palpi

Palpi, or palpus (singular palpus), are paired, segmented appendages located near the mouth in many arthropods. They are primarily sensory and manipulative structures, bearing tactile and chemosensory receptors that help animals sample substrates, assess food, and guide it toward the mouth. The specific morphology of palpi varies widely among groups.

In insects, the main palpi are the maxillary palps and the labial palps. The maxillary palps arise from the maxillae, and the labial palps from the labium; both consist of multiple segments and often bear taste sensilla. Their length and segmentation can differ markedly among orders. For example, in some Lepidoptera the palpi are conspicuously long and forward-projecting, aiding in odor detection and nectar foraging, while in other insects they may be reduced or modified for particular feeding strategies.

In arachnids, the term palpus is often used interchangeably with the pedipalp—the first pair of appendages near the mouth. Pedipalps are multifunctional and can act as sensory organs, assist in feeding and prey manipulation, and, in male spiders, house specialized structures used to transfer sperm during mating.

Development and evolution of palpi reflect their functional diversity; they are generally considered to be modified appendages derived from proximal limb segments. Their morphology—such as segment count, articulation, and distal structures—provides important characters for identifying species and understanding relationships among arthropod groups.

Palpi thus occupy a key role in feeding biology and sensory perception across many arthropods, with significant variation that informs taxonomy and phylogeny.