Not just birds and beetles: Iridescence found in unexpected animals

When people talk about iridescence, they usually think of butterflies, hummingbirds, or beetles. These animals shimmer when light hits them, creating colors that shift with each angle.

Mammals, by contrast, appear duller and more uniform. Their coats are typically brown, black, or grey, designed for camouflage and survival.

But recent research from Ghent University shows this picture is incomplete. Some mammals carry shimmering fur that rivals the beauty of birds and insects.

The discovery challenges long-standing assumptions and opens new questions about how common these hidden colors really are.

A surprising discovery

The story began in a museum, not in the wild. A researcher studying mammal specimens noticed an odd blue glint on the fur of a tropical vlei rat. That moment set everything in motion. Until then, golden moles were the only mammals widely recognized as iridescent.

These small African burrowers are known for their metallic, tinsel-like hairs. But the rat’s fur suggested something more was happening. If one overlooked species shimmered, perhaps others did too.

The observation was more than a curiosity. It challenged a simple claim in biology: that iridescence belonged almost entirely to creatures with scales or feathers. Mammals, it seemed, were the exception.

Searching the past

Instead of stopping at the rat, the researcher dug deeper. Old scientific reports contained scattered references to shiny fur in other mammals, some dating back to the late 1800s.

These notes were brief and often dismissed, treated as oddities rather than serious findings. For over a century, no one had followed them up. The new discovery gave reason to revisit those forgotten records.

By combining modern tools with these old clues, scientists could finally test whether mammals truly showed iridescence beyond golden moles. Museum collections, filled with preserved animals from around the world, provided the perfect opportunity.

Detecting iridescence in fur

The team examined specimens linked to historic mentions of iridescence. They also included related species to broaden the search. Using microscopes, they shone light at different angles across the hairs and measured how it reflected.

This simple test revealed the truth. Golden moles were not unique. Fourteen additional mammal species displayed iridescent coats. Ten were rodents.

Another was the giant otter shrew, a semiaquatic predator unrelated to either otters or shrews despite its name. For six of these animals, this was the first time iridescence had been scientifically recorded.

The discovery turned a narrow claim into a broader pattern. Iridescence in mammals, once thought to be nearly absent, now appeared in multiple groups.

How iridescent fur works

Understanding why the fur glowed required a closer look. Under high-powered microscopes, the hairs showed a special design. Normal mammal hairs are rough and uneven, made up of layers that scatter light. In contrast, iridescent hairs were smooth and compressed into parallel sheets.

Light striking these layers bent slightly at each surface. As the layers stacked, they bent light in multiple directions, creating interference patterns. The result was a rainbow shimmer, its colors changing as the viewing angle shifted.

The process resembled the one behind butterfly wings or beetle shells, though mammals achieved it through fur instead of scales.

Possible reasons for iridescence

Why would mammals develop such unusual hair? The answer is still uncertain. Many iridescent species are burrowers or swimmers. For animals living underground or in water, smooth hair could reduce dirt buildup or resist moisture. In that case, the shine would be a by-product, not an adaptation in itself.

Yet another explanation remains on the table. In birds, iridescence often serves as a communication tool, helping attract mates or signal dominance.

Mammals could use it the same way. If so, the shimmer would not be an accident but an important social feature. At present, scientists cannot say for sure. Both ideas remain possible, and both need further testing.

More iridescent species found

Evidence suggests the list of iridescent mammals is far from complete. In 2024, scientists described a new shrew from Indonesia with fur that appeared somewhat shiny.

With around 2,500 rodent species worldwide, and only a small portion studied under microscopes, the odds of finding more iridescent examples are high.

Each discovery adds weight to the idea that iridescence in mammals is not a rare exception. Instead, it may be a common but overlooked trait, hidden until light strikes at the right angle.

Biology remains full of surprises

The findings highlight the importance of close observation. For decades, scientists assumed mammal fur was plain because it usually looks that way under normal conditions. But assumptions can blind research.

Only when someone noticed a small flash of color did the story begin to change. Museum collections, often viewed as archives of the past, proved vital in rewriting the present understanding of mammal biology.

This work also shows how biology remains full of surprises. Even groups as familiar as rodents can carry traits we barely recognize. What seems ordinary may hold complexity beneath the surface.

Future research directions

Future studies will likely explore how iridescence affects animal behavior. Does it influence mating or social interactions? Does it offer camouflage under certain light conditions? Or is it simply a side effect of hair built for other environments?

Answering these questions will take fieldwork as well as lab analysis. The possibility of discovering many more iridescent mammals is exciting. Every new case adds to our picture of how structural colors evolve.

The research also reshapes our understanding of what mammals can look like. Far from being drab, some may shimmer like jewels under the right conditions.

Iridescent beauty in mammals

The discovery of iridescent fur in mammals changes a basic story about animal colors. It shows that beauty and complexity are not limited to insects, birds, or reptiles.

Mammals, too, can hide light-bending structures in their coats. These shimmering layers may serve survival, communication, or both.

What began with a single flash of blue on a museum specimen has opened a new chapter in biology. It proves once again that even in well-studied groups, nature still keeps secrets. Sometimes all it takes is the right angle of light to reveal them.

The study is published in the Journal of the Royal Society Interface.

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