Jewel beetles bend light to make themselves invisible to predators

January 24, 2020, 2:13 p.m.
A  rainbow jewel beetle sitting in a leaf.
Photo: Mark Brandon/Shutterstock

We see you, little jewel beetle.

But apparently, predators have a hard time distinguishing that stunningly iridescent shell from its natural surroundings.

That may sound counterintuitive to the rules of camouflage. After all, insects and animals that rely on the evolutionary technique typically aim to blend in or at least color-match with the background.

But new research from the University of Bristol suggests the jewel beetle's strategy of standing out is at least as effective as blending in. In fact, the beetle, along with other bright and shiny creatures, may even get a boost when perched on glossy surfaces.

A paper, published this week in the journal Current Biology, builds on the work of the so-called father of camouflage, Abbott Handerson Thayer. An early 20th century artist and naturalist, Thayer noted that iridescent species alternate hues based on the perspective they're being viewed from.

"The idea of 'iridescence as camouflage' is over 100 years old, but our study is the first to show that these early ignored or rejected ideas that 'changeable or metallic colors are among the strongest factors in animals' concealment' have traction," notes the study's lead author, ecologist Karin Kjernsmo, in a press release. "Both birds and humans really do have difficulty spotting iridescent objects in a natural, complex, forest environment."

A close-up of a green beetle's wing. Colors can change dramatically when they're bounced off the lattice-like structures of a beetle's wings. (Photo: aodaodaodaod/Shutterstock)

For most bugs and animals, a bright and brilliant appearance can be a catch-22. While being all shimmery can do wonders for attracting mates, it's also a siren call for hungry predators. Most creatures aim for the right balance between low-key and mate-magnetizing beauty. But sometimes, when looking for love, you have to put yourself out there.

And jewel beetles make absolutely no compromises.

But how does a creature so stunningly technicolor survive even a day in a big, hungry natural world? And why are there so many other iridescent creatures, from birds to snakes, that don't even bother trying to blend in? The study suggests we should look at iridescent as a different kind of camouflage. While geckos become bark-like and jaguars ghost into foliage, jewel beetles actually count on their eye-popping shell to baffle predators that come sniffing around.

That's because the colors we see don't originate from the beetle's pigments. Instead, its wings form lattices that break up light waves and push them up against each other. The technique, called diffraction, makes light — and hence color — visible from certain directions and angles. Some light rays are blocked; others are allowed through.

Researchers compare the effect to a holograph you might see on a baseball card or the shimmer of an abalone shell. It's dazzling from one angle, but shift the card slightly and it disappears.

An abalone, or mother of pearl, on the beach. The abalone shell, or mother of pearl, uses a similar lattice-like structure to diffract light rays. (Photo: Lost Mountain Studio/Shutterstock)

"Although an iridescent insect might be easy to spot in a well-lit museum case, these spectacular colors may not shine as brightly in the dappled light of a natural environment, and so an iridescent beetle on a shiny leaf could be much more difficult to detect," Kjernsmo explains. "If iridescence is to work as a form of protective coloration, it needs to work against birds, because birds are likely to be the most important predators of many iridescent insects."

Indeed, it may even work better than traditional camouflage.

In lab tests, the research team pitted iridescent wing cases against dull-colored wing cases. Surprisingly, they found those bright wings were superior at flying under the radar of both birds and humans. They even proved less detectable than wings that were leaf-colored green.

What's more, when placed on a glossy leaf, the jewel beetles were even harder to detect. Dubbing it "dynamic disruptive camouflage," researchers suggest the combination of gloss and iridescence creates an illusion of inconsistent features and depth, further baffling predators.

And they suspect this kind of wizardry is common among all iridescent species.

"We don't for a minute imagine that the effect is something unique to jewel beetles; indeed, we'd be disappointed if it was," Kjernsmo adds. "If we found that these beetles could be concealed by their colors, it increases the chances that many iridescent species could be using their colors this way."