A Norn-Queen (also sometimes referred to as a Splicer-Beast) is the highly intelligent Tyranid bio-form that leads the great Tyranid swarms and directs the evolutionary paths they take as they adapt to each new environment or tactical need. They live upon massive Hive Ships in huge chambers at the centre of the Hive Fleet and ingest genetic materials. They then churn out through asexual reproduction all the countless types of bio-forms that make up the Tyranid Hive Fleet. All Tyranids have links back to a Norn-Queen, as the only way for Tyranids to reproduce is through this cloning technique. The Norn-Queens lead the Tyranid forces and direct the evolution of the Tyranid race. Although they are sentient beings unlike so many of the other Tyranid bio-forms, they spend their entire lives psychically arguing through the Hive Mind with their "sisters" about how the next swarm of Tyranids could be better adapted to the species' needs. The Norn-Queens are constantly producing Tyranid organisms, new bio-weapons, and starships from a planet's recently consumed bio-mass. The Norn-Queens control the fleet and send orders to Tyranid synapse creatures on a invaded planet. The synapse creatures then retransmit those orders to the lesser Tyranid bio-forms. The forces of the Imperium have encountered only a single Norn-Queen, during the Battle of Tarsis Ultra. A biological plague created by using a Lictor's DNA as the foundation for the pathogen was injected into the Norn-Queen by Captain Uriel Ventris of the Ultramarines 4th Company. This disrupted the Hive Mind's coherency and the Tyranid creatures reverted to overly aggressive, animalistic behaviours, turning upon one another in an orgy of cannibalism. This action also crippled a tendril of Hive Fleet Leviathan.
The Norn-Queens control the evolutionary course of the Tyranid swarm. Upon arrival at a new world they intend to strip of its biomass, the Tyranids disgorge the "Alpha" swarm of bio-forms.The Alpha swarm contains the genetic material of that particular Hive Fleet's ruling Norn-Queen. These creatures then relay telepathic information to the Norn-Queen on the new world's environmental conditions and battlefield requirements, which spawn the second and subsequent generations of Tyranid bio-forms, sometimes with tens of thousands of casualties in the collection of the data. Capture of an Alpha wave Tyranid bio-form can lead to the creation of a deadly neurotoxin which can directly affect the Norn-Queen, as was done by the Ultramarines during the invasion of Ultramar by Hive Fleet Behemoth. When a Norn-Queen is killed, the psychic backlash of its death in the Hive Mind causes nearby Tyranid Hive Ships to calve, creating more Norn-Queens within their interiors. This is an instinctual survival mechanism of the Tyranid species that is known as the Hydra Effect, and is the reason why when a Hive Fleet is defeated, it can quickly form splinter fleets that eventually become larger than the original.
A Tyranid Hive Fleet's Norn-Queens require a constant supply of genetic material and undifferentiated nutrient bio-mass (a slurry of organic and inorganic chemicals including minerals, proteins, nucleic acids and carbohydrates) in order to clone or genetically craft new Tyranid bio-forms. This bio-mass mainly consists of the slurry formed in Reclamation Pools on a target planet's surface that are pumped up into the orbiting Tyranid Hive Ships through massive Capillary Towers created by Tyranid bio-forms. Genetic material is also supplied directly to the Norn-Queen by other Tyranid bio-forms, such as the Coffin-Crawlers. This raw material is pumped into the great jaws that are located at the top of the Norn-Queen and then synthesised into a new bio-form design by the Queen's genetic shredder organs. The disassembled DNA structures form a gene-bank of millions of different genotypes that can be used to "assemble" a new organism using the biomolecular machinery of the Norn-Queen. This organic genetic engineering mechanism is very similar to a mammalian immune system in that it "remembers" the biochemical structure of every DNA sequence it has absorbed just as an immune system can biochemically "remember" every pathogen it has ever encountered.
These absorbed DNA sequences provide the raw material for splicing and mutation from which new Tyranid creatures are created. Once a type of bio-form has been engineered to meet a purpose determined by the Norn-Queen, more bio-forms of the same type can be cloned by all the other Norn-Queens of a given Hive Fleet. The Norn-Queens are capable of bringing forth new Tyranid bio-forms in a variety of different ways, each designed to ensure maximum reproductive efficiency. Most Tyranid bio-forms are born live as tiny, hideous larvae or as eggs that must be nurtured further before they hatch and rapidly grow into their mature, adult forms. Clusters of Tyranid eggs spill from the rows of ovipository orifices along a Norn-Queen's flanks, while nutrient fluid-filled depressions on the massive alien mother's upper surface writhe with maggot-like larvae. Fetal amniotic sacs for other bio-forms hang like ripe fruit from corded umbilicals, while huge Teleporter Worms burst from incubator pouches on the Norn-Queen's sides. The simplest Tyranid bio-forms often emerge in their fully mature state and then are directed to begin serving their expected purpose by the horde of small Tyranid worker bio-forms whose only purpose is to feed and maintain a Hive Fleet's Norn-Queens.
- Codex: Tyranids (2nd Edition)
- Codex: Tyranids (3rd Edition)
- Codex: Space Marines (5th Edition)
- Warriors of Ultramar (Novel) by Graham MacNeill
- White Dwarf 146 (UK), "Warriors of the Hives"