Tyranids

The Tyranids are a species of terrible xenos that is actually a space-faring ecosystem dedicated solely to its own propagation and evolutionary advancement. The Tyranids collectively form a monstrous superorganism that travels the universe in their great Hive Fleets of biomechanical Hive Ships, systematically consuming all other biomatter to enable its own rapid evolution and reproduction. All Tyranid organisms are Synaptic (psychically-reactive), and each Tyranid creature within a Hive Fleet shares in a communal Hive Mind, granting the ability for trillions of beings to communicate and organize instantaneously on a staggering scale.

The mentality of the Tyranid approach to warfare can be described with the phrase "quantity has a quality all its own". From the "lowly" Ripper, to the deadly Hive Tyrant and beyond, the signature of the Tyranid force is that they overwhelm their foes with sheer numbers, reproducing massive numbers of highly virulent organisms in record time from the biochemical soup that they derive from the biospheres of the worlds that they consume. The components of a Tyranid Hive Fleet travel almost exclusively in large groups known as swarms that possess specialized biomechanical creatures for destroying and consuming a wide variety of prey life forms. Tyranids have evolved sophisticated methods for facilitating genetic transfer across species boundaries. As a result, a significant goal of any Tyranid invasion is acquisition of useful new biological traits from other lifeforms. These are used by the Hive Mind to enhance the Tyranids' effectiveness in consuming new worlds to gain more of the necessary organic raw materials for further reproduction. All Tyranids are reproduced by a single, highly intelligent female bioform known as a Norn-Queen. A Hive Fleet's Norn-Queens are the most important Tyranids within the fleet, for if they are injured or killed the Tyranids cannot reproduce their numbers from the captured bio-mass. As a result, Norn-Queens can be found only at the heart of the largest and most-well defended Tyranid Hive Ships.

The Tyranids were initially described in the 1st Edition of Warhammer 40,000 (Rogue Trader), with their basic form not too different from that used today. Their only additional troop type was an enslaved race, the Zoat. At that time they were not an emphasized race in the Warhammer 40,000 universe. In later editions they became a playable race in their own right, and it was revealed that the Genestealers (first popularized in Space Hulk) were in fact part of the advance reconnaissance element of the main Tyranid Hive Fleets. The Tyranids bear many similarities to the xenomorphs from the Aliens movie series, such as their hive mentality and the appearances of some of the creatures.

Xenology
The Tyranids are actually an extragalactic species, born somewhere beyond the void that separates the galaxies of the Local Group. Tyranid Hive Fleets travel through space by using gigantic, organisms genetically engineered to travel through a vacuum known as Hive Ships, which move in groups which can be likened to very large locust swarms. Typically, Tyranid Hive Fleets move in ad hoc formations known as Tendrils, migrating to nearby inhabited planets after consuming all the biological and organic material on a recently invaded planet and breeding, often reproducing many times their original number. Hive Fleets travel with superluminal speed, though they never enter the Warp. Instead, by using the specialized psychic power of the a selectively evolved Hive Ship, they manipulate the gravity fields of star system to achieve faster-than-light travel. The massive Warp presence of the Tyranid Hive Mind, however, manifests itself in that realm through the Shadow in the Warp phenomenon. The current collection of Tyranid Hive Fleets have migrated to the Milky Way Galaxy, presumably after overpopulating or overfeeding in other nearby galaxies of the Local Group. Given that each Tyranid Hive Fleet has approached the Milky Way from a different direction, this may imply that the Tyranids have consumed a disturbingly large number of nearby galaxies.

Tyranid Hive Fleets consist of millions of biomechanical craft, each serving as host to an untold number of symbiotic organisms. These creatures evolve and spawn from a variety of geno-organisms in the ships' reproductive chambers. All these creatures are born to service the ship, and the ship in turn exists only to service the needs of the Hive Fleet.

Whereas other armies like those of the Imperium and the Tau fight for conquest or self-defence, and the Forces of Chaos and the Ork clans battle merely for the chance to wreak violence and havoc, the Tyranid Hive Fleets are driven by the will of the Hive Mind, which itself is motivated by the most ineradicable instinct inherent to all lifeforms - reproduction, and through reproduction and the acquisition of new genetic traits, evolution to a better adapted form.

