Harry Harrison 
Deathworld Three 
Deathworld Book 3

The planet was called Felicity. The name was a joke, except for those compelled to settle there. Inhabiting it were beings bred for thousands of years for a single purpose: to attack and kill.Jason knew this. But he also knew the planet on which he lived was moving towards certain disaster. And Felicity was the only spot in the universe where he and his companions could survive. He thought he had worked out the perfect plan. But what awaited him on Felicity went far beyond his wildest imagining.