Tyranid infantry units tend to be fast, hard-hitting, but frail. They also have low point values, meaning Tyranid armies in play tend to be large. Tyranids have the most powerful counter-measures against enemies with psychic powers: many Tyranid units possess the "Shadow in the Warp" trait, which makes it harder for nearby enemy psykers to use their powers.
Genestealers are a sub-species of the Tyranid race, and while they can be played as part of a Tyranid army, they can also be played as a separate army in their own right. This genestealer army has human-genestealer hybrids, who to varying degrees resemble humans. Some hybrids look perfectly human, and therefore a player can integrate Imperial Guard units into a genestealer army, passing them off as human-genestealer hybrids.
Games Workshop has introduced three main hive fleets; Behemoth and Kraken, which have been both defeated, and Leviathan, which is one of the current threats to the known galaxy. The 8th edition Codex has also introduced a number of smaller hive fleets and splinter fleets, such as Hydra and Gorgon, among a number of others, such as Hive Fleets Jormungandr, Colossus, Tiamet, Ouroboros, Dagon, and Kronos. There are many other Tyranid hive fleets that have been destroyed or are still emerging. It is noted that these names are given by the scholars of the Imperium, rather than the Tyranids themselves. In fact, there is no evidence in the fiction that Tyranids have language or civilization, at least not as understood by other species native to the Milky Way. In many stories, they communicate with a complex array of insectoid clicking and buzzing noises, as well as reptilian roars, growls, and hissing sounds. Tyranids are thought to communicate primarily via a strong synaptic link to the so-called Hive Mind.
Tyranids were first mentioned in the 1987 rulebook Warhammer 40,000: Rogue Trader under the heading Tyranids and the Hive Fleets, and were illustrated in a form not too different from that of Gaunts.[2]
The first Tyranids used conventional, non-biological equipment such as lasguns and flak armor (although the rulebook stated that these represented organic equipment with similar capabilities).[3] The principal unit available to the Tyranids was the Zoat, a centaur-like creature enslaved to fight on the behalf of their Tyranid masters. In 2020 Zoats were made a part of the setting again, in the Blackstone Fortress campaign.
Genestealers were first introduced in the board game Space Hulk published in 1989, being heavily influenced by the xenomorphs depicted in the Alien franchise, which was very different from their original conception in an entry of the "Aliens and monsters" section of the first edition of Warhammer 40,000 (the "WH40K - Rogue Trader" manual). Since the 1990s, subsequent games like Warhammer 40,000 and Epic have absorbed Genestealer as part of the overall Tyranid army where they serve as the shock troops, although their origins are not related to any other Tyranid broods. A force composed purely of Genestealers can still be fielded as a sub-type of the Tyranid army, in what is known as a Genestealer Cult. The Cult is described in the in-game background as an infiltration force that weakens a target planet, infecting the local population and causing civil unrest in advance of the arrival of the main Tyranid hive fleet.