A fully mobilized Tyranid Hive Fleet strikes shock, awe, and terror into even the most stalwart of humanity's defenders. Even when the xenos threat is eliminated (at great cost), it will not be long before another Tyranid migration emerges to take advantage of the situation. This is what makes the Tyranid species such a threat: it is an evolved metapredator capable of out-producing, out-consuming, and out-lasting all other species it encounters, having done so on a disquietingly unknowable number of prior occasions across a vast swathe of intergalactic space.

The Super-Organism
All Tyranids possess a common psychic bond, known as the Synapse. This bond enables the Tyranid swarms to think, perceive, and act as a single great super-organism, providing nearly seamless co-ordination and control within a Tyranid invasion force so numerous and extensive as to be completely uncontrollable otherwise.

From the smallest feeder organisms, to the microbes that decompose new biomass; from the sessile and rooted flora-like forms, to the huge tendril-like shoals of the Hive Fleets, every Tyranid organism has a place within the will of the Hive Mind. The lesser and smaller creatures are mindless and instinctive animals, plants and bacteria, performing functions with no conscious oversight or commitment, while larger and more complex creatures can make decisions appropriate to the situation and form an integral if minuscule part of the Hive Mind's distributed sentient awareness.

Synaptic Web
Functioning in perfect unison, coordinated by powerful psychic imperatives transmitted through the Tyranid communal sentience that is the Hive Mind, Tyranid fleets, swarms, and broods do not have a singular command structure, but rather form a synaptic web of psychic influence and feedback. Situated within this tangled web are specialised Synapse Creatures whose slightly more advanced brains function as psychic routers, buses, and hubs, co-ordinating and policing the riotous cacophony of the collective brain power of a mass organism that is sometimes larger than most planets. Without the localised control provided by these organisms, the swarm can quickly falter, and some Tyranid creatures may revert to animalistic behaviors, when individual will and situational instincts come into conflict. Often swarms will subdivide into smaller packs of creatures still capable of consensual behavior among themselves. The Synapse Creatures that channel the commands of the Hive Mind are mostly, if not all, potent individual psykers. How any of this is done without drawing the attention of countless daemons of Chaos or the other psychic predatory entities of the Warp into the midst of the Tyranid swarm is unknown and possibly unknowable to the humans of the Imperium.

History
The Tyranids first appeared in the Eastern Fringes of the galaxy in the late 41st Millennium, emerging from the intergalactic space of the Local Group of galaxies, their Hve Mind drawn by the beacon of the Astronomicon transmitted by the Emperor's presence in the Warp from Terra. First contact with the Tyranids for the Imperium of Man was a Tyranid attack on a moon called Tyran, and from there Hive Fleet Behemoth continued directly towards the center of the galaxy, consuming all worlds in its path. The Tyranids were defeated, barely, by the efforts of the Ultramarines Chapter of the Space Marines at the Battle of Macragge, although the Ultramarines suffered devastating losses.

Two centuries later, the Tyranids returned to the galaxy with Hive Fleet Kraken which, instead of throwing one mass of troops against the Imperium, split into countless smaller fleets, each small fleet enveloping whole star systems before reinforcements could arrive. The brunt of this new attack was borne by the Space Marine Chapters known as the Scythes of the Emperor and the Lamenters; the former Chapter was almost completely destroyed. Though the backbone of the Hive Fleet was broken by its defeats at the Battle of Ichar IV and at the Eldar Craftworld Iyanden, the cost to the Imperium was still great.

Only a few years later, Hive Fleet Leviathan unexpectedly appeared from "below" the plane of the galaxy (on the Z axis of the galaxy) and attacked from two points, cutting off large portions of the galaxy from reinforcements. Just as it seemed the defenses of the Segmentum Solar and perhaps Terra itself would be tested, the Tyranids were distracted by being deflected into the star system of a powerful Ork empire. While the Orks are managing to stall the main Tyranid Hive Fleet's advance, they are likely to reemerge from these battles, victorious and stronger than ever after having absorbed potent Orkoid genetic material into their own genome pool.

