Let's start with the most surprising in both looks and toxicity. The puss caterpillar (also called southern flannel moth, pussy moth, tree asp, and asp caterpillar) looks more like a miniature tribble from Star Trek than a larvae, and is just begging to be pet. But it is far from being as cuddly as tribbles. In fact, if you were to touch the puss moth caterpillar you'd get the surprise of your life.
Poisonous spines hidden in the touchably fuzzy surface of the caterpillar will break off and lodge in the skin releasing venom into your system. From here, according to Baylor College of Medicine, "Intense, throbbing pain develops immediately or within five minutes of contact with the caterpillar. Stings on the arm may also result in pain in the axillary (armpit) region. Erythematous (blood-colored) spots may appear at the site of the sting. Other symptoms can include headaches, nausea, vomiting, intense abdominal distress, lymphadenopathy, lymphadenitis, and sometimes shock or respiratory stress. Pain usually subsides within an hour and spots disappear in a day or so -- however, with a larger dose of the venom, it is not uncommon for the symptoms to last up to 5 days."
In other words, it is sooooo not worth trying to pet this fuzzy little guy -- it is one of the most toxic caterpillars in North America.