Flood spore

"One single Flood spore can destroy a species."

- Rtas Vadum

Flood Spores or Virus Forms, are the stage in a Flood Infection Form's life, when it is airborne. Once a Flood Infection Form, the first stage in the lifecycle, has consumed enough biomass or infected enough hosts of sufficient biomass, it will become airborne and now, every host it comes into contact with, will multiply into millions of spores and become pure Flood Biomass, or a Pure Form, a hardier breed of Flood. One can assume that the central intelligence core of each Gravemind is a super-massive cluster of Flood Spores powering it and it's biomass, leaving us to ponder, "is it the Gravemind controlling the Flood, or are Flood Spores themselves the embodiment of pure Flood?" Flood cannot exist for very long outside of Spore Clouds.

Flood Spores are the most basic of Flood forms that are crucial in the formation of Flood hives. Spores are also used as methods of suffocating future hosts and clearing the area of uninfected hostiles. It is not known if spores take a specific form or if they are just any type of floating Flood biomass. Spores linger through the air clogging air filtration systems and making it easier to infect hosts. If a spore lands in an area that can support it, it will form Flood Growth Pods. If the area does not have enough biomass to support a Flood Growth Pod, the spore will spread over floors and walls until it covers as much as it can. It is possible that if a non-infected host inhales or becomes covered with these spores, then the host may be infected or the body will be dissolved into the necessary nutrients demanded for the Flood to create the various forms needed at the time.

Trivia

 * You can see Flood spores in Halo 2 and Halo 3 on levels where there is massive Flood infection, such as Quarantine Zone (Level) and Floodgate (Level).
 * The Special Operations Elite Kusovai was horribly infected when he inhaled too many Flood spores.
 * In Halo Wars they are referred to as "spore clouds", and they only appear after a Flood Growth Pod has been destroyed, or a Flood Launcher fires flood biomass at your units and when it strikes the ground it will sometimes release spore cloud. Marines that stay in spore clouds for too long will die and become Human Combat Forms.
 * It is of note that when SPARTAN-117 and the Arbiter were held captive by the Gravemind, the Arbiter would have most likely inhaled many spores, due to the fact that the Gravemind was exhaling them. SPARTAN-117's helmet would have filtered them out of any air that his armor took in. It is possible, but very unlikely, that the Arbiter's Armor or shields protected him. The Gravemind may have also made sure not to infect the Arbiter, since he needed him for the Index.