Flood

The Flood Inferi redivivus


Sapience level	Varying sapience
Average height	Varies by form
Diet	Carnivore
Population status	Endangered
Danger rating	Lethal
Subspecies	Forms — see below ↓
More Halo species

The Flood, or "The Parasite" as they are known to the Covenant, are a species of highly virulent parasitic organisms that reproduce and grow by consuming sentient life forms of sufficient biomass and cognitive capability.

The Flood are an extremely adaptable, dangerous, and expendable parasitic life form. It is the most variable species of the galaxy, as it can infect and mutate both Humans and Covenant species (such as Elites and Brutes) into Combat Forms. The Flood is thus widely considered to be the greatest threat to the existence of life, or rather, more accurately, biodiversity, in the Milky Way Galaxy.

Anatomy and appearance[]

The Flood, a virulent species of parasites, is an anomaly in all known biology, and an anomaly to regular life. This may be explained by its nature as an extragalactic species, originating from a different galaxy. It is extremely adaptive, and mutates hosts through different stages of accelerated "evolution", where the body of biomatter accelerates its own evolution to the point of a massive biological breakdown, where by the infection can first take place. The species can reproduce without host bodies, though this is described as a last ditch effort, and only performed by pure Flood forms.

The only known pathway for Flood reproduction and survival is by the infestation and assimilation of other species. They do this through a form of cellular reproduction known as lysogenic replication where the viral cells infect host cells with their own genetic code which mutates the host cells into viral forms. Capable of surviving extreme environments ranging from -75 to +53 degrees Celsius and even underwater (in early stages of life), the Flood can withstand harsh environments of all known colonized planets.

It would seem that the Flood can infest any living organism, but that they prefer hosts with a large brain capacity to accelerate the formation and expansion of the Gravemind hive intelligence and the Flood intelligence as a whole. They are only as intelligent as the beings they infect; the more cunning the enemy, the more dangerous the Flood will be.

As the Flood spread and replicate, they will alter the environment to better suit their needs. This takes the form of biomass growing on any available surface, and the air being filled with spores. This appears to be part of the Flood life cycle and is done automatically, and leads to the development of a Gravemind and a Flood Hive.The Flood seem to thrive in moist and humid areas, which lends itself to the fact the the Quarantine Zone is bereft of organic life, and is cold and perpetually snowy, to hinder the development of the Flood.

Behavior and intelligence[]

Infection forms selectively target other species that possess sentient intelligence and are of sufficient biomass, and can infest living or lightly wounded dead bodies. Infection forms have long tendrils that pierce the skin of the host and find their way to the spinal cord. From here they synchronize with the host, matching frequencies with the host's nervous system and killing them almost instantly.

From there, they take control of the host body, replacing whatever mind originally resided there with the ravenous and voracious psyche of the Flood, although certain higher-level cognitive abilities, such as combat techniques and technical knowledge which may be useful are retained, scanned from the victim's brain after death. Despite this lingering of certain memories, no trace of the original mind's personality remains; only a simplistic and primal urge to assimilate or destroy other species drives the organism after infection.

In isolated cases, such as when the Flood seek very specific information from an individual's mind, they utilize an alternate, undescribed method of infestation that does not kill the host immediately; this allows the Flood to "burrow" into the host's mind, eventually giving them access to the entire scope of the host's memories.

If a greater Flood intelligence, such as a Gravemind, is activated, then it is capable of overriding the primitive instincts of all other Flood forms, taking direct control of each and every Flood organism and making them much more dangerous as a result of being guided by a sentient mind. It is unknown what would have happened to a still-living host such as Private Jenkins when a Gravemind attempted to influence control over it, as no living hosts were ever encountered after the activation of a Gravemind. In addition to controlling the physical movements of the host body, the Gravemind can utilize the vocal cords of combat forms made from former Jiralhanae, Humans, and Sangheili to communicate.

A Gravemind starts out as a Proto-Gravemind -- a Flood form created by merging the bodies and biomass of numerous sentient life forms; some Flood forms may also be repurposed and merged into the Proto-Gravemind. After a Proto-Gravemind has been created, nearby Combat Forms will continue to supply it with fresh bodies, allowing it to accumulate mass, increase in size, and gain more memories and intelligence from consumed hosts. Eventually, the Proto-Gravemind reaches a certain critical mass and becomes self-aware—a Gravemind. This critical mass tends to be made up of thousands of bodies if using human-sized bodies as a measuring unit.

The Gravemind, and its subordinate Flood infection, will then continue to accumulate. Eventually, when the Flood infection has become too large for even the Gravemind to control—or when no life remains in the galaxy—the Flood infection will reach the Intergalactic Stage, and Flood will leave the galaxy with the intent to create a new Gravemind elsewhere.

Flood forms[]

The most basic form of Flood evolution is the infection form, unique in its distinctive spherical shape. The infection form is used to infect organisms of other species, physically adhering to their surfaces and inserting tentacles, forcibly "hacking" into its host's nervous system, completely changing its psychology to that of the Flood's, and eventually physiologically mutating it into one of the various parasitic Flood forms of whatever the victim may be.

Infection[]

The Flood Infection Form might appear at first glance to be little more than a harmless and repulsive creature, but once it gains physical contact with a biological host, it becomes an instantly deadly foe. Small tentacles underneath its body penetrate the skin, tap into the victim's spinal cord, and unleash an attack on the host's nervous system via direct contact with the spine, killing the host almost instantly, but in rare cases the victim is still conscious.

