Stoat or weasel? How to tell the difference

Have you been lucky enough to encounter a stoat or weasel on a woodland walk?

These mini predators are hard to spot and most sightings are no more than a fleeting glimpse. With the two species looking very similar, this can make it tricky to tell them apart. Here’s a handy guide to help you out.

The trick is in the tail 

The easiest and most reliable way to tell a stoat (Mustela erminea) from a weasel (Mustela nivalis) is the tail. A stoat’s tail is around half the length of its body and ends in a bushy black tip. A weasel’s tail is short and stubby by comparison and solely brown in colour.

Other subtle differences to look out for include:

• Size - Stoats are larger than weasels with a typical whole body length of 30-40cm, compared to the weasel’s 20-27cm.
• Movement - Stoats have a characteristic bounding gait with an arched back. The movement of weasels is often quicker and flatter to the ground.
• Colour - Stoats sometimes turn white in winter, especially in Scotland. UK weasels stay brown all year round.

Where to see stoats and weasels

Stoats and weasels are found throughout mainland Britain. However, Ireland is solely home to stoats where, just to confuse matters, it is often called a weasel.

Both species live in woodland and most other habitats as long as there is sufficient cover to hide in and plenty of rabbits, rodents and birds to eat.

A preference for hunting rabbits means you are perhaps more likely to spot a stoat in the open. But, like weasels, they spend most of their time under cover to avoid larger predators such as foxes and birds of prey.

The rest of the mustelid family

Closely related, stoats and weasels are members of the mustelid family. Here is a brief guide to identifying the other mustelids found in the UK:

Otter (Lutra lutra) & mink (Neovison vison)

Two mustelids people sometimes confuse are the otter and mink. Both species are semi-aquatic, spending much of their time in water. However, it’s easy to tell the difference when you know what to look for:

• Size: Otters are much larger, with a typical whole body length of more than one metre. This is around twice the length of a mink - and an otter can be ten times heavier.
• Colour: Otters have brown fur, while mink are notably darker, appearing almost black.
• Tail: An otter’s tail is long and thick, while a mink’s tail is bushy and smaller.

Mink are not native to the UK. A wild population became established in the 20th century following escapes and releases from fur farms. This has had a damaging impact on some native species, particularly the water vole.

However, mink are now thought to be in decline. This is partly due to the ongoing recovery of the otter population. Otter numbers are estimated to have grown by 50% since 1995 thanks to legal protection and reduced river pollution. With similar habitat preferences, it’s thought the larger otter out-competes the smaller mink.

Polecat (Mustela putorius)

Like the otter, legal protection has helped polecat numbers grow in recent decades. The species was hunted to extinction everywhere bar mid-Wales by the end of the 19th century, but has steadily been reclaiming its former haunts.

Key identification features include:

• Similar size to mink, but can be distinguished by ‘bandit mask’ facial markings.
• Fur colour is a mixture of buff and dark brown.
• Most common in Wales and western England, but spreading across mainland UK.
• Nocturnal and rarely seen in the day.
• Does not occur in Ireland.

Did you know the polecat is the wild ancestor of the domestic ferret and will hybridise with escaped ferrets? Feral ferrets are variable in appearance and can range from near white to being much like polecats. Hybrids are difficult to tell from true polecats without close observation.

Badger (Meles meles)

Badgers are unmistakable, but you may not have realised they are also mustelids. The species is the largest member of the family in the UK. A male badger may weigh up to 17kg; that’s as much as 250 female weasels!

Pine marten (Martes martes)

Our final mustelid is the pine marten. Key identification features include:

• Around the size of a small cat, with brown fur and a creamy-white throat patch.
• Long bushy tail.
• The mustelid most likely to be seen in trees.

Pine martens had disappeared from most of the UK by the 20th century due to hunting and destruction of their woodland habitat. As a result, the majority of the population is now found only in Scotland. Thankfully numbers are increasing here, but the species’ situation in England and Wales remains precarious. Only a handful of isolated populations are left in both countries.