MUSTELIDAE - badgers, otters, weasels, and relatives

This family, containing approximately 65 species, is the largest in Carnivora, being twice as large as the next largest family, the Herpestids. They are found on all continents except Australia and Antarctica. They are also not found on most oceanic islands, such as Madagascar, most of the Philippines, the West Indies, New Zealand, and New Guinea.  Members of this family include weasels, stoats, polecats, mink, marten, fishers, wolverines, otters, badgers and others. While many authors have traditionally considered skunks a subfamily within Mustelidae, recent molecular evidence indicates that skunks do not lie within the mustelid group and instead are recognized as a single family, Mephitidae.

Mustelids inhabit all continents except Australia and Antarctica, and do not occur on Madagascar or oceanic islands. Members of this group can be found in diverse habitats, which include both terrestrial, aquatic and marine environments. Mustelids are mainly carnivorous, with various members of the family exploiting a great diversity of both vertebrate and invertebrate prey. Mustelids are generally proficient hunters; some weasels can take prey larger than themselves. Members of this family often hunt in burrows and crevices, and some species have evolved to become adept at climbing trees (e.g., marten) or swimming (e.g., sea otters, mink) in search of prey. (Nowak, 1991; Sato et al., 2003; Vaughan, Ryan, and Czaplewski, 2000; Whitaker and Hamilton, 1998)

Generally, mustelids have elongate bodies with short legs and a short rostrum, as typified by weasels, ferrets, mink, and otters. Wolverines and badgers have broader bodies. An order of magnitude difference in size exists between the smallest and largest mustelid species. The smallest species is the least weasel (Mustela nivalis), weighing between 35 and 250 grams. Wolverines (Gulo gulo) and sea otters (Enhydra lutris) reach 32 kg and 45 kg, respectively. All mustelids have well developed anal scent glands, which serve various functions, including territorial marking and defense.

The morphological characters considered to unite all mustelids are enlarged anal scent glands, the loss of the second upper molar, and the loss of the carnassial notch on the fourth upper premolar. Mustelids share these characters with skunks, the main reason for their historical inclusion in the family. These characters may be the result of convergent evolution, however. For example, all carnivores have enlarged scent glands, and those of skunks are much more enlarged than in Mustelidae. Furthermore, the anal scent gland in skunks is associated with a nipple, rather than a duct as in Mustelidae.

The mustelids are generally small to medium sized animals. They range in size from the least weasel, weighing 35-70 g (1-2 oz.) to the giant otter, which can weigh up to 35-40 kg (77-88 lb.). Male mustelids are usually about 1/4 larger than females. They generally have a slender, long body structure set on short legs. Their tails are generally long. They have short, rounded ears set low on their heads. All mustelids have highly-developed anal glands, which are defensive weapons in such species as the skunk.

They can be plantigrade or digitigrade. All feet have five toes. In some species, the claws are partially retractable. Claws in general in the mustelids tend to be short and curved. Male mustelids have a well-developed baculum.

Mustelids can have between 28-38 teeth. In each jaw they have 6 unspecialized incisors, 2 long canines, between 2-4 premolars which includes the well-developed carnassial, and usually 2 molars. The upper molars are constricted in the middle, giving them an hourglass shape. The genus Enhydra is the only genus to have 4 lower incisors.

Most mustelids are carnivores. Some will include insects in their diet, and some will feed on fruit and honey. They are quick, agile, and strong predators, with well developed senses of smell and hearing.