The Sally Lightfoot Crab (Grapsus Grapsus) is also known as the ‘Red Rock Crab’. The Sally Lightfoot Crab is one of the most common crabs along the western coast of South America. It can also be seen along the entire coast of Central America and Mexico and nearby islands.
The Sally Lightfoot Crab is one of the many charismatic species that inhabits the Galápagos Islands and is often seen in photos of the archipelago, sometimes sharing the seaside rocks with the marine iguanas.
The Sally Lightfoot Crab is a typically shaped crab, with five pairs of legs, the front two bearing small, blocky, symmetrical chelae (chelae are also called pincers). The other legs are broad and flat, with only the tips touching the substrate.
The crabs round, flat carapace is just over 8 – 12 centimetres (3 – 5 inches) in length. They are rather flat and low to the ground and have been called ‘spider-like’ or quadratic in shape.
Young Sally Lightfoot Crabs are black or dark brown in colour and camouflage well on the black lava coasts of the Galapagos volcanic islands. Adults are quite variable in colour. Some are reddish-brown, some mottled or spotted brown, pink or yellow.
The ones seen on photographs of tropical island fauna are often bright orange or red with stripes or spots and sporting red claws and pink or blue eyes.
The Sally Lightfoot Crab lives amongst the rocks at the often turbulent, windy shore, just above the limit of the seaspray. It feeds on algae, sometimes sampling plant matter and dead animals. It is a quick moving and agile crab and hard to catch, but not considered very edible by humans. It is used as bait by fishermen.
Sally Lightfoot Crabs were sighted by Charles Darwin during his voyages on HMS Beagle.
Sally Lightfoot Crabs are usually very energetic and can be entertaining to watch.
Another crab called ‘Sally Lightfoot Crab’ is the close relative of the Nimble Spray Crab, the Flat Rock Crab, Percnon plasissimum, which only reaches a size of one inch in diameter.