The Goliath birdeater tarantula, the world's biggest spider, is pitted against its mighty arachnid cousin, the emperor scorpion, at more than five times its weight. Both are fierce predators, hunting insects as well as mice, lizards, and snakes. Both hiss to warn predators away. Both can defend themselves with fangs and claws, as well as venomous stingers. It is a fierce battle. Who will survive?