Identify Pipevine Swallowtail

My son and I were at a national park in West Virginia when we saw these butterflies. Can you tell us what they were?

—Tonya Fraczek, Flat Rock, Michigan

Tom: The butterflies you saw were pipevine swallowtails. They are a very common sight in West Virginia, especially in the mountainous areas. This is where their host plant, Dutchman's pipe, grows on trees along the roads. Since Dutchman's pipe is a toxic plant, very few predators will eat pipeline swallowtails. Those you saw were males. They like gathering in groups, called puddling, to sip nutrients and moisture from the soil.