Otter shrews explained: Not otters, not shrews, not quite tenrecs

Animal names can be misleading. The “otter shrews” of Africa are a perfect example. At first glance, these semi-aquatic mammals look like miniature otters. Their pointed snouts suggest a shrew, and for a long time taxonomists even thought they might be related to the Madagascan tenrecs. But in reality, otter shrews are none of these things. They are a small, unique branch of African mammals with their own evolutionary story.

First Impressions: Why the Name?

Otter shrews live in streams and rivers across central and western Africa. Their sleek bodies, dense fur, and strong tails make them superb swimmers, much like true otters. Yet they are far smaller; most species are only 25–35 cm long, including the tail. Their long, sensitive snouts twitch constantly, reminding observers of shrews. The mix of these traits earned them their confusing common name.

A Taxonomic Puzzle

For much of the 19th and 20th centuries, zoologists debated where otter shrews fit. Because they share many superficial features with shrews, they were first placed in the order Insectivora, a catch-all group that also held hedgehogs, moles, and tenrecs. Later, some researchers suggested that otter shrews might actually be a type of tenrec, since tenrecs on Madagascar also show a remarkable diversity of body forms and some are semi-aquatic.

It wasn’t until the advent of molecular genetics that the picture became clearer. DNA studies revealed that otter shrews belong to their own family, the Potamogalidae, within the order Afrosoricida. This is the same order that contains tenrecs, which explains the earlier confusion. However, otter shrews split from the lineage that led to modern tenrecs tens of millions of years ago, making them close cousins rather than members of the same family.

Not Otters, Not Shrews

So what exactly are they?

• Not otters: Otters are carnivores (family Mustelidae), closely related to weasels, stoats, and badgers. Otter shrews only resemble them in body shape and swimming habits, the result of convergent evolution — when unrelated animals evolve similar traits to adapt to similar lifestyles.
• Not shrews: True shrews belong to the order Eulipotyphla (together with hedgehogs and moles). Otter shrews only look shrew-like because of their pointed faces and small size.
• Not quite tenrecs: They were once lumped in with tenrecs, but genetic evidence shows they diverged long ago. Today they are recognised as a distinct family within Afrosoricida, alongside but separate from Tenrecidae.

Life in Water

Otter shrews are adapted for an aquatic lifestyle. Their dense, waterproof fur keeps them warm. Their tails are flattened side-to-side to help with propulsion, and their hind feet are partially webbed. They hunt underwater using their sensitive snouts to detect movement, feeding mainly on insects, crustaceans, and small fish.

They are nocturnal and secretive, spending the day in burrows near riverbanks and emerging at night to swim and forage. Because they are elusive and inhabit remote waterways, otter shrews remain poorly studied, and much about their behaviour is still unknown.

Conservation Concerns

As with many small mammals, otter shrews face growing threats. Deforestation, agriculture, and damming of rivers reduce the clean waterways they depend on. Pollution and human disturbance may also shrink their range. Their secretive nature makes population monitoring difficult, meaning declines could go unnoticed. Protecting river ecosystems in central and western Africa is vital not only for otter shrews but also for countless other freshwater species.

Why They Matter

Otter shrews are a reminder that Africa’s mammal diversity extends far beyond the famous elephants, lions, and gorillas. They are living examples of evolution’s creativity — animals that look like one thing but are, genetically, something entirely different. By studying them, scientists gain insight into the early evolution of Afrosoricida, the same order that includes Madagascar’s tenrecs. And by protecting their habitats, we safeguard yet another unique thread in the fabric of global biodiversity.

In Summary

The otter shrew is not an otter, not a shrew, and not quite a tenrec. It is its own creature, adapted to life in Africa’s rivers, and part of a fascinating branch of mammals that has often been overlooked. Their story is a lesson in the dangers of judging animals by appearance alone and in the importance of looking deeper to understand where each species truly belongs.