Chuckwallas are large lizards found primarily in arid regions of the southwestern United States and northern Mexico. Chuckwallas are stocky, wide-bodied lizards with flattened midsections and prominent bellies. Their tails are thick, tapering to a blunt tip. Loose folds of skin characterize the neck and sides of their bodies, which are covered in small, coarsely granular scales. The common chuckwalla (Sauromalus ater) measures 15 3/4 inches long. Harmless to humans, these lizards are known to run from potential threats. When disturbed, a chuckwalla wedges itself into a tight rock crevice and inflates its lungs to entrench itself.