It is an immense psychic beacon powered by the life force of 10,000 psykers, calibrated

and projected across the galaxy by the Emperor himself.

Without it, navigating the Immaterium would be impossible and no human starship would

ever reach its intended destination.

So critical to the survival of mankind is the Astronomicon, that very few have stopped

to consider the consequences of shining such a powerful light into the darkness of the

universe.

Indeed, evidence has slowly begun to mount that the Astronomicon might have drawn the

attention of something lurking in the empty void between galaxies.

An unknowable consciousness of unprecedented scale, relentless in its advance, and leaving

only drained, dead worlds in its wake.

To the Imperium, this abomination is named for the first world it devoured, The Tyranids.

The true nature of the Tyranids defies any conventional classification.

It is not a single species or even genus, but instead most closely resembles an entire

space-faring ecosystem, composed of innumerable bioforms.

These can vary tremendously in their size, appearance and function, but remain only variations

on the same genetic theme.

Together they form a distinct collective superorganism, capable of travelling across the universe

in living armadas known as Hive Fleets.

These Hive Fleets systematically consume all biomatter in their path as a means to facilitate

their own rapid evolution and reproduction.

The diversity of Tyranid life present within these Hive Fleets can not be overstated.

At their core, are impossibly massive bio-ships, living creatures that function simultaneously

as starships rivalling even the mightiest battleships, and biological factories which

endlessly replicate millions of Tyranid organisms.

Hive Ships are escorted by countless other Tyranid organisms far too varied to be systematically

categorized.

Together, these fleets are so vast that they are often mistaken for Nebula when viewed

at a distance and can blot out entire stars upon their closer approach.

Every Hive Fleet encountered so far is driven by the same collective Hive Mind but each

exists as a separate force.

Their composite lifeforms can differ significantly in their appearance or exhibit different and

unique strategies for overcoming local resistance.

In several instances, different Hive Fleets have been observed competing with one another

for resources, lending credence to the idea that each fleet exists as its own separate

entity.

The truth of the relationship between Tyranid Hive Fleets is likely far more complex, perhaps

more akin to single cells within a living body rather than rival factions.

Within the bio-ships of each Hive Fleet are swarms of biomechanical creatures, produced

by the directive of the Hive Mind to adapt to whatever its current circumstances.

Tyranid matter is constantly reabsorbed into biomass reclamation pools to create new species,

or adapt existing ones to better suit the Hive Mind's immediate purpose.

This is made possible by their extraordinary rapid rate of evolution, the key to each Hive

Fleet's adaptability.

The same basic forms of life however can be found in every Hive Fleet.

Small, maggot-like creatures known informally as “Rippers” are perhaps the most common

species.

They are almost always present in great swarms, capable of overpowering and consuming creatures

many times their own size.

In certain instances, Rippers have been known to bury deep underground and metamorphosize

into more advanced bioforms.

In all likelihood, Rippers are an immature form of Tyranid life, and theoretically capable

of gestating into any other type of bioform when given the proper signals from the Hive

Mind.

What might be considered the standard infantry of Tyranid Hive Fleets are known as “Gaunts”

and divided into a multitude of subspecies.

Typically they posses large, scythe-like claws or a type of ranged bioweapon which fires

a grotesque form of living ammunition.

Some variants even posses wings, while others are designed to hunt in total darkness, or

any other type of environment.

Larger Tyranid life forms likewise exist to fulfill every conceivable need.

The Tyranicus Gladius, more commonly known as simply the Tyranid Warrior, serves as a

far more capable type of shock trooper.

Like its smaller brethren, it is highly adaptable to any battlefield condition.

Well over 200 variants have been observed so far and it is possibly the most versatile

of any Tyranid species yet encountered.

The Tyranid equivalent of a main battle tank is the Carnifex, a living battering ram impervious

to all but the most powerful weaponry.

While not as adaptable when compared to smaller bioforms, the Carnifex has nevertheless been

encountered as several different subspecies suited to either ranged or melee combat.

