Flood
From Halopedia, the Halo wiki
Summary
The Flood are a group of parasitic life forms that work to consume everything with sufficient biomass in the galaxy. In natural form, The Flood are reletively harmless. However, after attaching themselves to a host body, they decay and mutate the body to be a soldier or to perpetuate the Flood species by incubating Flood eggs until they've fully developed.
Next to nothing is known about their origin. Some have suggested that the Flood were a weapon of mass destruction that grew beyond their masters ability to control. Others think that they are some kind of primitive life form accidentally discovered by an ancient race. However, their destructive ability is not to be doubted.
The Flood were kept by The Forerunners for scientific study on the Halos.
Flood Forms
Also:
- Flood Juggernaut - Removed from Halo 2.