Mustela itatsiJapanese weasel

Geographic Range

Mustela itatsi was historically native to three of Japan’s four larger islands: Honshu, Kyushu, and Shikoku. Over the past century, they have been introduced to most other Japanese islands for the purpose of rodent control. The current range includes Hokkaido and the majority of the Ryukyu Islands. ("Mustela itatsi", 2012; Abramov and Wozencraft, 2012)


Japanese weasels are found in a wide variety of Japanese ecosystems, but primarily mountainous and forested areas near moving water. Most hunting is done along rivers, but these weasels occasionally venture into grasslands or suburban areas. ("Mustela itatsi", 2012; Abramov and Wozencraft, 2012; Higash, 1988; Hooper, 2003)

In winter, these slim-bodied weasels spend most of their time beneath the snow chasing small rodents through a maze of tunnels. After catching and eating prey, Japanese weasels often enjoy the warmth of the quarry’s nest after eating. (King, et al., 2007)

  • Aquatic Biomes
  • rivers and streams

Physical Description

As with all weasels, Mustela itatsi has a long, slender body with short legs and a stout neck and head. Japanese weasels are larger weasels; adult males have a body and tail length between 45 and 52 cm and an average weight of 400 g. Females are generally smaller. Their coats are usually golden-orange with lighter coloring on the belly, and darker markings near the face. In response to the shortening of daylight, weasels stop producing melanin and their coat turns white and becomes thicker in preparation for winter. ("Mustela itatsi", 2012; Hooper, 2003)

Although their body is well-suited for running down tunnels and into tight spaces, it is not very efficient for retaining heat and energy. Weasels must continually search for food to overcome this disadvantage. (King, et al., 2007)

  • Sexual Dimorphism
  • male larger
  • Range mass
    150 to 450 g
    5.29 to 15.86 oz
  • Range length
    40 to 52 cm
    15.75 to 20.47 in


The mating process for M. itatsi starts off with the male seeking out females by smelling and analyzing their scent marks. Once he tracks down a female, a mix of play and biting occurs from a few hours to several days. When the female is ready, she allows the male to bite her around the neck and pin her down. Copulation is brief, but may take place multiple times for each couple. Soon after, they go their own ways and likely never see each other again. (King, et al., 2007)

Mating occurs from early May to late June. However, if there is a particular abundance of food, mating may occur until August, producing a second litter during the season. After mating, gestation takes about 30 days. The number of kits varies from 2 to 12, but is usually 5 or 6. It takes 8 weeks to fully be weaned and independent. Japanese weasels are sexually mature at one year old. (King, et al., 2007)

  • Breeding interval
    Japanese weasels generally breed once yearly, although second litters may occur in years with abundant food resources.
  • Breeding season
    Mating occurs from early May to late June or into August.
  • Range number of offspring
    2 to 12
  • Average number of offspring
  • Range gestation period
    26 to 29 days
  • Range weaning age
    8 to 9 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Females are solely responsible for parenting in Mustela itatsi, from conception to independence. Males leave females once mating is complete. Mothers will build nests in abandoned holes, cavities, or logs using grasses, feathers, and animal fur. Once the kits are born, their mother feeds them milk until their canines develop fully and they can consume flesh. Once old enough to move about, young weasels practice valuable hunting skills through play behavior. Soon after, they tag along with their mother to go hunting. Once they can hunt on their own, they’re considered independent and leave their mothers protection to find their own territory. (King, et al., 2007)

  • Parental Investment
  • altricial
  • female parental care
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


Lifespan in Mustela itatsi is similar to other members of the genus Mustela. As a close comparison, M. sibirica has lived up to 8 years in captivity. Longevity in the wild is highly dependent on food availability. Average lifespan is likely to be 2 to 3 years.

  • Typical lifespan
    Status: wild
    5 (high) years
  • Average lifespan
    Status: wild
    2 years


Japanese weasels are solitary animals, with the exception of mating courtships, and mothers with young. They are very territorial and will aggressively defend their home range, especially dominant males. All weasels present an aggressive defense against threating animals, even against much larger species. Also, when cornered or very frightened, weasels release a potent dose of musk to deter attackers. (King, et al., 2007)

Japanese weasels are also expert hunters, chasing down prey by any means, including running down tunnels, climbing trees, or swimming. Anywhere prey can go, the weasel can follow. Very high hunting success is achieved through these abilities. They are both diurnal and nocturnal. (King, et al., 2007)

Home Range

There is no information on home range size in Japanese weasels.

Communication and Perception

In order to communicate with other weasels or other animals, Japanese weasels use two main modes of communication: chemical and acoustic. Individuals secrete a substance known as musk from their characteristic anal glands, used in chemical communication. Weasels are territorial and establish territorial boundaries by rubbing their glands over obstacles such as branches and stones. Scent marks communicate gender, age, social status, health, and breeding condition. (King, et al., 2007)

Japanese weasels emit a wide range of calls and sounds. Primary calls include a low intensity trill, chirp, bark, screech, and hiss. Trilling generally signifies comfort when a mother is with her young. Chirping is another content call when danger is not present. Barking, screeching, and hissing all indicate imminent danger. (King, et al., 2007)

