|Land crabs are "true crabs" that have adapted to a terrestrial lifestyle. The undersides of their gill plates have a network of blood vessels that extract oxygen from the air. They still have the traditional gills of crabs and have to return to the seas for breeding and normal larval development. Their breeding is highly synchronized with the lunar and seasonal cycles, and mass movements of crabs have been observed. They are mid to large size crabs and many have deep brilliant colors. On land, they have been known to eat and destroy crops.