High Quality Content by WIKIPEDIA articles! The ferret is a domesticated mammal of the type Mustela putorius furo. Ferrets are sexually dimorphic predators with males being substantially larger than females. They typically have brown, black, white, or mixed fur. They have an average length of 20 inches (51 cm) including a 5 inch (13 cm) tail, weigh about 1.5–4 pounds (0.7–2 kg), and have a natural lifespan of 7 to 10 years.