Later this year, Laurie Collins and Kathy Engle will be teaching Butterfly Gardening, including the host plants needed to feed the caterpillars. Some info from the link above,
After mating, female tiger swallowtails lay eggs on leaves of host plants. Host plants are the plants that caterpillars will eat. Host plants of Eastern Tiger Swallowtails include Yellow Poplar, Black Willow, Black Cherry, American Hornbeam, Red Maple, Spicebush, American Elm, and Sassafras.More information on Butterfly Gardening here and here.
When caterpillars first hatch, their colors look a lot like bird poop. This helps camouflage them. As they get older, they turn green with a large head and bright eyespots. The eyespots aren't really eyes. They are probably there to scare away predators, or to make them attack the wrong part of the butterfly. A butterfly can lose part of a wing and still survive.
Update June 21: Check out earlier posts on butterflies, including Kathy Engle's wonderful "Garden with Wings" series from 2010. Then there's these videos, with others showing off their fascination with Butterflies, and one lucky fellow, too.