This article contains PROMOTIONS! Don't say we didn't warn you.
This article or section is EXTRA heretical. Prepare to be purged.
The Tyranids (often shortened to simply 'nids) are a race of extragalactic "alien locusts" in Warhammer 40k that seemingly exist only to devour biomass and grow their numbers. They are extremely adaptable, and frequently genetically engineer traits and characteristics from the unfortunates they devour into their own species in order to improve their combat effectiveness; as a result, they are constantly evolving and becoming more dangerous. The Tyranids are most commonly seen in the galaxy in the form of Hive Fleets, large collections of spacefaring organisms that are capable of transporting and growing the smaller strains of the species, as they travel from world to world, attacking them and consuming all the available resources of the planet.
The Nids are connected and controlled by the extremely powerful and near godlike HIVE MIND. The hive mind is the gestalt collective consciousness of the entire Tyranid race, a psychic embodiment of the Tyranid instincts and racial imperatives to devour and destroy.This superconsciousness allows their forces and armies to move with a unity of purpose and cohesion that makes them extremely dangerous. The individual intelligence of different strains of the species is variable, however, and many of the smaller species lack the psychic power to communicate over long distances, and so the swarm relies on larger so-called "synapse creatures" to act as relays and nodes in the psychic communication network (If the Hive Mind is the Internet (Internid), then synapse creatures are ISPs (ISynaPse) and routers (got nothing)). Outside of the range of a synapse creature such as a Tyranid Warrior or Hive Tyrant, smaller varieties such as those found within the Gaunt genus revert to animalistic behaviour. However, certain strains, such as the Genestealer or the Lictor, are intended to spend long periods of time beyond the reach of the Hive Mind, and are consequently considerably more intelligent and autonomous than other varieties.
The normal Tyranid modus operandi is to locate a delicious looking planet, usually by following the psychic emanations of vanguard organisms like the Genestealers, who are sent ahead as scouts to infiltrate and form cults while obtaining genetic information about the local species (hence the name Gene-stealer), drawing the fleet towards a viable target. It is also known that Tyranids are attracted like moths to concentrated sources of psionic energy such as the Astronomicon. The Tyranids are capable of non-Warp-based FTL travel, which they achieve by using gravity to manipulate spacetime and travel extremely quickly towards large gravity wells such as stars; once they are relatively close, they must rely on STL travel to close the gap with their target, but the power of the Hive Mind is such that it casts a stifling influence over the Warp in the area, rendering warp-based travel and communication almost impossible. Hence it is that a world that finds itself the target of a hive fleet is unable to call for help or receive reinforcements by the time it realises the Hive Fleet is there. Once they reach the world, vast swarms of creatures flood down to the surface to overwhelm all resistance and consume the planet's population and resources in a manner reminiscent of a Korean StarCraft champion performing the devastating "Zerg Rush"
(Note that the Zerg were based on Tyranids, which in turn were based on Starship Troopers, Alien and such, and in turn were based on real-life hive insects such as bees and the mantis). (This is a topic of some debate with no conclusive evidence to support any of these claims)(No it isn't, and what do you mea evidence? It's pretty fucking obvious) In the later stages of the invasion, the Fleet manipulates the planet's environment and seeds it with aggressive plant life that grows extremely rapidly and assimilate nigh-on all the nutrition available in the planet's biosphere, which is then consumed by the creatures of the swarm and massive feeding tentacles dropped by Tyranid bio-ships in low orbit, and hence conveyed to the Hive Fleet as a whole.
This makes the Tyranids very dangerous foes to fight; even the Imperial Guard and Orks will find it impossible to beat in a war of attrition, as individual losses are meaningless to them. As long as they are able to recover the biomass of their slain, it is simply recycled into new warriors and ships. It's worth noting that going against technological species results in fewer and fewer recycled biomass, so a Hive assaulting a high-tech heavily fortified fortress loses some of its summary biomass bit-by-bit, but there are only few cases when Tyranids really bite off more than they can chew. Even a Hive Fleet that has taken terrible losses and forced to retreat may soon return to terrorise strong worlds, as capturing and consuming few poorly defended backwater planets is all that is required for them to replenish their forces. Even Hive Fleets considered defeated by the Imperium may still have splinter elements that survived and continue to infest worlds in the region. It is worth noting that, in the rare event that two different Tyranid fleets encounter each other, they are apt to attack each other. This is generally believed to be some sort of Darwinian selection mechanism to compare the competitiveness of the traits the individual fleets have absorbed, with the victorious fleet consuming the other, absorbing their best traits, and culturing a deadly hybrid with the best of both worlds.
