Some have established themselves in the wild in Newfoundland, Europe and South America after escaping from fur farms. In Europe, tens of thousand were intentionally introduced by the Soviet Union over a period of several decades, to provide a new game animal for trappers, with disastrous results.

In recent years, animal rights activists have also released several thousands in their attacks on fur farms. Most of these released captive mink quickly died in the wild, preyed on by dogs or run over by cars.

The larger American male will mate with European Mink females earlier in the spring than the males of the same species; the offspring are not born, but the females do not then breed again that season. This has contributed to the decline of the European species. American Mink have also been implicated in the decline of the Water Vole in the United Kingdom and linked to the decline of water fowl across their range in Europe. They are now considered vermin in much of Europe and are hunted for the purpose of wildlife management.

Their long slim body is covered in glossy, thick dark brown or black fur with a white patch under the chin. They have short legs with partially webbed feet, which make them excellent swimmers.

They can be found in wooded areas and fields near streams and lakes. They dig burrows in river banks or take over dens abandoned by other animals.

They feed on small mammals, fish, crayfish, frogs and other amphibians, also sometimes eating birds, insects and earthworms. These animals are mainly active at night and do not hibernate. Their predators include coyotes, the Great Horned Owl, red foxes and wolves. They are also trapped for their fur. Their numbers have been reduced due to loss of habitat and the effects of pollution on their aquatic food supply.

They are usually solitary animals. Mating occurs during winter; males and females may have more than one partner. Females give birth to 3 or 4 young during early spring.