Photograph by Analyn Cabras
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The newly discovered jewel weevil Metapocyrtus willietorresi (right) evolved to mimic the colors of another known species of jewel weevil, Pachyrhynchus reicherti.

Photograph by Analyn Cabras

Dazzling new mimic beetles found, may already be under threat

Jewel weevils are so good at deterring predators with their iridescent displays, other beetles are mimicking them, new research shows.

High up in the rainforests of the Philippines’ Mindanao Island, biologist Analyn Cabras spends her days handling tiny, iridescent insects with the delicacy of defusing a bomb.

Jewel weevils can sense the smallest vibrations, so that if a predator (or scientist) bumps the branch they’re standing on, the critters instinctively dive to the forest floor below. They then go belly up, their dark color blending into the ground.

“When we find a very rare species we try our best to be as cautious as possible, or else they will fall to the leaf litter, and once they do so, it will almost be impossible to find them,” says Cabras, a National Geographic Society Explorer and head researcher of the Coleoptera Research Center at the University of Mindanao.

While most people are familiar with the few weevil species that attack crops, the weevil family, Curculionidae, is actually one of the most diverse on Earth, with more than to 62,000 known species. (Read why insect populations are plummeting worldwide.)

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A new species of weevil called Metapocyrtus willietorresi was collected in the Philippines' Mount Apo Natural Park.

But many of the more than 400 species of Philippine jewel weevil have very small ranges, some as tiny as just one patch of forest.

Vexing as it is, Cabras has dedicated five years of her life looking for them—and that’s paid off with the recent discovery of two new jewel weevil species, with another seven in various stages of publication.

Weevil wonders

As their name suggests, jewel weevils are living gems. Their elytra, or wing covers, boast a variety of shimmery patterns etched in everything from brilliant turquoise and shiny gold to pale orange and the prettiest of pinks.

In fact, the weevils are so eye-catching, you’d think they’d be an easy mark for frogs, lizards, and birds. But these weevils want to be seen.

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“Their body is very strong. Even if you step on them, they won’t easily crush,” she says. “So the more colorful they are, it’s their way of advertising to predators that they’re not edible, and that if the predators actually eat them, they will have to suffer the consequences.” (Read about the giraffe weevil, whose males sport long necks.)

But what’s really interesting to Cabras is that several of the Philippine hard-shelled species seem to be evolving to look like each other. Even weirder, some of these weevils are closely related to each other, while others are not. Why?

Dazzling away danger

It’s all about educating the predators, says Cabras.

You see, warning markings only work if a predator recognizes those symbols as being dangerous, foul-tasting, or generally not worth its time. Over many generations, predators learn to stop eating anything that looks a certain way, which slowly coaxes multiple lineages of hard-shelled insect to look surprisingly similar. Scientists call this Mullerian mimicry.

But Cabras has discovered a second kind of mimicry at work, too, which she plans to describe in a future research paper. (Read more about the natural art of deception.)

“There is another type, called Batesian mimicry, wherein the jewel weevils are being mimicked by longhorn beetles,” she says. The difference here is that longhorn beetles have soft shells and are perfectly edible.

For these beetles, mimicry is a ruse. After all, why waste resources growing a protective shell when a few colorful patterns can have the same effect?

Poached jewels

“It’s interesting work,” says Robert Anderson, a weevil expert and research scientist at the Canadian Museum of Nature in Ottawa. “She is combining interesting aspects of the [weevils’] behavior and the morphology, which often you can’t do because a lot of times we just work with museum specimens,” he says.

Watch a Hercules Beetle Metamorphose Before Your Eyes May 11, 2018 - Watch this beetle go from larvae to giant. The Hercules beetle is one of the largest flying insects in the world. As beetle expert Brett Ratcliffe puts it, they “are basically the size of a Polish sausage.”

It’s also important that researchers like Cabras are out there documenting this biodiversity, as many of the beetles are being poached, killed and preserved, and then bought online by collectors.

For instance, online auction sites such as eBay sell hundreds if not thousands of specimens of Philippine weevils—all of them wild caught—which can fetch up to a few hundred dollars each, he says. (Learn about the illegal trade in tarantulas.)

So, in a twist, those same striking patterns that keep the weevils safe from predators make them appealing to collectors. And the longhorn beetle mimics? Their deception is so good, they end up getting illegally poached, too, says Cabras.

When you combine poaching with the rate at which the country is logging, mining, and converting forests into plantations, Cabras says the outlook is worrisome for some of the rarest species, like Metapocyrtus willietorresi and Pachyrhynchus naokii.

“Some of them will probably be gone in the next five to ten years,” she says, “if we don’t do anything about it.”