Spider, and Their Amazing Hydraulic Legs

A big, hairy Spider skitters across the floor of your room; its eight, long, rangy legs moving almost robotically. It stops. Horrified, you picture its fangs clicking together, and its many eyes jerkily twitching to and fro. Suddenly, the spider scuttles under your bed. Though you wait five minutes for it to reappear, it does not. Will you be able to sleep tonight, knowing that a monster lurks below?


Spiders give us the willies for a host of reasons. Their arced fangs, orb-like eyes, and segmented bodies all feed our trepidation, but the primary reason for our seemingly primordial arachnophobia likely stems from how they move. The way spiders motion their angular, jointed legs irks us like no other, psychologists say.

So why do spiders move in this unnatural, mechanical fashion? Well, it’s because they fundamentally move differently than we do. Arachnid locomotion actually makes use of the same force that powers a variety of mechanical instruments: hydraulics.

Hydraulics is the process whereby power is generated, controlled, and transmitted through the use of pressurized liquids. A basic way to understand it is to picture two liquid-filled cylinders, each topped with a piston and connected by a pipe. If you apply pressure to one piston by pushing it down, the force  transferred through the liquid to the other piston, and this piston rises with the liquid. Dump trucks, skid loaders, and pumps are all man-made machines that operate on hydraulics.

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