Flood spore

"One single Flood spore can destroy a species."

- Rtas Vadum

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 through lysogenic replication, or the host will be killed and subsquently broken down 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 and Cortana.
 * The Special Operations Elite Kusovai was horribly infected when he inhaled too many Flood spores. Given his appearance after infection, he seemed to be mutating much slower than when a victim is traditionally infected by an infection form, perhaps to say that the re-writing of a victim's genetic code for use as a combat form and later biomass is much slower when infection is due to prolonged inhalation and exposure to 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 a spore cloud. Marines that stay in spore clouds for too long will be infected 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.