Biomass is a term for large, static formations of organic materials that the swarm uses to assemble massive hive-like structures. Biomass accumulation is one of the first signs of hive formation, so it must be purged as soon as possible. Biomass is immune to bullets, explosives, and melee attacks; it can only be destroyed by incendiary weaponry (such as the Flamer , the Vindicator's incendiary grenade, and the Incendiary Mines) or the Mining Laser.

In the Jacob's Rest campaign, several clusters of Biomass must be destroyed in the SynTek Residential mission in order to proceed. Another cluster must be eliminated from Timor Station to allow the nuclear mining charge to be moved into position.

A pile of dead colonists near the Biomass in Timor Station suggests that the biomass is "assembled" by incorporating any organic material that can be acquired. This could mean that the colonists, as well as their pets and food are inside Biomass, dead or alive.


  • Biomass itself is largely defenseless and harmless, although coming into contact with it will deal minor damage and knock a marine back.
  • Be prepared for a wave of Swarm when destroying biomass.
  • Once the biomass is ignited, it will eventually die. Sustained incendiary damage is not necessary but will accelerate the process.
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