Infestation pustules are masses of zerg biomass that would often block entrances of infested structures. They were largely composed of creep. Several are located in Tarsonis City on Tarsonis, blocking the entrance to skyscrapers. During the feral zerg occupation of Antiga Prime, a similar growth was used to block some of the exits of the New Andasar Subway.
Infestation pustules serve as blockage for objectives on the maps "Enemy Intelligence" and "Flashpoint." In "Enemy Intelligence," they block the points on the first section of the map where units must garrisoned. Once destroyed a beacon will appear in its place.
In "Flashpoint," these pustules serve as blockage for the subway that runs across the map. Destroying them allows the quick deployment of forces across the map.