How do spiders regenerate a lost leg?

Spiders, like many other arthropods, possess the ability to regenerate lost limbs. This process is closely linked to molting, the periodic shedding of the exoskeleton that allows the animal to grow.12

When a spider loses a leg—sometimes through autotomy, a defensive behavior where the animal intentionally detaches an appendage to escape a predator—the regeneration process begins. A new, albeit initially smaller, limb develops beneath the old exoskeleton during the premolt period. This new leg remains confined until the spider undergoes its next molt, at which point the old skeleton is shed and the regenerated limb emerges.3421

It is important to note that because most spiders cease molting once they reach sexual maturity, they generally lose the ability to regenerate lost appendages as adults. Consequently, successful regeneration is typically limited to the immature stages of the spider's life cycle.21