Not a butterfly, it's a Luna Moth, Actias luna. Most often seen at night, near bright lights, this one had clearly chosen the boat as a day time hiding place. It didn't like the light, and given a chance, worked itself into some towels that we had handy, so we brought it home for a photo shoot.
Life History: Adults are very strong fliers and are attracted to lights. Mating takes place after midnight, and egg-laying begins that evening. Females lay eggs in small groups or singly on both surfaces of host plant leaves. The eggs hatch in about one week and the caterpillars are sedentary and solitary feeders. Leaves and silk are used to spin papery brown cocoons in litter under the host plant.
Flight: One brood from May-July in the north, two to three broods from March-September in the south.
Caterpillar Hosts: A variety of trees including white birch (Betula papyrifera), persimmon (Diospyros virginiana), sweet gum (Liquidambar styraciflua), hickories (Carya), walnuts (Juglans), and sumacs (Rhus).
Adult Food: Adults do not feed.
Habitat: Deciduous hardwood forests.
Range: Common. Nova Scotia west to Saskatchewan and eastern North Dakota; south to central Florida, the Gulf Coast, and eastern Texas.