Courtesy of Ed Nieuwenhuys.
Spiders have a peculiar system by which they move their legs.
Spiders, on the other hand, use the same technique as in robots or car brakes - hydraulic pressure. It has been known for long that spiders cannot extend their legs with the aid of muscles. But the method by which they actually extend them was still to be revealed. However, it was revealed that no leg extension by elastic forces occurred. Then it had to be hydraulic pressure.