Why Do Spider Legs Curl Up When They Die?

You’ve likely encountered a few dead spiders in your living space throughout your lifetime. No matter the species, one thing is common: the lifeless creepy-crawlies usually have their legs curled up. Curious minds may wonder why, and the answer has to do with the arachnid’s circulatory system.

1. What Makes Spider Legs Curl Up When They Meet Their End?
2. Is a Spider With Curled-Up Legs Always Dead?

What Makes Spider Legs Curl Up When They Meet Their End?

According to Sciencing, a spider’s body is similar to a hydraulic system, or a machine that uses pressurized liquid to power something. In the case of spiders and many other invertebrates, the liquid in question is called hemolymph, which is the equivalent of blood found in vertebrates. 

Because an arachnid doesn’t have muscles for leg extension, the creature must rely on a hydraulic chamber to pump hemolymph through its limbs so it can stretch them out. Spiders can control the flow of the fluid so they can curl their legs when they want. For example, they may rapidly increase and then decrease their hydraulic system when reaching for their prey and gripping them tightly.  

But, of course, spiders lose control of their bodies when they’re dying or are already dead. The lack of hemolymph pressure causes their legs to curl inward permanently. 

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Is a Spider With Curled-Up Legs Always Dead?

Curled legs are the most obvious sign that a spider is dead. However, spiders are also clever tricksters. Per the No Bugs pest control experts, some species—such as the male nursery web spider—will play dead to attract female companions; others might fake death to counterattack or escape an enemy. It’s also possible that a spider can be dehydrated or stressed when they pretend to be dead. 

You might be tempted to kill any spiders you spot in your home, but scientists say you shouldn’t. The eight-legged creatures will help catch other unwanted bugs.