Commanders

 * Hive Tyrant
 * The Swarmlord
 * Dagon Overlord
 * Tervigon
 * Tyranid Warrior Prime
 * The Parasite of Mortrex

Elites

 * Hive Guard Brood
 * Lictor Brood
 * Deathleaper
 * Venomthrope Brood
 * Zoanthrope Brood
 * Doom of Malan'Tai
 * Pyrovore Brood
 * Ymgarl Genestealer Brood

Troops

 * Tyranid Warrior Brood
 * Genestealer Brood
 * Broodlord
 * Termagant Brood
 * Hormagaunt Brood
 * Ripper Swarm Brood

Fast Attacks

 * Ravener Brood
 * Sky-slasher Swarm
 * Gargoyle Brood
 * Harpy
 * Spore Mine Cluster
 * Mycetic Spore

Heavy Support

 * Carnifex Brood
 * Old One Eye
 * Biovore Brood
 * Trygon
 * Mawloc
 * Tyrannofex
 * other Bio-Titans

Organic War Machines
The Tyranids do not build their starships and weapons from metal and plastic like the other intelligent races of the Milky Way Galaxy; instead, they use gene-splicing and bioengineering to grow them from the organic biomatter harvested from the planets they consume. Every weapon, gland and projectile used in their armies is a bioengineered Tyranid organism in its own right, from the spores polluting the atmosphere, to the grotesque spires that burst from the tortured ground during an invasion.

Tyranid Combat Doctrine
Tyranids often attempt to first conquer a planet through subterfuge and infiltration. Space Hulks and other derelict spacecraft are infested with Genestealers, which quickly familiarize themselves with the layout of their new home, then hibernate.

When the Hulk is eventually discovered by Imperial authorities, the Genestealers attack the exploration crew, sometimes killing some crew members, but always leaving at least one survivor who is implanted with a seed, a form of Genestealer reproductive virus that contains specially-engineered Tyranid DNA. This infestation is never fatal, but instead the virus' genetic material subtly alters the victim's DNA, producing in them a strong urge to mate created by the stimulation of the individual's sex hormones. The Genestealer DNA will be incorporated into the host's germ cells and so any child that results from this union will be a Genestealer Hybrid, which now has the complete loyalty of its parents through a psychic bond. The Hybrids continue to breed and multiply among the population of the host species, eventually forming a Genestealer Cult. As the Cult grows in numbers, it begins to spread its influence throughout the planet's political and social structure, placing its members in positions of power within the government and the military. At the same time, the Cult's Hybrid members begins to emit a collective psychic signal through the Warp that acts as a beacon for the approaching Tyranid Hive Fleet.

As the Tyranid Hive Fleet nears the doomed world, the Genestealer Cult, potentially numbering in the millions by this point, goes into action, instigating a worldwide rebellion with the goal of weakening the planet's defenses against the approaching Hive Fleet. The Hive Fleet will also seed the planet with Tyranid organisms, which will begin to biologically alter the planet's climate, surface and ecosystems to make it easier to consume. If the Hive Fleet is victorious, the fleet will descend to the planet, inhaling the atmosphere, drinking the seas, and basically consuming all organic biomass until nothing more than a lifeless ball of rock remains.

On the battlefield, Tyranid tactics are based around the notion of superior numbers, as they generally try to outnumber the enemy fifty to one. Tyranids overrun opposition in close combat, closing faster than most armies. They possess few ranged weapons, but their sheer numbers and close combat specialisation makes up for the slaughter if they are led by a capable commander.

Stages of Planetary Consumption
Generally, contact with the Tyranids occurs when a Hive Fleet invades a star system for the purpose of harvesting its inhabited worlds' biomass. A Hive Fleet contains an enormous number of Tyranids, and they are brought to bear against resistance in the most efficient manner possible. Below is a general outline of a typical Tyranid planetary assault (in particular, this data is collected from the Tyranid invasion of Dalki-Prime):


 * Day 01: Mycetic spores are dropped, mostly containing Lictors and Genestealers. As soon as they hit the ground, the reproduction of Tyranid creatures likely begins immediately.
 * Day 09: By now, the Tyranid infestation will have expanded to around 250 km around the drop point, and will likely present a significant threat to planetary defense force troopers and the resident Imperial Guard.
 * Day 13: Tyranids have expanded to 700 km from the drop point; some may begin infesting local water sources.
 * Day 37: Tyranids completely control the area within 2,000 km radius of the drop point and basolithic infestation has begun to reach a 5,000 km radius from the drop point of the first mycetic spores.
 * Day 48: Tyranid population growth becomes exponential, with population doubling approximately every 3 days.
 * Day 50: The main Hive Fleet arrives, with the number of Tyranid craft in the swarm generally numbering around 1.5 billion. All psychic contact with the planet through the Warp is cut off by the Warp shadow of the Hive Mind. Any attempts to escape are quickly stopped by the Hive Fleet. Any remaining surface life is eliminated by Gaunts.
 * Day 51: Primary consumption of planetary biomass begins (any sentient resistance has generally been eliminated by now). Brood ships land, releasing Ripper swarms, which consume all organic material (even the other Tyranids) and deposit it at the reclamation pools. Capillary towers (and the Brood ships) send the material into orbit for use by the Hive Fleet.
 * Day 80: Ripper swarms board the Brood ships and return to the Hive Fleet. The hive ships descend into the upper atmosphere and begin collecting it. Reduction in atmospheric pressure causes oceans to boil away, which are also collected so that their free water can beused by the fleet. The loss of ocean mass causes plate tectonic shifts, dramatically increasing volcanic activity across the victimized world. Upon completion, the Hive Fleet reenters the Warp, in search of fresh prey.
 * Day 100: The Imperial Navy arrives in response to the planet's original Astropathic distress call, only to find a destroyed, lifeless, uninhabitable planet.

