palpus

Palpus (plural palpi) is a segmented, finger-like appendage located near the mouthparts of many arthropods. The term derives from Latin palpus, meaning “feel” or “touch.”

In insects, palpi are typically attached to the labium (labial palpus) and to the maxillae (maxillary palpi). They are usually multi-segmented and bear numerous sensilla, which detect chemical and mechanical cues. The primary functions of the palpi are to help manipulate and sense food, probe crevices, and guide material toward the mouth; in some species they also participate in prey handling or mating-related behaviors. The size, segmentation, and degree of development of palpi vary widely across insect groups. For example, Lepidoptera often have relatively long, conspicuous palpi, while in many Diptera they can be short or reduced.

In crustaceans and some other arthropods, palpi may accompany mouthparts and serve similar sensory or manipulative roles. The presence and structure of palpi can be a useful taxonomic character, assisting in the differentiation of orders and families.

Overall, the palpus is a versatile mouthpart appendage that contributes to feeding and environmental sensing. It is distinct from other appendages such as antennae and, in some contexts, from pedipalps used by arachnids for different purposes. See also palpi-related terms such as labial palpus and maxillary palpus.