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What the sources say

Least WeaselMustela nivalis

Every figure, record and mechanism on the Least Weasel profile was written from a source, and this is the working table behind it: 65 claims checked word for word against these sources. The left column is what the page says. The right column is the source's own words, copied, not paraphrased; a ... marks a cut and[brackets] an insertion. Open any source and check it yourself.

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Source
01

Animal Diversity Web, University of Michigan

Mustela nivalis (least weasel). Animal Diversity Web, University of Michigan.

The page saysWeighing as little as 30 grams
The source saysRange mass 30 to 100 gNote: tagline; prey and weight clauses are the next two claims
The page sayskills prey larger than itself
The source saysweasels frequently kill prey larger than themselves
The page sayscan eat over half its own body weight in a day
The source saysWeasels can consume over 50% of their body weight every day
The page saysGrassland, forest, tundra and farmland across the Northern Hemisphere
The source saysLeast weasels are widespread and abundant throughout the Northern HemisphereNote: stats.habitat
The page saysGrassland, forest, tundra and farmland
The source saysThey are found in prairie grasslands, coniferous and deciduous forests, open tundra, bushy taigaNote: stats.habitat
The page saysfarmland
The source sayssuch as those found in prairie habitats or on agricultural landsNote: stats.habitat
The page saysVoles and mice
The source saysField voles , wood mice , and bank voles constitute much of a least weasel’s diet in more southern populationsNote: stats.diet
The page sayslemmings in the Arctic
The source saysRodents, especially collared lemmings in the northern arctic regions, are vitally importantNote: stats.diet
The page saysbirds' eggs
The source saysleast weasels will also feed upon birds’ eggs, lizards, amphibians, small fish, and invertebratesNote: stats.diet
The page saysKills prey larger than itself
The source saysweasels frequently kill prey larger than themselvesNote: stats.superpower; weight clause is the claim above
The page sayslong, tubular body and short limbs
The source saysa typical mustelid body shape: a long, tubular body, with short limbs
The page saysit moves easily through leaf litter, underground tunnels and subnivean tunnels, which are the ones beneath the snow
The source saysmaneuvering easily through both leaf litter, subterranean, and subnivean tunnelsNote: 'beneath the snow' is the definition of subnivean (term gloss, not a source claim)
The page saysIt does not dig its own den. It uses dens abandoned by its prey or other burrowing animals.
The source saysdo not burrow or dig dens; they use the abandoned dens from prey or other fossorial species
The page saysAcross its range a least weasel weighs 30 to 100 grams
The source saysRange mass 30 to 100 g
The page saysTiny: 30 to 100 grams
The source saysRange mass 30 to 100 gNote: FAQ 1; the length clause is the next claim
The page saysmeasures 165 to 217 millimetres including the tail
The source saysRange length 165 to 217 mmNote: ADW's text says total lengths include the tail
The page saysincluding the tail
The source sayscan reach total lengths (including the tail) over 217 mm
The page saysmales are the bigger sex
The source saysSexual Dimorphism male larger
The page saysIndividuals from warmer climates tend to be bigger
The source saysindividuals from warmer climates tend to have larger body sizes and masses than those from colder climates
The page sayspopulations in North Africa can weigh over 70 grams
The source sayssuch as individuals from populations of North Africa, which can weigh over 70 grams
The page saysNorth American weasels average about 45 grams and about 190 millimetres
The source saysThe smallest weasels are in North American populations and weigh, on average about 45 grams, and average about 190 mm in length (including the tail)
The page saysnative from Alaska through Canada and the northern United States, and in Europe outside Ireland
The source saysnative to North America, from Alaska, south throughout Canada and the northern United States, and Europe (excluding Ireland, Greenland, and Iceland)
The page saysIn northern populations the coat turns pure white in winter, but it always lacks the black tail tip that stoats and long-tailed weasels carry.
The source saysThe pelage color changes seasonally in northern populations, but not in more southerly populations. In the winter, the coat is pure white, but always lacking the black tail tip found in two similar species
The page saysstores little fat, has very high metabolic demands
The source saysBecause least weasels are so small, have limited abilities in storing fat, and have such high metabolic demands
The page saysmust eat very regularly to avoid starving
The source saysLeast weasels must eat very regularly to avoid starvation and death
The page saysmore than half its body weight in food every day, and more still in winter
The source saysWeasels can consume over 50% of their body weight every day and even more so in the winter months.
The page saysit is often out foraging day or night
The source saysare often found foraging at all hours, day or night
The page saysField voles, wood mice and bank voles make up much of the diet in southern populations, and when rodents are plentiful they can be almost 100 percent of it.
The source saysalmost 100 percent of a weasel's diet is made up of rodents if they are abundant
The page saysIn the Arctic, collared lemmings are vitally important for breeding success.
The source saysRodents, especially collared lemmings in the northern arctic regions, are vitally important for weasel reproductive success.
The page saysWhen rodents are scarce, a weasel will switch to birds' eggs, lizards, amphibians, small fish and invertebrates, and it will not turn down carrion.
The source saysWhen rodents are scarce, least weasels will also feed upon birds’ eggs, lizards, amphibians, small fish, and invertebrates.
The page saysit will not turn down carrion
The source sayswill not overlook an easy meal, such as carrion
The page saysA weasel often takes down animals bigger than itself, but each meal is only a few grams of meat.
The source saysweasels frequently kill prey larger than themselves, yet they only eat a few grams of meat per meal
The page saysThe leftovers are cached, hidden near the den entrance for later.
The source saysCaches are concealed around the den entrance
The page saysKits are born hairless and helpless.
The source saysKits are born hairless and helpless
The page saysGestation lasts about a month.
The source saysGestation lasts approximately one month
The page saysBy about 47 days they can kill prey for themselves.
The source saysAt about 47 days, the kits are able to kill prey for themselves
The page saysKilling is an innate behaviour: captive kits with no experience of prey still kill it, though kits that stay with their mother have higher success rates.
The source sayskilling is an innate behavior and kits in captivity kill prey with no previous experience or exposure to prey; however, kits that remain with their mother and gain practical hunting experience have higher success rates
The page saysa litter can reach 15 kits and a female can have up to three litters in a year
The source saysup to 15 offspring can be born, and up to three litters per year can occur
The page saysWhen prey is plentiful, as when Arctic lemming numbers boom
The source saysDuring years of high prey abundance and in areas such as the Arctic, where lemming populations can reach astronomical numbers
The page saysOwls, falcons, eagles and hawks typically prey on adults
The source saysadults are typically preyed upon by owls, such as tawny owls , and other birds of prey, such as falcons, eagles, and hawksNote: foxes and snakes are juvenile predators in ADW; larger weasels follows
The page sayssnakes and foxes often take the young
The source saysJuvenile mortality is common from predation by snakes and foxes
The page sayslarger weasels such as the stoat may also eat least weasels
The source saysLeast weasels may also be preyed upon by other larger weasel species, such as ermines and long-tailed weasels
The page sayscamouflage, hiding, biting and noise
The source saysLeast weasels can counteract predation events by using their camouflaged pelage to blend in with substrate and aggressive behavior, such as vocalizations and biting, and by hiding in shelters
The page sayswhen cornered or startled it can discharge a foul-smelling fluid from its anal glands
The source saysWhen cornered or startled, anal gland secretions can be discharged, which release a foul-smelling fluid that can deter an antagonist.
The page saysweasel war dance, a series of leaps and twists with an arched back and stiff limbs, often with bark-like calls
The source says“weasel war dance”, a colloquial term used to describe a intermittent series of leaps and twists, often accompanied by bark-like vocalizations, stiff limbs, an arched back
The page saysIt is thought to perplex prey, but that is one hypothesis
The source saysOne hypothesis is that the war dance is thought to perplex prey and to give the weasel a hunting advantage
The page saysthere is no solid scientific evidence explaining it, and weasels have been seen dancing without an audience
The source saysat this time, there is no solid scientific evidence explaining this behavior ... there are cases where the weasels perform this “dance” lacking an audience
The page says165 to 217 millimetres from nose to tail tip
The source saysRange length 165 to 217 mmNote: FAQ 1; ADW's total lengths include the tail
The page saysa least weasel in winter white always lacks the stoat's black tail tip
The source saysIn the winter, the coat is pure white, but always lacking the black tail tip found in two similar species
The page saysBuilt for Tunnels
The source saysmaneuvering easily through both leaf litter, subterranean, and subnivean tunnels
The page saysEating Half Its Weight
The source saysWeasels can consume over 50% of their body weight every day
The page saysMusk and the War Dance
The source says“weasel war dance”, a colloquial termNote: heading; musk: ADW 'anal glands, or musk glands', claimed in the body
The page saysNorth American animals are the smallest, averaging about 45 grams
The source saysThe smallest weasels are in North American populations and weigh, on average about 45 grams
The page saysThe menu is mostly rodents.
The source saysLeast weasels are highly specialized rodent predators and as such, they rely heavily upon rodent species for food.
The page saysBorn Ready
The source sayskilling is an innate behavior
The page saysPrey numbers have a dramatic effect on how many litters and young a female has.
The source saysPrey density has a dramatic effect on the number of litters per year and the number of young per litter.
The page saysA weasel this size is prey for plenty of animals.
The source saysKnown Predators red foxes ( Vulpes vulpes ) grey foxes
The page saysThe stoat is a larger weasel species that can prey on least weasels
The source saysLeast weasels may also be preyed upon by other larger weasel species, such as ermines and long-tailed weaselsNote: FAQ 2; ermine is the stoat (ADW: 'ermines, or stoats')
The page saysThe least weasel's war dance is a series of leaps and twists with an arched back and stiff limbs, often with bark-like calls
The source says“weasel war dance”, a colloquial term used to describe a intermittent series of leaps and twists, often accompanied by bark-like vocalizations, stiff limbs, an arched backNote: vibe.reason
The page saystags: agile
The source saysmaneuvering easily through both leaf litter, subterranean, and subnivean tunnelsNote: task #1246; Agile tag kept: quick manoeuvring over tangled ground and through tunnels; the war dance in the body is the other half.

