Insects, spiders, pseudoscorpions, and arthropods in homes.

The Pseudoscorpions, Firebrats, and Pirate Bugs That Live … in Your Home

The Pseudoscorpions, Firebrats, and Pirate Bugs That Live … in Your Home

Wild Things
Slate’s animal blog.
Jan. 26 2016 10:15 AM

The Most Disconcerting Animal That Lives In Your Home

A pseudoscorpion from Madagascar that is closely related to the house pseudoscorpion.
A pseudoscorpion from Madagascar that is closely related to the house pseudoscorpion.

Courtesy of Julia Cosgrove

According to a study published last week, your house could be home to more than 500 different kinds of insects, spiders, and other arthropods. That means jumping bristletails, firebrats, and minute pirate bugs. We’re talking about bark lice, fairyflies, and death watch beetles.

What, you’ve never heard of root maggot flies? Too bad, 10 percent of the homes sampled have them. Fungus gnats? Found in 68 percent of homes. Spitting spiders? Yeah, they’re around. And you can forget about asking them to chip in for rent.


But of all the creepy crawlies possibly crashing at your home as we speak, perhaps none is more disconcerting than the downright dastardly-looking pseudoscorpion.

Like mites, spiders, and true scorpions, the pseudoscorpions are arachnids. They have eight legs, two claws, and ticklike bodies. The good news is that they differ from their kissing cousins in one main respect—they lack a tail and the stinger that goes with it. The bad news is some species have venom glands in their claws.

Pseudoscorpions were found in 20 percent of homes in the new study, by the way. So if we can apply the findings to America at large, your odds of cohabitating with a pseudoscorpion are at least 1 in 5. Probably higher, though. Pseudoscorpions are sneaky, so the researchers probably missed quite a few of them.

Now, before you go reaching for the Kill It With Fire button, there are some things you should know about your new arachnid roommates. For starters, says Matt Bertone, an entomologist at North Carolina State University and lead author of the new study, pseudoscorpions, venom glands and all, are completely harmless to humans.


They’re too small to do any harm, to start with—a few millimeters to less than a centimeter long, says Bertone, who found his first pseudoscorpion hiding in a washcloth in his parents’ bathroom when he was young. (He shooed the arachnid into a peanut butter jar and named it Skippy.)

Now, things might be different if you were ever to find yourself in a Honey, I Shrunk the Kidstype situation. That’s because some pseudoscorpion species hunt in packs, taking down beetles and millipedes up to 30 times their size. Tiny legions have even been seen attacking and dismembering Cephalotes atratus, a tropical ant with few natural predators and armor like a shiny, black tank. Adult pseudoscorpions line up along the entrance to their colony, according to one study, “to form a nearly continuous battery of chelae,” or claws. Then, when an ant comes close, the pseudoscorpions lunge forward and grab its legs with their pincers, then quickly retreat—pinning the prey against the opening of the pseudoscorpion colony. Now that the ant is immobilized, nymphs emerge from the colony and start sawing at its joints. Every armor has its weakness.

And did I mention that pseudoscorpions can fly? I mean, not technically—they don’t have wings or anything. But they can use their claws like grappling hooks to attach themselves to creatures that do. Birds and insects are their primary flight vectors, which is why even if you’re in the middle of the Pacific on a deserted island, you’re probably still surrounded by pseudoscorpions.

What’s wild about pseudoscorpion hitchhiking is that it isn’t just an accident. They don’t simply climb onto a beetle and then say, Whoa, this thing’s moving! like that spider on your windshield. No, pseudoscorpions seek out aerial transport, or phoresy. Because of their size, it’s basically the only way for them to get to new habitats.


In fact, phoresy is so crucial to the life cycle of some pseudoscorpion species that courtship and mating take place on the beetle. This has been documented in the giant harlequin beetles, which have been seen carrying up to 30 pseudoscorpions at a time. (Can somebody please get video of this and set it to Ride of the Valkyries?)

You know how rams butt heads to determine who will get breeding rights to all the females? Well, pseudoscorpions do the same thing. Only it’s a royal rumble on the belly of a beetle. In midair. With the losers often tossed overboard. And the last pair of pincers earns himself an orgy.