Once this is accomplished, it rewrites the neural pathways of the victim's brain with its tendrils, forcing a resonant frequency match between its neural signals and the host's. Then it releases the Flood Super Cell which overwrites the host DNA and causes rapid mutation. After this is accomplished, it starts to physically move the body, liquefying the organs to create the tentacles on the left hand from the calcium obtained and finally nest itself within the chest cavity of its host. All this can happen within a matter of seconds.

If infection of a specific creature is not possible, that being will be totally ignored by the Infection form, leaving other Flood forms the task of killing it, although it is likely that the Flood will use the incompatible body for later sustenance. An Infection Form may also abandon its host if the corpse has been heavily damaged, and look for a new one. Several Infection Forms, sometimes ranging from 5 to 15 Infection Forms at once, can attack certain victims. Infection forms appear at first glance, to be quite small, but if you compare them with the average Human, you can see that they are actually quite large; roughly the size of a man's torso.

Carrier[]

Carrier forms are formed from older Combat Forms or from bodies that are unsuitable for combat. Combat Forms can be converted when they reach the end of their life span, or become too damaged to fight. Carrier Forms perpetuate the Flood species by acting as incubators for newly created Infection Forms and keeping them safe until they're fully developed. Eventually, when a Combat Form has lived long enough, it will also evolve into a carrier, regardless of its status.

Once the Infection Forms are ready, the carrier simply explodes spontaneously, sending the new Infection Forms flying into the air. As soon as the Infection Forms are released, they begin searching for new hosts. It should be noted that Carrier Forms won't wait until full maturation has occurred. If potential enemy hosts are nearby, it will simply get close to them and explode, sending the Infection Forms flying at the unsuspecting and often injuring or killing enemies. The explosion of a Carrier Form is similar to the explosion of a grenade, and deals damage to anything nearby.

Combat[]

A Combat Form is not a natural organism, but rather a mutated host infected by parasitic Flood Super Cells implanted by an Infection Form. Successful creation of a Combat Form requires a host with sufficient biomass and calcium store, and an infection form to infect the host. After mutation begins, the infection form attaches with one of its tentacles, which it uses to establish a neural connection that allows it to command the host's nervous system, thus rendering command of the legs and arms useless. During the infection process, the host's internal organs are liquefied and the nutrients from them are used to develop the tentacles and other appendages.

Once fully transformed, the Infection Form has total control over the host's body and changes the physical appearance of the host to better suit its own needs (although an infected host will be roughly the same size as it was before). Combat Forms retain the host's previous attributes, therefore they can wield weapons, and drive and board enemy vehicles. However, Infection Forms do not require their hosts to still be alive for infection. Even dead hosts are suitable for conversion into a Combat Form, reanimating them after infecting them; though the brain tissue remains dead, the victim's biomass and calcium reserves are sufficient to warrant infection.

In the initial stage of a Flood outbreak, the Feral Stage, Combat Forms communicate using pheromones and have one instinctual behavior; to secure new hosts to strengthen the local controlling intelligence. Once a sufficient store of biomass is available the Flood enters the Coordinated Stage, and begins forming Pure Form Flood, with the Combat Forms being used either as defensive units or calcium/biomass reserves. Infected hosts are rapidly digested while being converted, which leaves the host severely ravaged and decayed, much like a corpse that had been exhumed a few weeks after its burial. Flood infection is a rapid and efficient biological process, as it can take under a minute in certain cases.

Stalker[]

The Flood Stalker Form is a crustacean-like Flood Pure Form that specializes in stealth and agility. It is apparently made from the re-casted bones of dead enemies. It will frequently mutate into either a Ranged Form or a Tank Form when the need arises. They are able to crawl on walls and ceilings with ease, and are capable of making enormous jumps much like combat forms. Stalker forms are very weak; to make up for their fragility they are incredibly fast and agile.

Ranged[]

The Flood Ranged Form is a type of Flood Pure Form. It is formed when a Stalker Form is damaged or chooses to mount itself in a stationary position either on the walls, ceiling, or, with less frequency, on the ground. It has a mouth-like protrusion that opens up to reveal a living missile platform of regenerating spikes. These spikes will relentlessly pelt the enemy. When fired upon these forms will curl up to shield their heads, their weak point.

Tank[]

Tank Forms are slow in comparison to the other Combat Forms but they make up for it with relative resilience and their devastating melee attack, as they are unable to wield weapons with their arms that are shaped into hardened spikes (as opposed to whip-like tentacles exhibited by other Combat Forms). However slow, they can run on all fours for a short period, allowing a short burst of speed to overtake a target. On occasion Tank Forms eject Infection Forms from their 'mouth' as if regurgitating them (not explosively like the Flood Carrier Forms) as a form of short ranged attack. They are mutated from the Stalker Form.

Gravemind[]

The Gravemind (Inferi Sententia, meaning "Thinking Dead"), is the final stage in the life cycle of the Flood and is the leading intelligence of the Flood. It is a near-omniscient creature with complete control over all Flood forms. A Gravemind starts out as a Proto-Gravemind -- a Flood form created by merging the bodies and biomass of numerous sentient life forms; some Flood forms may also be repurposed and merged into the Proto-Gravemind.

After a Proto-Gravemind has been created, nearby Combat Forms will continue to supply it with fresh bodies, allowing it to accumulate mass, increase in size, and gain more memories and intelligence from consumed hosts. Eventually, the Proto-Gravemind reaches a certain critical mass and becomes self-aware—a Gravemind. This critical mass tends to be made up of thousands of bodies if using human-sized bodies as a measuring unit.