Found it, Hickory Horned Devil,
Scroll down a ways and click on Photo 19.
Two of the largest and most frightening-looking "non-stingers" found on Alabama trees are the hickory horned devil (Photo 19) and imperial caterpillar (Photo 20). The hickory horned devil is the larva of the regal moth (Citheronia regalis - Saturniidae). The full-grown larva is 4 to 5 inches long. It is a solitary feeder on pecan, hickory, walnut, butternut, sycamore, ash, and sweetgum. The caterpillar is normally present from July through September. The imperial caterpillar (Eacles imperialis - Saturniidae) is the larva of the imperial moth. The full-grown caterpillar is 3 to 4 inches long, and appears in two color forms, green (pictured) and reddish brown. The larva is a solitary feeder and is found on a variety of trees, both conifers and hardwoods. Some common hosts are pine, baldcypress, basswood, elm, maple, oak, hickory, sweetgum, and sycamore. Two broods likely occur each year. The caterpillar may be present in early summer but is usually more common in August and September.