Nerdfighteria Wiki - Why Do Spiders Curl Up When They Die? (2024)

[♪ INTRO].

Ever gone to sweep up your floor and noticed a little dead spider mixed in with the dust bunnies? If you paused for a closer look, maybe you noticed that its tiny legs were curled up tight against its body.

This spidery leg-curl of death happens because spiders don’t use muscles to extend their legs. They harness the power of fluids instead! Spider legs are basically a series of little tubes.

The joint where these tubes connect to the body, what you could think of as the “hip”, works much how you’d expect. It’s equipped with both extensor muscles to extend the legs and flexor muscles to curl them in. So, paired muscles that work against one another.

Like how your biceps and triceps allow you to both flex and extend your forearm. But the other joints in spiders’ legs only have flexor muscles. To straighten out those joints, spiders pressurize them by pumping them full of hemolymph, the spider equivalent of blood.

Some scientists think the evolutionary reason for relying on hydraulics is that getting rid of extensor muscles leaves room for bigger, more powerful flexor muscles. And that curling-in motion of flexors is what spiders use to grip their prey and climb your basem*nt walls. So, not having to bother with extensors lets them really maximize their flexing abilities.

Spiders can even use their unique leg anatomy to power mighty leaps. First, they pressurize their leg joints while contracting those flexor muscles. Then they suddenly release them, and the near-instant extension launches them into the air.

But when a spider dies, its body experiences all the usual side effects of death, including rigor mortis. That’s when a corpse becomes stiff because its muscles contract. And it happens because a dead body stops producing adenosine triphosphate or ATP, the energy source that powers our muscles.

ATP interacts with calcium ions and some specific proteins to control the action of muscles. There’s a lot going on at the molecular level here, but the key thing to know is that you need ATP for the muscle to relax. Since a dead body stops producing ATP, the muscles soon run out of the stuff, so they get stuck in clench mode until they decompose enough that rigor mortis ends.

And, for a spider, being dead also means no more pressurized hemolymph. So there’s nothing to combat the flex of those legs, which is why they end up permanently curled. Now, if the thought of spiders stuck in the tell-tale death pose makes you a little sad, maybe this will cheer you up:.

Spiders’ hydraulic legs are so cool that some scientists are taking inspiration from them to design robots with joints that are powerful but lightweight and flexible. So the next time you spot a curled-up spider, just imagine that its legacy is an awesome giant spiderbot! Thanks for watching this episode of SciShow!

And specifically, thanks to our patrons on Patreon. Without their support, we wouldn’t be able to do what we do here, from covering the science news you need to know to answering quick questions like this. So, thanks patrons!

And if you’re not a patron but would like to learn more about joining our community of science lovers, you can head to Patreon.com/SciShow. [♪ OUTRO].