The eyes are on stalks which can be lowered for protection into sockets on the carapace. Crabs appear to see very well with some species detecting movement 20 or 30 metres away. Crabs can also hear and produce a variety of sounds. In courtship some species attract the females attention by banging their cheliped on the ground or vibrating their walking legs. Each species has its own unique sound that can attract a female or intimidate a competing male.
Crabs have bristles and hairs which act as touch receptors .
The bristles occur all over the body but are most frequently found in clumps on the walking legs. These bristles signal contact with a hard surface simply by bending, whilst other shorter hairs are sensitive to water currents. Crabs can find food using chemical stimuli . When similar detectors on the legs contact food the cheliped quickly grasps the object and passes it into the mouth. Crab mouthparts have further receptors which are sensitive to particular chemicals.