The name Mustelidae derives from the Latin word for weasel, but this diverse family of carnivores also includes otters, badgers and wolverines (gluttons). In all, there are generally considered to be 57 species in 8 genera – but through the use of genetic coding, this is likely to change. Already the skunk has been moved to a different family.
The physical characteristics of mustelids include relatively short legs and a long body. Most species are solitary (except for the European badger (Meles meles) and the sea otter (Enhydra lutris) and nocturnal (except the sea otter) although many species will also be active by day in areas where they are not disturbed by human activities. With the exception of the sea otter, mustelids possess anal scent glands that produce a strong-smelling secretion used for marking territory and communicating with the opposite sex.
The larger species in particular have thick fur – the sea otter has the densest fur of any animal. Various species have been hunted for their fur, and at least one species, the Sea Mink (Neovison macrodon) of North-eastern America was hunted to extinction. Populations of many others, such as the sable (Martes zibilina found across Russia) suffered for their fur. Other species, such as the mink (Neovison vison), have been bred in captivity specifically for the fur trade. They have been persecuted by gamekeepers protecting their grouse and pheasants, yet the European polecat/ferret (Mustela putorius) in particular has been domesticated for its ability to hunt rabbits.
Mustelids vary considerably in size. The least weasel (Mustela nivalis) of Europe, North America and North Africa is small enough to run into mouse-holes, yet is capable of killing a rabbit. Conversely, the giant otter of South America can measure up to 2.4m, and sea otters can be heavier than 45 kilograms. Males are generally larger than females.
Mustelid-like animals first appeared in the fossil record about 40 million years ago, about the same time as primitive rodents. Both types of animal have evolved to fill ecological niches all over the world.
Because of their solitary life-styles, males and females come together only rarely, and mating can take place at any time of year. However, to avoid the young being born in, for example, bad winter weather or summer draught, the embryo remains dormant in the uterus until the female has enough food available to carry the pregnancy. It also means she can mate while nursing cubs, and the new cubs will not be born until the older ones have been weaned. Once conditions are favourable, the embryo implants, and pregnancy begins.
While trapping these animals for fur is less of a problem in the 21st century, these animals face other hazards. Sea otters, and river otters living on the coast, are vulnerable to oil spills. The black-footed ferret of the American prairies is threatened by habitat destruction. The European badger is protected in Britain because it was caught for the barbaric “sport” of badger baiting.
Because these animals are often nocturnal, and have large territories, they are difficult to study. There is still much to be learnt about them.