The large front appendages used by spiders and scorpions for sensing or grasping are pedipalps.
Pedipalps are the second pair of forward appendages in chelicerates, positioned beside the mouthparts and ahead of the walking legs. Their form differs dramatically among arachnids. In spiders, they are usually short, leg-like structures equipped with sensory receptors for detecting chemical and tactile information. In mature males, the pedipalps become specialized reproductive organs that transfer sperm to the female.
Scorpions modify their pedipalps into prominent pincers, technically called chelae. These grasp prey, help with defense, and can play roles in courtship and sensing the environment. Their pincers are not the same as the chelicerae, the smaller mouthparts near the front of the body.
This distinction causes a common mix-up: “mandibles” belong to insects and crustaceans, while “spinnerets” are silk-producing structures found in spiders. Pedipalps occur across several chelicerate groups, including scorpions, pseudoscorpions, whip spiders, and horseshoe crabs, although their shapes and jobs vary.