Of course, pseudoscorpion sex isn’t all that sexy. The males deposit a packet of sperm and protein called a spermataphore, and then dance around it until a female becomes interested. Sometimes the male will even hold her hand-claw and sort of tug her over toward the spermatophore. If she acquiesces, she’ll sit on the packet and absorb some of the genetic material for the next generation.

At least, that’s the way the big, bruiser males want it to go. But like squid, orangutans, and many other species, there’s a way for smaller, weaker, “sneaker” males to pass on their genes even if they get booted from the beetle like it was Air Force One. That’s because neither pseudoscorpion males nor females are monogamous. And the females are capable of storing sperm from multiple males, so even if a pipsqueak pseudoscorpion isn’t her first, her last, or her only, his DNA could turn into more arachnids wherever the harlequin lands.


This is particularly good news for them, because there’s some evidence to suggest that pseudoscorpions can suffer from genetic incompatibility. This means that for some reason, certain sets of DNA just will never be able to make a baby pseudoscorpion. Other research has found that females actively seek out new mates and will eschew the advances of males they’ve already done the beetle dance with—perhaps as a way to ensure that they don’t get stuck with a single male with DNA they can’t do anything with. (For more on all of this, check out Olivia Judson’s excellent book, Dr. Tatiana’s Sex Advice to All Creation.)

I think sometimes we get so caught up with dumbo octopuses, honey badgers, and other exotic animals that we forget about the biodiversity in our own backyards.

And you better believe you have pseudoscorpions in your backyard. Lauren Esposito, curator of arachnology at the California Academy of Sciences, says she puts the chances of backyard pseudoscorpions—unless you live in Antarctica—at about 100 percent.

“You should go pull apart an old log or peel some bark off a tree and chances are you'll find some,” says Esposito, who was not involved in the study. “Most people have just never looked.”


Inside your home, pseudoscorpions may actually qualify as friends with benefits. That’s because the most common species, Chelifer cancroides, has earned a reputation as a voracious predator of book lice and springtails—small creatures known for gnawing through old books. According to Julia Cosgrove, a Ph.D. student at Harvard, Aristotle first recorded these little buggers crawling around on his scrolls.

But books and scrolls aren’t the only household items protected by household arachnids. Some species have been known to prey upon mites and moth larvae.

“Dust mites have been attributed to allergies, and moth larvae eat your clothes, so it's probably not a bad thing to cultivate some predatory pseudoscorpions in your home,” says Esposito.

But it could be even more than that, says Michelle Trautwein, an entomologist at the California Academy of Sciences and a co-author on the new domestic arthropods study. Because a survey like this has never been done before, we’re only just scratching the surface on the potential impacts the little critters might have on our lives.

“When we think about these unexplored ecosystems on the planet, we think about things like the rainforest or the bottom of the ocean floor,” says Trautwein, “but the truth is, our houses, to some degree, are these relatively new ecosystems, evolutionarily speaking. And they’re totally unexplored.”

For instance, just as a harlequin beetle may harbor a bevy of pseudoscorpions, those stowaways likely have stowaways of their own—be they mites or microbes. Who knows, the bacteria carried by pseuodscorpions could have some effect on the microbial biodiversity of our homes with as-of-yet unstudied impacts on human health. We simply don’t know.  

The point is, even if you’re squeamish about sharing your home with more than 500 kinds of arthropod—some of them pseudoscorpions—studies have shown that living with biodiversity is usually a good thing for human health. And besides, if a book scorpion is up on your shelf murdering all the lice you didn’t know you had, what do you care?

I’ll leave you with a final pseudoscorpion fact that will either win you over or lose you completely. All species of pseudoscorpion that we’ve studied have shown some sort of parenting. Sometimes that’s just mom attaching her sac of eggs to her abdomen and cleaning and protecting the embryos. Other times, it involves the mother pseudoscorpion spinning a silk chamber for the eggs to rest in.

And sometimes, when food is short and the nymphs are hangry, the mother pseudoscorpion will simply allow her young to devour her alive. She doesn’t even put up a fight. This is called matriphagy.

Is matriphagy evidence that pseudoscorpions are tender creatures, capable of the greatest bodily sacrifice in the care of their young? Or is it proof that these animals are stone cold minimonsters—be-clawed hell-beasts prowling about your bookshelf?

The answer, of course, is a matter of perspective.

Thanks to entomologist Everton Tizo-Pedroso for his help on this piece and for his work investigating the fabulously complex lives of these tiny book monsters.