The Coconut Crab (Birgus latro)
The Coconut crab is the largest terrestrial (land) crab in the world! They can weigh up to 9lbs and can get over 3 ft long. They live on a number of Pacific Islands and are commonly seen knocking coconuts down from trees to crack them open; which appears to be a sign of intelligence.
They specialize in eating fruits, and nuts but they have been observed catching and eating rats and baby turtles. Unconfirmed reports have claimed that they have killed kittens and puppies!
Coconuts crabs are so well adapted biologically to life on land that they will drown if thrown in the ocean. That said, they must keep their special breathing organs (their ‘lungs’) a little moist in order to breathe properly. If they dry up, the crab will suffocate and die. As baby crabs, they have gills and can breath underwater, they lose this ability as they grow older and move into land.
They are apparently quite fast on land as well: