The saddleback caterpillar, Sibine stimulea, is the larva of a species of moth native to eastern North America.
It is also known as the "packsaddle".
These caterpillars have a pair of fleshy "horns" at either end, and these, like much of the body, bear urticating hairs that secrete an irritating venom. Stings can be very painful. They can cause swelling, nausea, and leave a rash that can last for days