Source
02

AnAge: The Animal Ageing and Longevity Database

Mustela nivalis. AnAge: The Animal Ageing and Longevity Database.

The page saysIn captivity the oldest recorded least weasel reached 9.1 years.
The source saysMaximum longevity 9.1 years (captivity)
The page saysThe AnAge database gives a maximum longevity of 9.1 years in captivity. That is a captive figure, not a wild one.
The source saysMaximum longevity 9.1 years (captivity)
The page saysweightKg: 0.0469
The source saysAdult weight 46.9 gNote: task #1246; AnAge adult weight; Micro class (under 100 g). Name guess would have been Medium.

Source
03

Abramov 2025

Abramov (2025). Mustela nivalis. The IUCN Red List of Threatened Species 2025: e.T70207409A215863028.

The page saysLeast Concern
The source saysIUCN Red List category: Least Concern (LC).Note: stats.conservationStatus; category read through GBIF's copy of the Red List (assessment DOI cited)
The page saysThe International Union for Conservation of Nature rates the species Least Concern.
The source saysIUCN Red List category: Least Concern (LC).

How the table was made: a writer drafted the profile from these sources and logged each claim with its quote, a reviewer with nothing but this table checked every sentence said no more than its quote, and a script confirmed each quote appears word for word in the source. The method is in the site'sAbout page.