So far, only fragments of Tyranid Hive Fleets have made it to this galaxy, and they were given monstrous names such as "Behemoth" and "Leviathan" and ate untold numbers of planets before finally destroyed or stalled. It's also known that these are merely scouting fleets for the unimaginably large swarm that has yet to arrive, still currently in transit from another galaxy (Imperial scholars suppose them to be either en route from a galaxy they successfully scoured of all life, or retreating from some force even nastier than they are). Noted Imperial scholars believe that the only possible plan that stands any chance against the arrival of this force involves giving a melta gun to everyone that has hands and praying to the God-Emperor for the best. They have been expected to arrive on Terra's doorstep any day now for years, being stalled by a force even more malicious then they are: GW's refusal to move the story foward.
And if they do expect the above to be retcon so that Leviathan is in fact the main force, as the above was coming form a crazed inquisitor.
Some fa/tg/uys masturbate furiously to anthropomorphized versions of Tyranids. These people are miserable deviants who must be consigned to the loving and understanding care of
a mental institution the local Commissariat. Equally as prevalent is the depiction of various Tyranid organisms engaging in lewd and disgustingly heretical acts with females (and the occasional male). Admittedly, this is not as much of a stretch of the imagination, what with how Genestealers infiltrate populations while their reproduction involves what is essentially "date rape" (i.e. hypnosis followed by injection of its DNA into unwilling victims). It doesn't help that the Tyranids have a unit called a "Dominatrix", and of course how their guns look and work like hentai tentacle-penises that ejaculate either virile swarms of flesh-eating diseases and phallic worms or steaming globs of malodorous acidic spunk. Only a matter of time before people imagine about Slaanesh corrupting Hive Ships.
 On the Table
 5th Edition
When the 5th edition Codex released, it was met with split opinions, as usual. Some were angry at how overpowered the army looked, citing the facts that the Tervigon could create more units out of thin air using "broken" special rules, that the anti-psyker powers were so broad, and that the Hive Guard and Zoanthropes were so good at tank hunting at a time when tanks were kings.
However, after some time passed, people who decried the cheesy aspects of the army faded from view as people began to realize the army only seemed cheesy on paper, and that, in truth, any cheese the army had was drowned in the army's drawbacks. The Termagants the Tervigon could spawn? Stats like a Guardsmen in close combat, but with half their weapon range and weaker armor. And to get Tervigons to the Troops slot from the HQ slot (where they were practically useless), you had to pay Guardsman prices for a unit of them. In other words, you had to use the "cheesy" special rule or they were overpriced into uselessness.
Then there were the special powers that supposedly buffed the army. Again, at a first glance, they looked broken. Certain upgrades allowed any unit within 6" of certain models to gain rules like Feel No Pain, Furious Charge, Poison, cover saves, and so on. It sounded like a serious boon, but it had a funny effect. Aside from the fact that most Tyranid models are too expensive unless you capitalize on the bubble-buffs, it also does a horrible thing to your freedom to play the army. Mainly, it forces players to keep all their units bunched up within 6" of a few key models, requiring them to spend the entire game in a rigid formation that can spell disaster for the army when broken. Tyranids already suffered from this problem somewhat due to their synapse rules, but the 6" range on the mandatory buffs only shortened the leash. Not to mention it also made blasts even worse for an army already vulnerable to them.
Tyranids do seriously lack effective long range support as well. While they possess some weapons capable of mincing infantry units, most things with a range over 12" come at a premium. With an army so focused on close combat this shouldn't be such a problem, but synapse and buff leashes actually make it a valid concern. Mainly, the short buff leash pressures a player into a castle formation, but the lack of medium and long ranged weaponry pressures the player to advance the entire castle towards the enemy, which has a way of creating chinks in the formation. And you can't just move a few key units - when a unit moves forward, the model providing the buffs has to follow them, and then the other units relying on the buffs have to follow the model providing the buffs; it just makes the army obscenely inflexible.
Tyranid monstrous creatures, their heavy support, also got drastically nerfed in the 5th edition update. 6th edition rules have mitigated it somewhat, but the supposedly heavy-hitters of the army have limited roles or schizophrenic weapons options. Like the Tyrannofex, for example: with a 2+ save and six wounds at a toughness of six, the damn thing is almost indestructible, but the weapons are short-ranged, and if you buy it an expensive long-range cannon to shoot at tanks, you can't change any of its other short-ranged weapons which are designed to kill infantry. You just can't quite kit your heavy support to do the things you specifically want.
