The coconut crab, Birgus latro, is a species of terrestrial hermit
crab, also known as the robber crab or palm thief. It is the largest
land-living arthropod in the world, and is probably at the upper size
limit of terrestrial animals with exoskeletons in today's atmosphere
at a weight of up to 4.1 kg (9.0 lb). It is found on islands across
the Indian Ocean and parts of the Pacific Ocean as far east as the
Gambier Islands, mirroring the distribution of the coconut palm; it
has been extirpated from most areas with a significant human
population, including mainland Australia and Madagascar.
The coconut crab is the only species of the genus Birgus, and is related to the terrestrial hermit crabs of the genus Coenobita. It shows a number of adaptations to life on land. Like hermit crabs, juvenile coconut crabs use empty gastropod shells for protection, but the adults develop a tough exoskeleton on their abdomen and stop carrying a shell. Coconut crabs have evolved organs known as "branchiostegal lungs", which are used instead of the vestigial gills for breathing. They cannot swim, and will drown if immersed in water for long. They have developed an acute sense of smell, which has evolved convergently with that of insects, and which they use to find potential food sources. Mating occurs on dry land, but the females migrate to the sea to release their fertilised eggs as they hatch. The larvae are planktonic for 3–4 weeks, before settling to the sea floor and entering a gastropod shell. Sexual maturity is reached after about 5 years, and the total lifespan may be over 60 years.
Adult coconut crabs feed on fruits, nuts, seeds, and the pith of fallen trees, but will eat carrion and other organic matter opportunistically. The species is popularly associated with the coconut, and has been widely reported to climb trees to pick coconuts, which it then opens to eat the flesh. While coconut crabs can climb trees, and can eventually open a coconut collectively, coconuts are not a significant part of their diet. Coconut crabs are hunted wherever they come into contact with humans, and are subject to legal protection in some areas.
To add onto that, I freakin love these things. Damned crab-tanks! TANKS! If you walk around at night you don't even have to look for them because you WILL hear them! *CLANK CLANK CLANK* They kind-of sound like when you toss a brick or a lava rock at the ground. That *clunk-crack* sound? That's them.
They call 'em Robber Crabs because they will STEAL anything they can get away with. If you leave a door open or even a window that's close to a trash can or whatever, they'll come in and try to get stuff.
If confronted they'll spin and retreat, back first with claws at the ready. They don't want to fight. They will run away if you let them so if you ever see one just turn to it and take a step. They run like crazy.