The Mirovs
Native mineral-eaters of Planet 65. They hang around the mines, feed on iron and gold, and get territorial. Pack hunters. Guardians are the only thing they flee — without one nearby they are scary, and a swarm can shut a shaft for days.
Not villains. Appetite.
Mirovs are native to Planet 65 and they eat minerals -- iron ore, gold, whatever the shafts are pulling up. They can sense a deposit from a long way off, they claim a site and defend it, and they destroy machinery while they feed. They hunt in packs and they breed quickly if nothing stops them. A swarm shuts a mine for days.
Three ranks, and you read them off the body
A Mirov is not one creature drawn at three sizes. The rank is marked, and the marks are specific.
A first rank carries a single chevron on the forearm and nothing on the head. A second adds chevrons to the crown tendrils, so the marking runs from arm to head. A third carries both and has grown a tail, which the lower two do not have at all.
Anyone working a shaft learns to read that in a second, because the rank of the one you can see tells you how much of the pack is behind it.
The only thing that works
Not weapons. Guardians. Mirovs instinctively flee Guardian presence, and that is the whole of the defence -- which is why the mines of Planet 65 and the seven tribes of the Guardian Islands are tied to each other however little either side enjoys it.