Below is the Hickory Tussock Moth caterpillar, which is quite prevalent in this region every fall (this particular one was photographed just outside my garage). Despite the black-and-white warning coloration, children and adults often deliberately handle these insects and rapidly develop urticaria and pain at all points of contact. This insect has multiple irritant spines, some of which may contain histamine, and while the reaction is rarely dangerous it is dramatic and very uncomfortable.
Treatment is supportive. In particular, I recommend saturating gauze pads with 1% lidocaine with epinephrine and applying them over areas of irritated skin, and leave in place for at least 20 minutes. This action will treat both the pain and urticaria. With lidocaine, always be mindful of the total dose that the patient can tolerate (5-7mg/kg) even with topical application. Antihistamines are also helpful, as well as brief lesson about warning coloration amongst our animal friends.