Observe the body. Weasels vary in size. The small least weasel averages 8 inches in length, and the short-tailed weasel measures 13 inches. The long-tailed weasel is the largest, running to 16 inches. Weasels are long and slender with short legs; their hind legs are only about half as long as their bodies, and the forelegs are noticeably short as well.
Check the tip of the tail. Long-tailed and short-tailed weasels have a black tip. Least weasels lack this identifying trait.
Look at the ears. A weasel's ears are rounded.
Note the color of the animal. Weasels are brown on top, with a white-yellow underside. Those inhabiting colder or mountain areas turn white in winter.
Observe the animal as it runs. Weasels have a distinctive, bounding gait, with the hind feet typically falling almost exactly where the front feet were.
Check for the presence of anal scent glands. All weasels have them.