The colony is a deploying immobile unit capable of deploying more drones than a snail. It has no function on its own, and can be destroyed very quickly.
Colonies are dangerous and frustrating units. It has very low health and defenses, the player cannot see what enemies are inside, are very common and deploy a full half as many units as enemy snails (9, 6), takes its own turn despite the fact that it can't act in any way, and can easily be defeated before enemies are deployed. Destroying a colony before enemies are deployed heavily downgrades rewards, especially cards, to the point that if one enemy is not deployed, it could take away 3-4 cards. Colonies often deploy soldier units, but can deploy any drone, even and especially higher drones like butterflies, rhino beetles, and dragonflies.