The king crab, the pine processionary caterpillar, the lionfish and the fire ant. As far as biologists know, these four species are responsible for the fastest animal invasions in recent decades, making them the most successful invaders on the planet. In their native habitats, however, these creatures form part of the ecological balance. But introduced by man into new territories, they wipe out other species, monopolize food supplies, and can be fiercely territorial, ultimately posing a threat to the existing biodiversity.