Megalopyge opercularis has a variety of nicknames such as southern flannel moth, puss caterpillar, and the tree asp. Although they look fuzzy and cute, and like something you may want to pick up, they are considered the most highly venomous caterpillars in North America.
The “hairs” of these caterpillars can break off and cause itching, but also hide an unpleasant surprise: sharp spines. The spines are connected to venom gland cells, and function like little hypodermic needles. The pain from injected venom is said to be intense, and lasts at least 12 hours. (Source)