The Strange Saga of the Harlequin Beetle and the Pseudoscorpion

A comically long-legged harlequin beetle. To its right is the miniscule pseudoscorpion, which spends most of its time mating on the beetle's back. One might argue, then, that this baby does indeed have back.

Say what you will about the calamity that is air travel, but at least the planes have roofs. And at least the other passengers aren’t trying to throw you out mid-air because of said problem with the roof. At least no one is having sex all around you, and at least when you land, your plane doesn’t up and start getting busy with another plane.

Welcome to Harlequin Beetle Airlines, where the skies aren’t so much friendly as they are sexually awkward. The passengers are teeny-tiny arachnids called pseudoscorpions, which crawl under a harlequin beetle’s wings and latch on with their claws and strap in with silken seat belts. The dominant males among the pseudos shove other males off and get busy with a harem of females right on the back of the harlequin—itself a bizarre creature whose males tread on wildly elongated front legs.

It’s hard to imagine an odder couple out there. So this, ladies and gentlemen, is an Absurd Creature of the Week twofer: the strange saga of the harlequin beetle and the pseudoscorpion.

Arachnids do a lot of things really well (like straight-up murder). But one thing they can’t do is fly to new resources. A lot of spiders will do something called ballooning, simply letting out a line of silk for the wind to pick up and drag it into the sky, but pseudos live in the rainforests of South and Central America, where foliage is too dense for wind to penetrate. Plus, they only hang out in dead ficus trees. So they need some way to get to the next fallen plant.

A closer shot of the pseudoscorpion on a lovely backdrop of harlequin beetle.

Luckily the harlequin beetle also loves itself a dead ficus tree, specifically as a place to lay its eggs. When these hatch, the resulting larvae bore into the wood and begin pupating. Meanwhile, pseudos in the tree are milling about hunting.

“They tend to favor termites, and they tend to favor larvae of termites, which are slow moving,” says biologist Melvin Bonilla. “So they’re not super agile in terms of their hunting prowess.” Pseudos do, however, come equipped with those claws. And while they don’t have the famous stinger of actual scorpions, they use their claws to inject prey with paralyzing venom.

After several months of pupation, the harlequins emerge as adults—and the pseudos stand ready. The tiny arachnids swarm the beetles, pinching their bellies to get them to open up their wing covers, known as elytra. When the gates open, the pseudos clamber onto the beetles’ backs and hold on tight as their rides take flight.

To avoid any unscheduled skydives, the pseudos grasp at ridges on a beetle’s cuticle. Their claws also produce a silk that the pseudos will attach to the surface as a kind of safety harness (in that sense, Spider-Man firing silk from his wrists is more like a pseudoscorpion than a spider, which produces silk from its bum, but whatever).

Next comes the pseudoscorpion free love. Several males and females can end up riding one beetle, which is alright by the females, but not so great for any male that isn’t the alpha. “Usually the largest male will try to push the other males off so that he can then dominate the mating arena and use that as a way to access the females,” says Bonilla.

The male harlequin is unique among beetles in looking like it’s mad flexing in flight.

Lesser pseudos vanquished, the largest male shacks up with the females in a way that can only be described as unorthodox. Right there on the beetle’s back he’ll deposit a sort of stalk, topped with a ball of fluid that holds the spermatophore—the package of sperm. All of it looks a bit like a translucent flower, or maybe the Eye of Sauron.

Next the pseudo male grabs a female by the claw—not aggressively, mind you, just suggestively—to pull her over. If she’s into it, she’ll position herself over the flower and do a dip. “What’ll happen then is that ball of fluid will push against the spermatophore and into her sexual aperture,” Bonilla says. “And that ball of fluid will help the spermatophore stay there while the sperm is being transferred.” The male will do the same with as many other females as he can manage.

Eventually the harlequin beetle reaches its destination: another dead ficus tree. When it lands, the female pseudos disembark and develop their eggs in an external brood sac on their bellies, while the male typically stays on the beetle. The pseudos waiting in the tree climb aboard, males and females alike. Our triumphant male fights off any new males, as he did before, ideally winning the right to mate with the arriving female passengers.

Male harlequins also have to battle for females, just in a rather more dramatic way. They have those super-elongated front legs compared to the females’—limbs the males use to punt their rivals, “kind of like a hook and catapult type of device, where they try to hook the other male and catapult him away,” says Bonilla. “And usually if they do it well enough and catapult the male far enough, then that ends the battle.”

Read more at Wired Science