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Why Do Spider Legs Curl Up When They Die?

As an associate certified entomologist and a rock climber, I get plenty of climbers envy when I study insects and arachnids. They have different body structures that make the feet of scaling a vertical or overhanging wall much easier. During a climb, I heard a loud pop and learned about pulleys in humans. This painful process highlighted a key difference between humans and spiders. It lies in the answer to the question: Why do spider legs curl up when they die?


Pulleys are a key part of the human musculoskeletal structure that allows our digits to curl and bend as we wish. They act and are structured similarly to the rings on a fishing pole that guide the line (in our case tendons) along. As tension is created, it pulls on the pulleys and bends the pole (or finger bones) according to the force.

Interestingly enough, spiders do not have pulleys despite their ability to bend and curl their legs.


There is a different locomotive process at work in spiders that is much more related to machines. Many machines work on the principles of hydraulics. Changes in liquid reservoirs create the force necessary to move tons of material via machines. Spiders work on a similar principle.

Spider legs work on the principle of hydraulics. As spiders increase the pressure in their bodies, they cause their legs to straighten

What About Jumping?

Thinking about hydraulics moving spider legs is interesting to imagine. It is impressive that they evolved into such a smooth moving creature. They are also incredibly fast for this type of locomotion. One step further is thinking about jumping and how that functions.

Jumping spiders are known for their quick movement that consists of leaps and bounds rather than methodical steps. They achieve this by increasing the blood pressure in their body suddenly to increase the hydraulic pressure especially to their hind legs. The quick and sudden increases in pressure provide the force necessary to shoot forward.

So Why Do the Legs Curl Op When They Die?

When the spider dies, the hydraulic system shuts down and the legs curl up into their decompressed state. It is as simple as that.

Controlling Spiders

If you are like most people, you couldn’t care less about any spider bodies or why they work like they do. Most people I know would rather that spider bodies just fail to work completely. Important components of spider control include:

  • Controlling their food sources
  • Reducing moisture
  • Managing light
  • Removing webs
  • Proper identification
  • Monitoring
  • Controlling the spiders directly with dusts, sprays, granules, etc.
  • Exclusion

If you need help with any part of the spider control process or want to turn the entire process over, the experts at Rove Pest Control are available to help.