The official state insect of Virginia is the Eastern Tiger Swallowtail butterfly (Papilio glaucus). It's easy to see how the males got their name; they're large, bold butterflies with black and yellow stripes, probably the first butterfly species children learn to recognize.
Male Tiger Swallowtails probably don't feel as friendly as humans think they are. When other creatures move into their territory, they fly toward the intruders. Try not to laugh--the draft of their wings might throw a smaller butterfly off course! Like all butterflies, they are on a liquid diet...and they crave mineral salts, so they're not the stereotypical nectar-sipping butterfly. They may perch on your arm and drink the sweat. Considering other things they like to drink, of which polluted puddles are probably the least disgusting, you may not want to let them perch on your arm.
What about those iridescent, glossy (in Latin, glaucus) black butterflies that often fly around with them, avoiding most of the garbage (male Tigers' favorite food is literally garbage) but occasionally joining them at a puddle with a nice film of motor oil on the water? They are not Black Swallowtails. They actually have more black on their wings than Black Swallowtails. They are female Tigers who have inherited the survival advantage of looking a bit like the smaller Pipevine Swallowtails. In areas where pipevines grow, most female Tigers are black.
Here's a nice university-sponsored web site with pictures of these butterflies: