japanese weasel description

Japanese Weasel

Mustela itatsi

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia
  • Order: Carnivora
  • Family: Mustelidae
  • Genus: Mustela
  • Species:M. itatsi

 The Japanese weasel (Mustela itatsi) is a mammal of the family Mustelidae. This weasel is often considered a subspecies of the Siberian weasel. However, recent studies have proven that the Japanese weasel is a distinct species.


Gender Weight Lenght Life Expectancy
Male 200-500 grams 25 - 40 cm 3 to 8 years
Female 150-480 grams 20 - 35 cm 3 to 8 years

 What does the Japanese Weasel look like?

Like all weasels, the Japanese weasel has a long, slender body with short legs and a large neck and small head. The Japanese weasel is the largest weasel species. An adult male measures between 45 and 52 cm long, including the tail, and weighs an average of 400 g. Sexual dimorphism is present in this species, females being generally smaller.

The coat is generally golden orange with a lighter coloration on the ventral side and darker spots near the muzzle. In response to the shortening of daylight, Japanese weasels stop producing melanin and their coats turn white and thicken in preparation for winter.

Although their bodies are well adapted to enter tunnels or tight spaces, they are not very efficient at retaining body heat. The weasel must continually search for food to overcome this disadvantage.

japanese weasel appearance

What is the habitat of the Japanese Weasel (Mustela Itasti)?

The Japanese weasel was historically native to three of the four major islands of Japan: Honshu, Kyushu and Shikoku. During the 20th century, it was introduced to most of the other Japanese islands to control the proliferation of rodents. The current distribution includes Hokkaido and most of the Ryukyu Islands.

The Japanese weasel is found in a wide variety of Japanese ecosystems, but mainly in mountainous and forested areas near water. It hunts along rivers, but occasionally ventures into grasslands or areas lightly populated by humans.

japanese weasel map

 What does a Japanese Weasel eat?

Because the Japanese weasel is able to live in a wide variety of habitats, it has a wide range of prey options. Its preferences are generally rodents, amphibians, reptiles, birds and some crustaceans. When prey is scarce, they will eat fruits and berries. On the other hand, if food is abundant, it hides its food to consume it later.


How does the Japanese Weasel reproduce?


In the Japanese weasel, mating takes place from early May to late June. However, if there is an abundance of food, mating can occur until August, producing a second litter during the season. Mating is brief, but can occur several times for each pair. The gestation period lasts about thirty days. The number of pups per litter varies from two to twelve, but on average there are five or six. When the pups reach the age of eight weeks, they are weaned and independent. Sexual maturity is reached at the age of one year.

The female takes care of her young alone, the male leaving her once mating is complete. The mother usually builds the nest in abandoned burrows, and places grasses, feathers and fur from animals she has hunted to make it comfortable. Once the young are born, she feeds them milk until their canines are fully developed and they can eat meat. Once they can hunt on their own, they are considered independent and go off to find their own territories.

The longevity of the Japanese weasel is similar to other members of the genus Mustela. For comparison, a Siberian weasel has lived to be eight years old in captivity. Weasel life expectancy in the wild is highly dependent on food availability. On average, the Japanese weasel lives between two and three years.

What is the behavior of Japanese Weasels?

The Japanese weasel is a solitary animal except during mating season. It is very territorial and aggressively defends its home range against intruders. It is capable of defending itself against larger animals. In addition, once cornered or very frightened, the weasel releases a powerful dose of musk to deter attackers.

The Japanese weasel is an experienced hunter, hunting its prey in all environments such as underground galleries, in trees or even in water. Wherever the prey can go, the weasel will follow it. It is both diurnal and nocturnal.


What are Japanese Weasels predators?

Despite its carnivorous lifestyle, the small size of the Japanese weasel makes it a target for some large predators, mainly raptors such as hawks and owls. Its musky odor makes it less acceptable to predatory mammals.


Are Japanese weasels in danger?


Although their populations are declining slightly, Japanese weasels are listed on the IUCN Red List as Least Concern (LC) due to their wide distribution throughout Japan. The main threat to the Japanese weasel is habitat loss due to residential and commercial development.