The Mustelidae is a family of carnivorous mammals, that are regarded by some as rather primitive. Many kinds of mustelids are maligned by humans. However, the Mustelidae is among the most successful, beautiful, diverse and interesting families in order Carnivora. Mustelids range from the Least weasel, not much larger than a mouse, which can live in the high Arctic; to the wolverine, a 50-pound animal that can dispatch reindeer, crush bones as thick as the femur of a moose to get at the marrow, and has been known to drive bears from kills; to the ratel, who has a unique symbiosis with a bird called the honey guide bird; to the tropical, largely fruit-eating tayra; to the aquatic otters. Other mustelids include mink, badgers, weasels, polecats, and martens.
The Mustelidae is one of the most species-rich families in order Carnivora, as well as one of the older ones. Mustelid-like forms have existed for the past 40 million years and roughly coincided with the appearance of rodents. Today, many mustelids have evolved in unusual directions. The largest member of the family, the Sea otter, is the most strictly aquatic mammal except for cetaceans (whales), pinnipeds (seals, sea lions and walruses), and sirenians (manatees). In fact, thinking about the terrestrial stoat, the semi-aquatic mink, the more aquatic river otters, the still more aquatic sea otter, the almost completely aquatic pinnipeds and the cetaceans who will die if they come to land, we see mammals who have reached various stages of adapting to an aquatic lifestyle and can imagine how the complete process might occur. The Sea otter is also the only non-primate mammal known to use a tool while foraging. It uses "anvil" stones to crack open the shellfish that form a significant part of its diet. It is a "keystone species," keeping its prey populations in balance so some do not outcompete the others and they do not destroy the kelp in which they live. Just as otters are adapted to swimming, the several groups of badgers are adapted to digging. Many species of badgers and otters have evolved to be social.
Even the more "primitive" mustelids also have noteworthy special adaptations. The fisher, a type of marten, has a unique system to kill porcupines--it targets the face until the animal is so weak it can be flipped over to its vulnerable belly. In some areas porcupines form as much as a quarter of the fisher's diet. The Least weasel, adapted for eating small rodents such as mice and voles, reproduces up to three times a year (unusual for carnivores, who typically reproduce annually) to take advantage of the fluctuations in rodent populations. Because of its small body size and fast metabolism it must eat every few hours to survive, so it runs through multiple cycles of sleep and wakefulness every day.
Mustelids also have some of the most exquisite furs--the mink, the sable (a type of marten) and the ermine (stoat) are all members of the family. This has led to the ruthless slaughter of these animals, especially in the past. One species, the Sea mink (Mustela macrodon) of New England and Canada, was driven to extinction by fur trappers around the same time that the Passenger pigeon was declining. Its appearance and habits are almost unknown because no one seems to have preserved even a single complete specimen, let alone conducted a systematic study. Today, some mustelids are in trouble for other reasons. The Sea otter, who almost shared the fate of the Sea mink, now risks being destroyed by oil spills and the side effects of overfishing; the Black-footed ferret, a relative of the European polecat, suffers from the disappearance of the American prairie; and the wolverine is in a long, slow decline because of habitat destruction and persecution.
Ferrets are kept as pets in many households.