The largest Tyranid creatures deployed planetside are known as Bio-Titans.

These are colossal war engines which tower over the battlefield and have been known to

overcome even the Titan Legions of the Adeptus Mechanicus in direct combat.

Perhaps the most dangerous forms of Tyranid life are those specifically created from the

gene-stock of species living within the Milky Way.

Genetic materials harvested from the Orkoid race has purportedly been used to create a

type of living artillery, while Zoanthropes, perhaps the strangest and most bizarre of

Tyranid species, likely share at least some DNA with the enigmatic Eldar.

Only under threat of execution will servants of the Imperium speak of the suspected origins

of the Tyrant Guard.

These bioforms possess a tremendous resistance to injury of a kind only before seen in the

warriors of the Adeptus Astartes.

If this is accurate, it would mean that the Tyranid Hive mind has incorporated the DNA

of fallen Space Marine Chapters, and possess at least a portion of the genetic material

of the Emperor of Man--.

Attention Imperial citizen!

The transmission of unknown origin you have accessed has been deemed heretical by the

Order of His most Holy Inquisition.

You will remain at your terminal until such time the nature of your guilt has been determined.

Any attempt to resist Imperial authorities or again access restricted information will

result in the harshest method of execution.

May Imperial Justice account in all balance.

The Emperor pro--

Hive Tyrants act in a capacity that might, in other species, be reserved for field commanders

or warlords.

While larger and stronger than most other variants, the true value of these creatures

is their exceptional psychic abilities that allows in them a closer connection to the

Hive Mind.

Some believe Hive Tyrants act as a repository of the Hive Fleet's consciousness, meaning

they collectively embody the Hive Mind itself.

The relationship between the Hive Mind and individual Tyranid bioforms is only partially

understood.

All Tyranid creatures, from masses of Rippers to massive Hive Ships, possess a common psychic

bond.

This is known to the Imperium as the Synapse, and it enables the Tyranid swarms to think,

perceive, and act to their full potential within the greater super-organism.

Any level of coordination and control within a Hive Fleet is only possible through this

Synaptic Web, for its constituent lifeforms are too numerous and varied as to be completely

uncontrollable otherwise.

Generally, smaller, weaker Tyranid organisms are mindless, instinctive creatures, performing

their functions with no conscious oversight or committment by the Hive Mind.

Larger, more complex creatures by contrast are capable of advanced decision making appropriate

for their situation and require a larger, if still miniscule part of the Hive Mind's

distributed sentient awareness.

Within the tangled hierarchy of Tyranid fleets, swarms and broods exist a special type of

Synapse Creature whose slightly more advanced brain functions as a type of psychic hub.

Without these Synapse Creatures to relay and interpret the will of the Hive Mind, entire

swarms can quickly falter and more basic Tyranid bioforms might revert to animalistic behaviors.

The overpowering nature of the Hive Mind's psychic presence is a phenomenon known to

the Imperium as the Shadow in the Warp.

Whether deliberately projected by Hive Fleets or simply the by-product of the Hive Mind's

synaptic control, it manifests in most species as an all-encompassing feeling of dread and

hopelessness.

For highly psychic individuals or races, this effect is magnified even further often leading

to suicide or insanity.

The deadliest consequence of this anomaly however is the termination of any connection

to the Immaterium making psychic communications or the manifestation of psychic abilities

extremely difficult.

For many worlds reliant on psykers for interstellar communication, the Shadow in the Warp effectively

isolates them from the greater galaxy, preventing any means of escape or summoning reinforcements.

Even demons of Chaos manifested in the material realm by the Dark Gods wither in its presence,

and entire warp rifts have been sealed in the wake of a Tyranid swarm.

By the time the Shadow in the Warp is felt on a target world, it is almost certainly

already too late for the planet's population.

While this is usually the first sign of an imminent Tyranid invasion, it is probable

that specific bio-forms have already been present on the world for some time.

The earliest stages of a Tyranid infection are subtle.

