Cuba, New York
Crawling on the deck.
No particular plants, just trees and grass.
Your caterpillar is the eastern tiger swallowtail that will turn into a beautiful large yellow butterfly with black striping. Sometimes there are black forms of the female butterflies, such that they look like black swallowtail butterflies.
The orange “horns” are found on all swallowtail larvae. The horns are called osmeteria. When threatened, larvae rear up, stick out the osmeterium, and attempt to smear the potential predator with a chemical repellent.
The dark color indicates it is ready to pupate. When they first hatch, they look like brown and white bird droppings. Then they molt becoming green with the later stages showing the eye spots….the last stage of the caterpillar turns dark brownish-gray before forming a pupa (called a chrysalis for butterflies).
The eastern tiger swallowtail is found east of the Rockies. The adults feed on nectar from many flowers, while the caterpillars feed on leaves of black cherry, magnolia, swamp bay, fringetree and tuliptree.
This insect will not bite nor cause a rash.