Why daddy longlegs are one of the most misunderstood creatures

There’s a pretty pervasive myth that goes something like this: “Daddy longlegs are the most venomous spider in the world, but their fangs are too small to pierce human skin.”

Sound familiar? Well, this little nugget of conventional “wisdom” is not just incorrect. It’s spectacularly wrong on three separate counts. 

Are daddy longlegs spiders?

Daddy longlegs are arachnids that have tiny, pill-shaped torsos and legs that go on for days. They have a pair of shoddy eyes, breathing tubes known as trachea, guts for digesting, and even secret, trap-door genitals, but really, for the most part, these animals are just an absolute mess of legs and the chunky thing those legs connect to, like bicycle spokes to a hub. 

Despite their appearance, daddy longlegs are not spiders at all. Like mites, ticks, and scorpions, daddy longlegs are spider cousins. Which is to say, daddy longlegs are arachnids that belong to the order Opiliones, not Araneae (where the spiders are classified). 

Furthermore, spiders usually have eight eyes, while daddy longlegs usually only have two, each of which is rudimentary and can only see light and dark but probably not the look on your face when you spot it on the wall of a port-a-potty and run away screaming. Likewise, if you look at the animals from above, spider bodies have two main parts—the cephalothorax and the abdomen, with a waist in the middle. Daddy longlegs bodies are usually scrunched together into one part.

“Spiders look like they’re wearing a little corset. Opiliones just let it all hang out,” quips Mercedes Burns, an evolutionary biologist and Opiliones expert at the University of Maryland at Baltimore County. 

But perhaps the easiest way to tell a longlegs from a spider? “If it’s in a web, it’s a spider, because Opiliones can’t make silk,” says Burns. 

Can a daddy longlegs bite kill you?

Getting back to the “most venomous spider on Earth” bit, well, you can stop worrying about daddy longlegs bites, because these creepy-crawlies don’t even have fangs. “Their mouthparts look like little scissors,” says Burns. “And they use them to cut off little pieces of food and put them into their mouth.” 

That bit about the potency of daddy longlegs venom? It’s utter hogwash. Because daddy longlegs don’t have venom. Not even a little bit. 

(What’s the difference between a poisonous and venomous animal?)

Add it all up, and I’m telling you that daddy longlegs are physically incapable of causing you harm. You could dive into a swimming pool filled with the things and come out without a scratch. Though, with that many wispy legs, you might have to worry about death-by-tickle. 

Daddy longlegs shed their legs to survive

Speaking of those legs—a closer look reveals that daddy longlegs patellae, or knees, sit way up high in the air, suspending their body above the ground in a way that gives them an extremely low center of gravity, says Burns. This allows the arachnids to remain stable as they bounce around on legs that are less like rigid stilts and more like bungee cords. Below the knee, each leg has something like 18 to 20 tarsal segments, all of which bend and allow the leg to grab onto everything from a tree branch to a blade of grass. “It’s almost like if your feet could wrap around things,” she says. And, you know, if you had eight of them instead of two.

“Their second pair of legs have lots of sensory structures on them. And they use them to kind of tap around as they’re walking,” says Burns. “They can walk on those legs, too, but they don’t prefer to because they use them to feel their way around, maybe even tasting and smelling the surfaces that they’re coming into contact with.” 

Sometimes, the legs end in hooks, the better to grapple with, and some species even produce a kind of glue on their appendages that they use to catch prey in wet places, such as waterfalls. “I kind of think of them like a jack-of-all-trades,” says Burns. “They’re an all-terrain arachnid.” 

Now, as anyone who has ever tried to squash a daddy longlegs knows, their legs fall off their bodies so willingly, it’s almost as if the arachnids want to be rid of them. But leg loss is a feature, not a bug. 

(Here's how animals thrive with three legs)

“We regularly find Opiliones out in the environment that have lost legs,” says Burns. “And they’re still able to locomote just as well as individuals that have all eight.” In fact, she says they can get by with as few as four legs, which means that even if they don’t have the nine lives that cats supposedly do, they at least have four. Because lost legs are do-overs. 

When a predator (or curious little kid) gets hold of a daddy longlegs, it’s likely to focus its attack on one of the arachnid’s legs. And since the poor critter doesn’t really have any weapons to defend itself with, it’s left with a choice—stay and die or cut its losses and run. This is why Opiliones legs are so incredibly easy to detach. They’re basically designed to snap off and do so cleanly, lest the arachnid bleed out in the process. Once plucked, the leg also jumps around as the nerves continue to fire—a potential leave-behind distraction that occupies the predator while the now- slightly-less-leggy one makes its escape. Scientists call this leg-jettisoning ability autotomy. 

Again, all of this seems wildly counterproductive to survival, but it’s worked for the Opiliones for hundreds of millions of years. In fact, while we tend to point to animals like cheetahs, falcons, and blue whales when discussing the pinnacles of evolution, there’s a hell of a case to be made that the supremely strange arrangement put forth by these arachnids may just be one of the most successful body forms on Earth. 

(Why these gigantic spiders love to be near traffic)

“These things have existed for a really long time,” says Burns. In fact, the first Opiliones fossils hail from 405 million years ago, which makes the order one of the oldest terrestrial animal groups. “But their bodies are more or less unchanged since then,” says Burns. “I don’t ever want to call something a ‘living fossil,’ because if it’s alive today, it’s still evolving. But it’s an indication to us that their body is pretty robust to evolutionary and environmental change.” 

In other words, evolution looked at the daddy longlegs and said, “If it ain’t broke, don’t fix it.”