A specialized vanguard, deployed in advance of the Hive Fleet will be active on a planet's

surface for months or perhaps even years.

The organisms deployed will have evolved abilities and behavior that focuses on concealment,

and will almost never seek out any type of combat.

Instead, they merely observe the native environment and relay their findings back to the Hive

Fleet.

Any attacks are limited to isolated wildlife, utilizing their genetic code to ensure that

the rest of the swarm will be able to function within the planet's unique biosphere.

The most insidious component of Tyranid reconnaissance are Genestealers.

These are among the most intelligent and independent creatures ever developed by the swarm, capable

of operating far from the controlling influence of the Hive Mind.

They clandestinely insert tiny embryonic Tyranid organisms into various hosts, which over time,

alter the victims genetic code and suppress their consciousness.

Often this is done over a period of generations with many not even realizing they have been

infected at all.

Eventually, affected individuals will become a type of slave to a localized version of

the Hive Mind, forming what have come to be known as Genestealer Cults.

These often manifest themselves as secret societies which worship the Tyranid race,

even while incapable of understanding its true nature or their role within it.

If a Genestealer cult has been successful, it will have thrown a targeted planet into

chaos and weakened local resistance.

The arrival of a Tyranid Hive Fleet within a star system marks the next stage of the

invasion.

With the Immaterium disrupted by the Shadow in the Warp, local starships can be safely

destroyed without the possibility of reinforcement or escape.

Once in orbit, Hive ships begin bombarding any inhabited planet with a rain of Mycetic

Spores.

These pods are filled with hostile mico-organisms which immediately begin preparing the planet's

atmosphere, oceans, soil, flora and fauna for absorption.

Complex organic molecules are broken down, and recreated in forms better suited for the

Tyranid species.

Other spores deploy more complex creatures, which quickly gather into swarms and descend

upon any organized resistance.

Using information obtained during their initial reconnaissance, they target strategic locations

and even local leadership.

Once Tyranid forces have established a foothold on a planet's surface, enormous Capillary

Towers are grown far behind the frontlines.

These towers concentrate the biomass that has already been absorbed, using it to either

breed additional organisms needed to pacify the rest of the planet, or to extend its tendrils

across entire continents.

Simultaneously, Capillary Towers begin processing the atmosphere, absorbing all insect life

and even airborne microbes.

When a planet has been fully subjugated, the remainder of it's biomass is relentlessly

devoured.

Capillary Towers crisscross the entire world, from miles into the atmosphere to the deepest

trenches of any oceans.

Once the last of the planet's defenders have been destroyed, the victorious Tyranid

swarms hurl themselves into digestive pools at the base of each Capillary Tower, their

bodies broken down so that they might be recycled into new creatures for future conquests.

Together with every molecule of organic matter or mineral wealth, they are transferred by

massive pumping organs into awaiting Hive ships.

Once this has been completed, the Hive Fleet moves on, leaving behind a planet stripped

of all life.

Tyran Primus was the first known Imperial world to be devoured in this manner, and it

was only through the dedication of a single Inquisitor that the full extent of the Tyranid

threat was revealed.

Three major Hive Fleets, Behemoth, Kraken and Leviathan have been encountered by the

Imperium since then, each bringing with it a truly staggering loss of life.

Yet there remain many smaller Tyranid fleets and splinters which have yet to be fully eradicated.

Hive Fleet Leviathan, the largest hive fleet ever encountered, remains the greatest danger.

Nearly half of the swarm was destroyed before it could threaten Holy Terra, while the remainder,

in a desperate gamble, was purposefully lured into conflict with the enormous Ork Empire

of Octarius.

Ork warbands and Tyranid swarms now clash there in an ever-escalating spiral of violence.

Orks from across the galaxy, even Ghazghkull Mag Uruk Thraka himself have arrived in the

Octarius Sector to battle Leviathan, growing bigger and stronger on their diet of conflict,

but every Ork devoured gives more biomass to the growing Tyranid swarm.