Spider legs twisted after death because of the hydraulic pressure in the muscles Bashny.Net

The spider uses hydraulic pressure to fluid circulation in their limbs - it allows him to move. If you ever see a dead spider, you probably noticed that his legs twisted, as if squeezed into a ball over his body. This occurs because the two legs of the six joints are hydraulic: to straighten the joints and, consequently, the legs, the spider reduces muscle specifically, and increases the pressure. When an animal dies, the feet are twisted automatically because nothing else makes them stand upright.

via factroom.ru