Abstract: Mechanoreceptors play a vital role for animals to sense and monitor environmental parameters, like flow speed, tactile resistance, and pressure. The hairy-structured trichoid sensillum, a common type of mechanoreceptor in insects, is generally non-motile, embedded in a socket connected with cuticular substrate. However, we discover that the trichoid sensilla on the tongue of western bees (Apis mellifera L.) is rotatable and can be actively maneuvered by bees. The trichoid sensilla together with the socket base are mounted on the origami-like sheath of the tongue, and can rotate outwards along with the deformation of the tongue sheath. We illustrate that the rotation of the tongue sensilla hairs can locally generate shear force in the liquid to sense the viscosity, which may facilitate bees to adjust their feeding strategies. The viscosity sensitivity of the rotatable trichoid sensilla based on the origami-like mechanism, according to our mechanical model, is 13 times greater than that of the fixed sensilla. In addition, our finite element analysis shows that strain would concentrate on the trichoid sensilla base when rotating in the liquid, which may structurally enhance its perception sensitivity. This study reports a new mechanism of active mechanoreceptors and may have implications for origami mechanisms with correlative functional components, especially for micro-robotic systems used in underwater viscosity sensing.

Key words: Honey bee , · Mechanoreceptor , · Active sense , · Liquid viscosity , · Origami