Nano-gridlock and the presence of larger lifeforms (humans) seem to trigger the next stage of alien growth: the Hive. There does not seem to be any malice involved – the bacteria just reacts naturally and aggressively to any competition. The hive contains all the information and abilities necessary to set off a cascade of events that rapidly leads to full scale conflict.
Hives are large organic structures, that affix to the walls and ceiling in locations selected by the bacterium potential hive locations are usually marked by mats of visible bacteria, sometimes completely covering every surface and even stretching out across nearby rooms and corridors). Once the first is active, the Kharaa can grow new hives. After observing images brought back from the field, TSA scientists speculate that hives are actually creatures that have been evolved into this form over an incredibly long time, to serve the bacteria's ends.
Though not actually "hives" in the technical sense of the word, they do serve vital roles to the creatures they spawn, and these creatures cannot exist without them. Hives serve four crucial functions:
- spawning the five species of Kharaa (and reinforcing after death)
- advancing the abilities of Kharaa
- healing (feeding) Kharaa
- linking Kharaa into the hivesight