Though it’s only 2.8-4.3 inches wide, the terrestrial crab Johngarthia lagostoma is the largest native land animal on Ascension Island, one of four islands in the South Atlantic where it’s found. Since these crustaceans cannot swim, the method by which they arrived on an isolated island like Ascension remains unknown–though some speculate that smaller islands, now underwater, could have helped these crabs arrive at their current homes. Species introduced by Europeans in the 19th century, include mice, rats, and rabbits, now compete with these endemic land crabs.
On Ascension–a volcanic island–most of the crabs are yellow-orange, but some are dark purple, which may help them hide from predators. Their larvae are marine, and adults migrate to the water in the rainy season to release their offspring, with mating taking place along the way. During this time, as the crabs travel from their range in the mountains to the sea, they can cover roughly 1,480 ft per day.