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. Crabs rely on a combination of these sense organs to find food and mates and flee predators. Distribution There are more than 50 families of crabs and 1000s of species wordwide. Most are marine, occuring in all oceans from the edge of the sea down to the greatest depths of the ocean.