A strict hierarchy has been maintained, for eons, by the strength of claws against the strength of shells. The ability to kill and resist being killed are all that determines status. Winners devour losers, strengthening their shells and claws with with cannibalized minerals.
They lack whatever that certain something is that allows for true originality. All of their technology is trial-and-error derivations on the scavenged work of others. They would never have left their planet, were it not for the unfortunate crash of a survey vessel. They discovered the wreck, and applied their stubborn form of non-intelligence to it. Within the century, they were starfarers.
Emergency beacons from long lost ships draw victims towards isolated asteroids, and would-be salvagers and rescuers alike find themselves in a rapidly strengthening gravity well, until they are crushed against the surface. Then the shipbreakers will emerge, never engaging in combat, but attacking survivors indirectly, sabotaging life support, setting traps, and waiting. When there are no more survivors, they will disassemble the wreck, reset their trap, and begin to reverse engineer anything new.
Now their shells are steel and their claws are torn from military robots, but they still live by their ancient code: take the strengths of those you kill, hide from those you can't.