Up until the turn of the 19th century, ferrets remained one of man's best alleys for eradicating rats, mice and rabbits. The use of ferrets declined with the invention of inexpensive baits. Currently, the number of ferrets kept as pets in the United States is not far behind dogs and cats. Documentation for ferreting during the Middle Ages is spotty and in need of vast improvement. This need for further documentation offers the opportunity for extensive original research.
Ferrets are a domesticated species of weasels.
Weasels form a rather large Family of animals, the Mustelidae. It's Sub-Family Mustelinae contains 34 species. These include the grisons, martens, mink, polecats and weasels. They are terrestrial hunters of small vertebrates, although some such as the martens are excellent climbers. Active at night, weasels generally hunt alone, capturing rodents, fish, frogs, birds and birds' eggs.