Tyranid Species
Tyranids appear in a multitude of genera, and all have an extremely rapid rate of evolution directed by the Hive Mind, adapting to threats in direct response to their presence. Tyranid matter is constantly reabsorbed into biomass reclamation pools to create new species and adapt existing ones to suit the Hive Mind's immediate purpose.


 * Hive Tyrants are large and enormously strong Tyranids, who act as the leaders of the swarm and a synaptic conduit for the smaller creatures. They are highly psychic and highly mutable, and have a closer connection to the Hive Mind than most other genera of Tyranids. They are skilled at both close combat and ranged attack, more so than most other Tyranid organisms. Sometimes they are spawned with wings. Imperial Techno-Magi believe that Hive Tyrants are the repository of a Hive Fleet's collective consciousness, which means they completely embody the Hive Mind, yet their destruction does not in any way diminish its presence.
 * Broodlords are another Tyranid synaptic organism, regarded as the epitome of the Genestealer breed. The Broodlord is one of the first Genestealers to make planetfall on a victim world. They are devastating in combat and are specifically adept at infiltration on the battlefield to get closer to the enemy. They are very adaptable and highly intelligent. Broodlords are also the center of Genestealer Cults, and they coordinate the cult's attacks. If the Broodlord is killed, then one of the purestrain Genestealers will eventually evolve into a new Broodlord after a period of time.
 * Tyrant Guard are a special species of Tyranid spawned in small broods for the sole purpose of defending the Hive Tyrant. They are large, tough, and difficult to harm, and it is nearly impossible to surpass their defense. Tyrant Guard are completely blind, utterly controlled by the synapse creatures they protect. On occasion Carnifex also benefit from the Tyrant Guard's protection. Tyrant Guard are believed by some Adeptus Mechanicus Magi to contain the DNA of the defeated Space Marine Chapters, but the Imperium considers this blasphemy and denies its very likely possibility.
 * Tyranid Warriors are synaptic foot troops for the swarm. In between the size of a Hive Tyrant and a Gaunt, they serve as psychic resonators and assist in guiding the lesser Tyranid troops into battle. They are fast and powerful, with the capability to be strong at ranged combat or in close quarters in a similar fashion to the Hive Tyrant.
 * Lictors are large, deadly organisms bred for their stealthy qualities. A Lictor is basically chameleonic in nature, allowing it to blend with its surroundings to hunt and later kill its prey. Lictors are usually only seen when the Tyranids are springing a deadly ambush onto an unsuspecting army, unleashing a bio-engineered killing machine within their own ranks. They range ahead of the swarms, performing commando raids of sorts, and gathering information by devouring their victim's brains. The Lictors possess stealth and cunning of an unprecedented scale - to a point where they can best the famous Catachan fighters in jungle combat. Many Imperial Guard commanders have lost their troops in the shadows as they blink for a second; that is the terrifying undetectable Lictor at work.
 * Gaunts are the basic staple combat unit of a Tyranid swarm. They are smaller and less physically powerful than most other Tyranid organisms, but they are extraordinarily adaptable and always attack in large numbers. They are a fully mutable species, and some are grown with extra wings, adrenaline/venom sacs, and even bizarre biomechanical weaponized symbiotes, including the dreaded spike rifle.
 * Gargoyles are essentially winged variants of the Gaunt genus. They possess many similar traits, including a smaller size and physical prowess than most Tyranid organisms. Gargoyles retain most of the physical traits of Gaunts, however, and their lower legs have atrophied to little more than stumps. Like their cousin, the Gaunt, they are capable of being armed with a large host of biomechanical, symbiotic weaponry.
 * Rippers are small, snake-like organisms designed to devour biomatter so that new DNA and nutrients can be absorbed by the Hive ships. They are released in the final stage of a Tyranid invasion.
 * Genestealers are ferocious humanoid creatures, supposedly derived from human DNA, that are used as a vanguard to the Tyranid invasions of the Imperium. They infiltrate human societies, creating Genestealer Cults, as described under the tactics section above. They are also used as shock troops on the battlefield, where their sharp claws and instinctive close combat skills allow them to tear heavily armed opponents to shreds.
