The spiny oak slug is a vivid green caterpillar in the family Limacodidae about 3/4" (2 cm) long when mature. The caterpillar has a colorful body (colors vary enormously) with spiny tubercules along the back and sides. The spines have a toxic venom released by the slightest touch which can cause a painful skin reaction. Their legs are shortened and the prolegs are reduced to suction cups. They eat a variety of deciduous trees and shrubs, including apple, ash, basswood, beech, birch, blueberry, cherry, chestnut, hackberry, hickory, maple, oak, poplar, sycamore and willow.

Our parents always told us to stay away from spiny oak slugs. However, we often tried to catch them and place them in a jar to show other kids about our courage.