This swallowtail, Papilio thoas, is closely related to our native giant swallowtail, and the two species are almost impossible to tell apart in either the butterfly or caterpillar stage (the caterpillars of both look like bird droppings!). However, giant swallowtail caterpillars eat the leaves of citrus plants, while Thoas caterpillars eat members of the black pepper family.
Like most swallowtails, this is a large, strong butterfly that hovers, much like a hummingbird, rather than landing when visiting flowers for nectar.