Gecarcinidae is a
family of true
crabs that are adapted for terrestrial existence, commonly known as
land crabs. Similar to all other crabs, land crabs possess a series of
gills. In addition, the part of the carapace covering the gills is inflated and equipped with blood vessels. These organs extract oxygen from the air, analogous to the
vertebrate lungs. Adult land crabs are
terrestrial, but visit the sea periodically, where they breed and their
larvae develop. Land crabs are tropical
omnivores which sometimes cause considerable damage to crops. Most land crabs have one of their claws larger than the other.