Mustela itatsi

The Japanese weasel is a larger weasel, with adult males measuring between 45-52cm from head to tail and weighing an average of 400g. The Japanese weasel has the most sexual dimorphism of the genus, with females generally being smaller, only 68% of the male's body length and only 30% of the body weight. The Japanese weasel, like all weasels, has an elongated body, which is well suited for navigating tunnels and caves and getting into tight spaces. The legs are short, with a stocky head and neck. Their fur is usually golden yellow on their upper body, with a lighter colour on their belly and a darker colour on their face. Before winter arrives, in response to the shortening of daylight hours, the weasel stops producing melanin, and their fur turns white and thicker in preparation for the winter.

The Japanese weasel is endemic to Japan and is native to Honshu, Kyushu, Shikoku, Sado, Oki Islands, Izu Oshima, Awaji, Suta, Iki, Goto, Yaku and Tana. It was introduced to Hokkaido in the 1880s and was introduced to about 50 small islands in Japan, including Hitachi Island, Ruiben Island, Izu Island (Miyake Island, Yae Island, Aoka Island), Qingdao (Nagasaki Prefecture), Kuchino Island, Nakano Island, Suwanze Island, Shira Island, Akuseki Island, Chika Island, Okinawa Island, Uren Island (Kagoshima Prefecture), Sami Island, Aka Island, Otoshi Island, Kitadaito Island, Irabu Island, Iriomat Island and Hatruma Island (Okinawa Prefecture).
The Japanese weasel lives at altitudes from sea level to 336 meters. It has adapted to a wide variety of ecosystems in Japan and is commonly found in most habitats in Japan, including grasslands, forests, villages and suburbs, but does not usually occur in large cities and sometimes lives near human residential areas. But mainly in mountainous and f

Japanese weasel (scientific name: Mustela itatsi) is a species of weasel in the family Mustela, class Mammalia, with no subspecies.

Japanese weasel (Mustela itatsi) is a mammal in the family Mustela, once considered a subspecies of weasel. However, in 2011, studies of the skull morphology, body shape, coloration, and penis bones of the Japanese weasel documented interspecific and sexual differences between the Japanese weasel and the yellow weasel, as well as significant genetic differences, and all led to the Japanese weasel being recognized as a distinct species. In 2012, the Japanese weasel was upgraded from a subspecies to a separate species.

The wild population of the Japanese weasel is declining and they have disappeared from the lowlands of western Japan (Sasaki et al., 2014). The species is listed as "endangered" on the Red List in 10 prefectures in western Japan (2014). The Japanese weasel is not adapted to urban life and does not eat artificial foods. Through competition with introduced yellow weasels, the small female Japanese weasel may have difficulty reproducing in the lowlands of western Japan and has retreated to the hilly areas of Japan. Even without the introduction of potential competitors, the species may not be able to fully adapt to the various anthropogenic impacts in this part of Japan. The Japanese weasel and yellow weasel are phylogenetically close, which increases the possibility of their hybridization. However, no morphologically intermediate individuals were found among 15 yellow weasels monitored in northern Kyushu, Shikoku, and western Honshu in 2012, suggesting that hybridization may not pose a threat.

Listed on the 2016 IUCN Red List of Threatened Species, ver 3.1 - Near Threatened (NT).  

In Japan, female Japanese weasels are protected by law from hunting (2006).  

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