Chemosensitive hairs in spiders

Abstract
Spiders possess curved, blunt‐tipped hairs on all legs and palps, which differ in many details from the straight, sharp‐pointed, tactile hairs: (1) the blunt tip is open to the outside, which can be demonstrated by high resolution microscopy and by the penetration of dyes; (2) the hair shaft has a double lumen which consists of a circular (tube) and a crescent shaped lumen; (3) this hair is innervated by two to three bipolar neurons whose dendrites enter the small tube, where they arborize into 16–20 branches. Multiple innervation and an open tip give strong evidence for a chemoreceptive function. Concluding from their position and distribution on the distal leg parts, a contact chemoreception is tentatively proposed. This interpretation is supported by the close structural analogy to the known contact chemoreceptors in insects. Observation of behavior indicates the importance of a contact chemoreceptor on spider legs. Other possible chemoreceptors in spiders which have been described previously by other authors are discussed.