, try planting butterfly bush (as your friend did). It's one of the best nectar-producing plants in summer gardens.