This beautiful caterpillar colors are pastel rainbows including green, blue, pink and yellow with a length of less than an inch. This caterpillar is also rather flat and has four dark thorn clusters near the back end. The poison released by thorns causes a very severe reaction and needs medical treatment as soon as possible. Spiny Oak Slug Caterpillar likes to eat dates, willow, oak, hackberry and chestnut along with other trees and smaller woody plants. This caterpillar species can be found in the forests of southern Quebec to Maine and south of Missouri, Texas and Florida.