Spawners are pure forms that gestate new infection forms in their diseased brood sacs, releasing swarms of new parasites. Spawners are an example of Flood adaptation, a war-form created specifically to counter the defensive measures of the Ark and Banished.
Highly mobile and capable of independent action, these creatures venture out from High Charity to spread the Flood deep into nearby refugia. Most pockets of Flood infestation Spawners establish will be detected and quickly destroyed, but time and probability is on the parasite's side.
The Spawner lurks at the rear of Flood assaults, spawning waves of infection forms. Spawners must be quickly dealt with, or they will continue to create Flood attack forces just outside the range of base defenses.