A weasel native to Honshu, Shikoku, Kyushu and nearby islands, with an elongated body, short legs and a dark mark from forehead to nose.
Adult males are larger than females. A dark forehead-to-nose mark contrasts with the surrounding coat.
Japanese weasels eat fruit as well as small animals. At Watarase-yusuichi wetland, fruit seeds occurred in 80% of scats collected in summer, alongside frequent beetle remains. Seeds also appeared in winter, together with leaves and fragments of plant stems or roots. Seasonal plant foods form part of this waterside carnivore’s meals.
A study published in 2026 examined 103 scats collected along embankments, maintenance roads and other paths from September 2024 to August 2025. Researchers washed the samples and examined remaining hairs, bones, insect fragments and seeds under magnification. Of 20 summer scats, 16 contained fruit seeds and 14 contained beetles. Of 22 spring scats, eight contained fish and seven contained mammal remains. While seeds and insects stood out in summer samples, aquatic fish and terrestrial mammals also appeared in the traces of spring meals. The records revealed varied food use within a wetland mosaic of reed beds, ponds and channels.
An extinction-risk assessment has not been added yet.
Fukuoka Prefecture’s 2024 Red Data Book reports that Japanese weasels have disappeared from lowlands following development and other changes, while introduced Siberian weasels have spread. Siberian weasels also occur around settlements and cultivated areas in the mountains. Separately, the 2026 Watarase-yusuichi diet study recommends maintaining diverse wetland habitats, including reed beds, levees and adjacent terrestrial vegetation. It also warns that management benefiting competing introduced carnivores could disadvantage Japanese weasels. These are proposals that consider both habitat diversity and the animals sharing it.