Urticating caterpillars give you hives. No, really.

You may recognize the term "hives" as the red, itchy, stinging, swollen areas of skin that have tortured you or someone you know. The technical term for hives is urticaria. And a number of things can cause it.

One cause you probably wouldn't think of is a caterpillar. Urticating caterpillars are moth larvae that get their name from the fact that they sting people in a way that produces urticaria.

These creepy crawlers have hollow spines that hold an irritating fluid that causes stinging and burning in a person's skin. In Georgia, urticating caterpillars show up in the late summer and fall. The two most common in Georgia are the saddleback and puss caterpillars.

Saddleback caterpillar

The saddleback (Sibine stimulea) is the one most often encountered. The full-grown caterpillar is striking. It's about 1 inch long, and the middle of the body is green with a white or cream margin and a large, oval, dark brown spot in the center, also with a white margin. The white-bordered brown spot looks like a saddle and blanket, giving it its name.

Its startling color scheme doesn't hide the fact that it bristles with spines. It has pairs of dark brown, spiny "horns" on the front and rear ends. And in-between are small clumps of spines along the lower margin of the green area.

Saddlebacks are generally solitary feeders. However, early-stage larvae may be somewhat gregarious. They show up in many trees, shrubs and other plants, including corn. But they're most common on oaks, elms, dogwoods and various fruit trees.

Their sting produces an immediate burning sensation, followed by inflammation, swelling and a red rash.

Puss caterpillar

The puss caterpillar (Megalopyge opercularis) looks a little like something the cat might have coughed up. It's hairy. Really hairy. It's more than an inch long, with short, toxic spines hidden underneath its brown or gray fur. The hairs at the rear end form a tail-like tuft, with the head tucked under the front.

Puss caterpillars feed on oaks, pecans, persimmon, fruit trees, roses and other trees and shrubs. They're typically loners, although you may find several on a given tree.

These little dusters only look like harmless hair balls. They actually cause the most painful and severe reaction of any urticating species in the United States.

When your skin brushes against the puss caterpillar, the spines break off, releasing an irritating fluid that produces an immediate stinging, burning sensation. The numbness and swelling that follow may extend to your whole arm or leg in severe cases.

Red blotches may persist for a couple of days, accompanied by a weeping rash. Associated lymph nodes may swell and be tender for 12 to 24 hours. Systemic reactions may include nausea and vomiting.

What to do

If you're gardening, mowing the lawn, picking fruit or working in other ways in which you might brush against urticating caterpillars, wear long pants, long-sleeve shirts and gloves.

If one stings you, treat the symptoms. To remove any spines still in the skin, gently stick a piece of adhesive tape to the site and then pull it away. Applying cold compresses can lessen the pain and swelling.

Over-the-counter pain medications and topical hydrocortisone creams may help. If the symptoms include systemic reactions or don't begin to ease up a couple of days, contact a physician.