The legs of spiders move using a combination of the hydraulic pressure of body fluid and muscle flex.
Smaller spiders (usually those weighing under 3g) use a hydraulic catapult method to move around and catch prey, whereas larger spiders (those weighing over 3g) rely on a combination of a hydraulic catapult and muscle-based contraction.
https://asknature.org/strategy/leg-uses-hydraulics-and-muscle-flex/