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Biomass is biological matter that can be used by the zerg in order to evolve the Swarm.

Game Effect[]

Left 2 Die[]

In the official arcade map Left 2 Die, biomass is used as a resource, and is obtained by killing special zerg units and destroying infested buildings. A science facility can be used to spend biomass in new units, structures and upgrades.[1]

Heart of the Swarm[]

In the Heart of the Swarm campaign, biomass is used both for primary mission objectives and as optional objectives to gain levels for Kerrigan, effectively replacing mutagen from earlier in development.[2]

Co-op Missions[]

Biomass ready to be collected

In Co-op Missions, Abathur gains biomass from destroyed enemy units. This allows the creation of upper tier units such as the brutalisk and leviathan. Abathur's combat units (excluding overseer) gain increased 3% life, 1% attack speed, and 1% Biotic Leech effect (restore life per percentage of damage) per stack of biomass. Except other combat units, swarm hosts gain only increased life per stack of biomass, but it's spawned locusts gain increased life, attack speed, and Biotic Leech effect per stack. Some units get additional effects per stack of biomass, namely: roaches gain increased 0.05 armor per stack, swarm queens and vipers gain increased 5% energy regeneration per stack, ravagers gain 0.5% Corrosive Bile cooldown reduction per stack, and swarm hosts gain 0.5% Spawn Locust cooldown reduction per stack. The drop rate of biomass depends on the mission difficulty, on casual and normal, it will drop 5 biomass per supply, on hard it will be 4, and on brutal it will be 2.5. Biomass in a range of 4 of each other will merge into one pickup. Neutral Critters also generate biomass (however, killing a critter by "critter nuke" won't generate one).

Units given to Abathur by mutators (confirmed for the Archangel at least) can also accumulate biomass and get buffs.[3]


On an island on the east side of the map "Old Soldiers", there is an outhouse labeled "Terran Biomass."


  1. Blizzard Entertainment. StarCraft II. (Activision Blizzard) Map: Left 2 Die (in English). 2011.
  2. Blizzard Entertainment. StarCraft II: Heart of the Swarm. (Activision Blizzard). PC. Mission: Heart of the Swarm, Enemy Within (in English). 2013-03-12.
  3. Co-Op Mutation #267: Violent Night. StarCraft 2 US Co-op Forums. Accessed on 2021-06-06.