Which brings us to the final problem: on top of mountains of tactical inflexibility, the Tyranids also suffer from the drawback of design inflexibility. Unlike Guardsmen or Space Marines, the Tyranids don't get a lot of options to change the way the army works. When you buy hormagaunts, you get them at face value - you can't equip them with frag grenades, give them pistols, add heavy weapons, or mess with their gear in any way. You can buy them the poison special rule if you want, or maybe the Furious Charge special rule, but those are your two choices. Almost the entire army is that way, which is vastly different than the way they worked in 4th edition. The Carnifex alone lost eighteen weapon and biomorph options between 4th and 5th edition and it doubled in points value. And with no upgrades taken! And for twenty points more, you can get a trygon. Which is better then the carnifex in almost every way. Cept looking good. It's possible that Tyranids are now the least adaptable army in the game.
The last kick in the teeth is that Tyranids are one of the more expensive armies to collect, requiring a larger number of models than most. Their HQ choices, short of the Tyranid Prime, are big monsters which run at prices edging nearer and nearer to $100 each. For the fact that most Tyranid armies will play exactly the same way, having all the same exploitable weaknesses and no unique wargear surprises, it's not a wonder that the army has seen a huge drop in sales since the release of their 5th edition codex. The shorter lesson to take from all this is, if you're thinking about beginning a 40k army, even with how expensive it's all gotten, Tyranids are not the best army to start with.
This now concludes the awesome part of all things Tyranid. If you look at the gallery below the Cutenids, you will require a mind scrubbing and be lobotomized into a servitor. No exceptions.
 6th Edition
WEEEEEEEEEEEEEE!! THE FAIL TRAIN HAS NO BRAKES!
UPDATE TIME: Tyranids are confirmed for getting a new Codex soon (announcement on 4 JAN 2014, street release date 11 JAN 2014). Now that it's out, it sadly more of the same so far and may in fact have nerfed them FURTHER. Though a few new units did get added, most of which weren't even mentioned since Chapter Approved 2001 (such as the Exocrine and the Haruspex), along with a new FMC called the Crone, also on the pplus side, rumour has it that carnifexes are going to be a fair bit cheaper, and can take almost any biomorph, and Flesh Hooks are back but only three units can have them.
...And virtually everything the Tyranids needed to stay competitive was either removed or nerfed to uselessness. On the downside, Tyranids no longer have Mycetic Spores, the Doom of Malan'tai, Ymgarl Genestealers or the Parasite of Mortrex (GW lost a pissing contest with Chapterhouse Studios, with the rather iffy ruling that GeeDubs didn't have the IP right to the models ChapterHouse was producing, and now they're taking it out on us because "fuck balance and competition" apparently). They even lost the ability to use psychic powers from the Biomancy table along with their Hive Mind powers being nerfed. Why GW thought that the most underpowered army needed even MORE nerfing will remain a mystery (But odds are that Cruddace had something to do with it). A perfect example of unnecessary nerfing is the tyranid prime; it was rarely fielded in 5th edition, and the 6th edition codex inexplicably increased its cost by over 56%. At any rate, it looks like the Tyranids will soon be joining the Sisters in GW Hell, rather ironic as they were once under the axe along with Squats. Keep in mind that GW stocks were already dropping due to the financial disasters that were 6th ed Apocalypse, Strong Hold Assault, and Escalation, but we're not kidding when we say, that, THE NEW CODEX WAS SO BAD THAT EVEN THEIR STOCKS PLUMMETED BY 23%! Meanwhile in Warhammer Fantasy there's 3 armies which are at least one edition behind in updates (with Dwarfs updated in Febuary 2014). Along with the announcement was plans to close many GW stores, including their headquarters in Germany... yeah, this might be the beginning of the end.
BUT NO! WE SHALL NO FAIL, IT IS THE ENEMY WHO WILL GET TASTED AND EATEN! Ahem, GeeDubs has released some Dataslate formations which allow you to
buff your Tyranid armies to make them quite competitive, ignore the force organisation chart to spam flying monstrous creatures and overwhelm an opponents anti air defenses because the flyer rules are an even larger catastrafuck than the tyranid codex. Expect discussions and rage about allowing these dataslates for tournaments.
 See Also
Thus far the Cutenids. From down here there be many promotions. All abandon hope ye who enter here.
This article contains PROMOTIONS! Don't say we didn't warn you.
I'd let her clean up my biomass, if you know what I mean.