A pig rolling around in the mud may look like it's having a gloriously messy time, but there's a good reason for all that wallowing.

Pigs can't rely on sweating to keep cool. They have relatively few functional sweat glands, so when temperatures rise, they need another way to shed heat. Wet mud does the job particularly well. It coats the skin and can keep a pig cool longer than a dip in plain water because the mud stays on the body as its moisture gradually evaporates.

Mud comes with other benefits, too. It can protect a pig's skin from the sun and provide some relief from biting insects and parasites. As dried mud is rubbed or scraped off, it may also help remove irritants from the skin.

And pigs really do seem to enjoy wallowing. The behavior is deeply rooted in their biology: wild boars wallow, too, even when other ways of cooling off are available.

Despite their reputation, pigs aren't inherently dirty animals. Given enough room, they typically keep their sleeping and feeding areas separate from the places they eliminate waste.