Pedipalpi

Pedipalpi are the paired second appendages of chelicerate arthropods, located near the mouth and behind the front pair of feeding appendages (the chelicerae). The term pedipalpus is Latin, with pedipalpi as the classical plural; in English texts the plural pedipalps is also widely used. Pedipalpi vary in form and function across chelicerate groups, but most serve sensory, manipulative, or reproductive roles.

In spiders, pedipalps are primarily sensory and manipulative in females and immature individuals. In mature males, they become highly specialized copulatory organs, forming a bulb at the distal segment used to transfer sperm to the female. This male modification typically includes complex structures such as the embolus and tegulum, and their appearance is a common diagnostic feature in species identification. Female and juvenile spiders retain more leg-like pedipalps that aid in handling prey and sensing the environment.

In scorpions, the pedipalpi are enlarged pincers (chelae) used for grasping prey, defense, and mating rituals. The size and grip strength of the pedipalps can be a key characteristic in distinguishing species and ecological strategies.

Anatomically, a typical pedipalp comprises several segments: coxa, trochanter, femur, patella, tibia, and tarsus. The exact morphology and degree of specialization of the distal segments differ among groups, reflecting diverse ecological roles—from delicate tactile sensing to robust grasping. In addition to spiders and scorpions, other chelicerates display pedipalpal forms adapted to their feeding or environmental needs, illustrating the broad functional versatility of these appendages.