 * Carnifexes – originally known as screamer-killers – are huge, hulking, living battering rams, armed with a variety of biomechanical, symbiotic weaponry. Even stronger than the Hive Tyrants, they are used for assaulting fortified positions and as armor formations, such as during boarding actions. Carnifexes are the Tyranid equivalent of tanks or Space Marine Dreadnoughts - and the monstrous creatures can be mutated into a multitude of different sub-species, some designed for tank hunting, others built to produce acid and toxins ideal for anti-infantry combat.
 * Raveners appear to be related to both Rippers and Tyranid Warriors. These large beasts are designed for fast assaults against lighter enemies, and dig through the ground to perform surprise raids.
 * Zoanthropes are a type of psychic artillery, whose highly evolved brains swell out of proportion with their bodies. Through their use of psychic powers they can perform a number of roles on the battlefield. Some evidence points to later incarnations of Zoanthropes being improved by the Hive Mind's assimilation of Eldar DNA following the Hive Fleet Kraken Tyranid assault on the Craftworld Iyanden.
 * Biovores are sluggish, sessile creatures, whose only task is to grow and launch Spore Mines towards the enemy. The Spore Mines grow inside the Biovore's body, and are then hurled across the battlefield through a muscle spasm. Biovores are supposedly evolved from Orkish gene-stock.
 * Bio-Titans are enormous organisms, evolved as a response to other races' Titans and other super-heavy warmachines. They are (as of yet) the largest land-based Tyranid creatures encountered. They range from nine to thirty feet tall, and can single-talonedly take out an entire squad of Space Marines.
 * Norn-Queens are gargantuan organisms that are essentially biomechanical wombs that give birth to all of the other known Tyranid life forms. They can biochemically and genetically manipulate biomass in infinite ways to create new organisms to serve any function the Tyranid race requires. The Norn Queens are housed in huge rooms aboard the Hive Ships. Each room is hundreds of metres high, filled with a single Norn Queen.
 * Dominatrixs are the Norn-Queen's link to the Tyranid ground forces. They are huge monsters, almost as large as a Bio-Titan and the stronger, more psychically-powerful female Hive Tyrant. They are symbiotically fused with a smaller (Warrior-sized) entity which acts as a psychic, synaptic link to the linked Norn-Queen aboard her ship.
 * Trygons are powerful serpentine organisms that tunnel behind enemy lines. Towering over even a Carnifex, Trygons are one of the most powerful Tyranids breeds in existence. Trygons can also become synapse creatures to control other Tyranids. Trygons can lead a force of Tyranids known as a 'Tunnel Swarm'. This swarm is usually comprised of Lictors and Hormagaunts. The armour of a Trygon vibrates as it moves, thus creating a bio-electric current which can be released at will on a group of foes.
 * Mawlocs are a subspecies of the Trygon. They are worm-like and blind, though they are incredibly agile despite their size. Their short claws are not suited for close combat, rather to tunnel efficiently under the battlefield, although they are by no means defenseless. They prefer to swallow their prey whole to be digested alive for several days. Despite being blind, the Mawloc can gather information of the surface through pressure waves since they can travel through solid and fluid objects below ground. When a Mawloc begins to home in on the enemy, severe tremors errupt on the surface, which can tell the Mawloc where its prey is with more accuracy. If the sound is regular and rythmic, it is easier for the Mawloc to home in on. Even a heartbeat will tell it where its next meal is.
 * The Hive Guard are charged with protecting Tyranid structures and are capable of unleashing salvo after salvo of intense firepower. Essentially gun-beasts, they are heavily armoured in a shell-like carapace and have a body designed to be a stable firing platform for the massive impaler cannon bonded to their forelimbs. Physically linked to the shard-beasts that comprise the ammunition of their cannons, Hive Guard can target enemies with unerring accuracy - even those who they cannot see because they can receive sensory impressions from the shard bests in mid-flight.