Food Habits

Since they are able to live in a wide range of Japanese habitats, these weasels have a wide range of prey options. They prefer to catch live prey such as rodents, amphibians, reptiles, birds, and some crustaceans. These weasels are also nest raiders, and enjoy bird eggs or young chicks. A common prey bird species is the Japanese bush warbler (Cettia diphone). When prey is scarce they resort to eating various fruits and berries. When food is abundant it is common for weasels to cache food items for later consumption. ("Mustela itatsi", 2012; Abramov and Wozencraft, 2012; Hamao, et al., 2009; Hooper, 2003; Kaneko, et al., 2009; Keishi, et al., 2002; King, et al., 2007)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • amphibians
  • reptiles
  • fish
  • eggs
  • insects
  • terrestrial worms
  • aquatic crustaceans
  • Plant Foods
  • fruit


Despite their carnivorous lifestyle, the small body size of Japanese weasels make them a target to some large predators, mainly birds of prey. Their musky scent makes them less palatable to mammalian predators. (King, et al., 2007)

Ecosystem Roles

Japanese weasels help in controlling rodent and other small animal populations. There is also evidence that they are effective at spreading seeds through feces. (Sato, et al., 2006; Tsuji, et al., 2011)

  • Ecosystem Impact
  • disperses seeds
Commensal/Parasitic Species
  • Paragonimus ohirai
  • Gnathostoma nipponicum

Economic Importance for Humans: Positive

In the past century Japanese weasels have been introduced to many of Japan's small islands to kill rats that were damaging crops. Along with the use of some rodenticide, the weasels helped reduce rat populations. (Uchida, 1968)

Japanese weasels are also trapped and used in the fur industry.

  • Positive Impacts
  • body parts are source of valuable material
  • controls pest population

Economic Importance for Humans: Negative

Japanese weasels also occasionally prey on domestic birds, such as chickens and ducks.

Conservation Status

Although their populations are in slight decline, Japanese weasels are listed on the IUCN Red List as Least Concern because of their widespread population across Japan. The primary threat to Japanese weasels is habitat loss due to residential and commercial development. (Abramov and Wozencraft, 2012)

Other Comments

A common misunderstanding among people is that Japanese weasels (Mustela itatsi) and Siberian weasels (Mustela sibirica) are the same species with different common names. Recent studies have proven this to be false. These two species are distinguished from one another by specific body/tail ratios and unique genotypes. (Masuda, et al., 2012)


Eric VanNatta (author), University of Wisconsin-Stevens Point, Christopher Yahnke (editor), University of Wisconsin-Stevens Point, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


uses sound to communicate


living in landscapes dominated by human agriculture.


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


active at dawn and dusk

  1. active during the day, 2. lasting for one day.

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

island endemic

animals that live only on an island or set of islands.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


having more than one female as a mate at one time


Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


lives alone

stores or caches food

places a food item in a special place to be eaten later. Also called "hoarding"


living in residential areas on the outskirts of large cities or towns.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.


A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


2012. "Mustela itatsi" (On-line). Encyclopedia of Life. Accessed August 17, 2012 at

Abramov, A., C. Wozencraft. 2012. "Mustela itatsi" (On-line). ICUN Red List of Threatened Species. Accessed August 10, 2012 at

Hamao, S., K. Nishimatsu, T. Kamito. 2009. Predation of Bird Nests by Introduced Japanese Weasel Mustela itatsi on an Island. Ornithological Science, 8/2: 139-146. Accessed August 18, 2012 at

Higash, H. 1988. "Ecological study of Japanese Weasel (Mustela itatsi) in Tamagawa River by radio-telemetry method" (On-line). The Tokyu Foundation for Better Environment. Accessed August 18, 2012 at多摩川河川敷におけるイタチの生息状況の把握な?lang=en.

Hooper, R. 2003. "Animal Tracker Japanese Weasel" (On-line). The Japan Times Online. Accessed August 10, 2012 at

Kaneko, Y., M. Shibuya, N. Yamaguchi, T. Fujii, T. Okumura, K. Matsubayashi, Y. Hioki. 2009. Diet of Japanese Weasels (Mustela itatsi) in a Sub-Urban Landscape: Implications for Year-Round Persistence of Local Populations. Mammal Study, 34/2: 97-105. Accessed August 10, 2012 at

Keishi, S., O. Go, S. Takeshi, N. Yasuhiko, T. Kojun, K. Yoshitsugu. 2002. Food Habits of Introduced Japanese Weasels(Mustela itatsi) and Impacts on Native Species on Zamami Island.. Mammalian Science, 42/2: 153-160.

King, C., R. Powell, C. Powell. 2007. The Natural History of Weasels and Stoats. Oxford, New York: Oxford University Press.

Masuda, R., N. Kurose, S. Watanabe, A. Abramov. 2012. Molecular phylogeography of the Japanese weasel, Mustela itatsi (Carnivora: Mustelidae), endemic to the Japanese islands, revealed by mitochondrial DNA analysis. Biological Journal of the Linnean Society, 29/5: 1095. Accessed August 18, 2012 at

Sato, H., K. Suzuki, A. Osanai, M. Aoki. 2006. Paragonimus westermani and some rare intestinal trematodes recovered from raccoon dogs (Nyctereutes procyonoides viverrinus) introduced recently on Yakushima Island, Japan.. The Journal of Veterinary Medical Science, 68/7: 681-687.

Tsuji, Y., T. Tatewaki, E. Kanda. 2011. Endozoochorous seed dispersal by sympatric mustelids, Martes melampus and Mustela itatsi, in western Tokyo, central Japan. Mammalian Biology, 76/5: 628-6333. Accessed August 10, 2012 at

Uchida, T. 1968. Observations on the Efficiency of the Japanese Weasel, Mustela sibirica itatsi Temminck & Schlegel, as a Rat-Control Agent in the Ryukyus. Bulletin of the World Health Organization, 39/6: 980. Accessed August 10, 2012 at