40K LORE: Tyranid Planetary Assimilation

Today Loremasters we study the dark fate of worlds lost to the Tyranid Hivefleets.

In the process of assimilating a planet’s biological and inorganic materials, the most important stage is the location of a suitable target. One method by which they accomplish this is the spectral analysis of distant stars to determine their likelihood of supporting life. However, the fastest and most common method is the use of vanguard organisms, millions of which range hundreds of light-years ahead of each Hive Fleet, investigating each star system they encounter for signs of life. Once a suitable world has been detected, these bio-vessels spawn infiltrator-organisms, such as Lictors, Genestealers, or specialized Gaunt strains, and launch them onto the world via Mycetic Spores. Once inserted, these organisms will seek out all life and target those of a highly-organized nature, such as humans, restricting themselves to lone targets so as to avoid revealing their presence. Genestealers in particular will seek to infiltrate communities and create cults, not only to signal the planet is ripe for consumption but to weaken its defenses against the Hive Fleet’s arrival.

As the psychic beacon of the infiltrator-organisms flourishes, indicating a rich feeding ground, so does the Hive Fleet home in on it, in the process cutting off all interstellar communications as the Shadow in the Warp blankets the target system. Upon arrival to the planet, the Hive Fleet will disperse within the planet’s upper atmosphere and begin launching millions upon millions of Mycetic Spores. Many will contain Tyranid warriors of various strains, from Rippers to Bio-Titans, and so come in a multitude of sizes. Others will deliver zoomorphic symbiotes and parasites, which target and mutate the planet’s flora at a rapid rate. Within hours verdant forests are replaced with highly-aggressive alien vegetation, including Capillary Towers, which begins the process of transforming the planet’s atmosphere into a hothouse, turning the sky a sickly red and raising temperatures at an accelerating rate. Other spores are nothing more than giant cyst-bombs, filled with viral and poisonous organisms which burst over population centers, killing millions of people in the opening hours of the attack. Each one will cover an area many hundreds of meters across with acidic digestive bile, starting the process of future ingestion.

After the initial attack, vast swarms of flying Gargoyles will herd the native population into the path of fast-moving hordes of Gaunts to be viciously slaughtered. The defenders, often underestimating the Tyranids’ intelligence, make fighting retreats to buy themselves time to regroup from the onslaught, only to be encircled and destroyed as it becomes apparent they were merely herded into prepared killing grounds. These last pockets of resistance will become the targets of larger Tyranid species, from Warriors to Carnifexes and Bio-Titans, which eradicate the defenders with sheer offensive power.

With resistance ended, consumption of the planet’s resources begins. Bacterial agents and vast tracts of feeder organisms, pupated from the carcasses of native life forms, ravage the landscape of every ounce of biological matter before being collected into Reclamation Pools, where the matter is rendered into a thick, nutrient-rich gruel. This includes all mutated plant-life, which has finished altering the atmosphere into an oxygen-rich environment, and any infested organisms, who march blank-faced into pools’ depths to be consumed by the Hive Fleet. As the digestion pools swell, the Hive Fleet’s ships cluster in low orbit as vast capillary towers emerge to link with proboscis-like feeding tubes and pump the biomass into them. The final stage of the harvest is the consumption of the world’s atmosphere and seas, with vast drone-ship haulers descending to low orbit and sucking up every useful element left. Eventually the Hive Fleet will depart, having left the world a desolate airless rock stripped down to the molecular level, to begin the consumption process on another world.

Sample Assimilation of Dalki-Prime

Planetary Assimilation
Day Description
00 Initial mycetic spores are dropped, generally containing Lictors or Genestealers. Infiltration force led by a synapse creature of some kind; reproduction of Tyranid creatures likely begins immediately.
09 By day 9, Tyranids will have expanded to around 200 km from the drop point, and will likely present a significant threat to planetary defence and resident Imperial Guardforces.
13 Tyranids will have expanded to 700 km from the drop point; may begin infesting local water sources.
37 Tyranids control area within 2000 km radius of the drop point; basolithic infestation to 5000 km radius.
48 Tyranid population growth skyrockets, with population doubling approximately every 2.5 days.
50 Main Hive Fleet arrives, craft generally numbering around 1.5 billion. Psychic contact with planet is cut off by the shadow of the Hive Mind. Any attempts to escape are quickly stopped by the Hive Fleet.
51 Primary consumption of bio-mass begins (resistance has generally been eliminated by day 51). Brood ships land, releasing Ripper swarms, which consume all remaining organic material and depositing them at the reclamation pools. Capillary Towers(and the Brood ships) send the material into orbit.
80 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. Lack of oceans causes plate tectonic shifts, dramatically increasing volcanic activity. Upon completion, the Hive Fleet move out of the system in search of fresh prey.
100 The Imperial Navy arrives in response to the distress call to find the world lifeless.


Learn More of the Tyranids

~Offer up prayers to the Emperor for those lost to the Great Devourer.

  • Sonic tooth

    horrible creatures!!

    • Jabberwokk

      pfft I call it natural selection. *slurp* And a good day at work.

  • Angus MacKenzie

    “Basolithic infestation”? Tyranids have been my army since I started 15 years ago. I can’t remember ever reading that they infest specifically plutonic igneous rock.

    So they only go after the granites and diorites and such. What are about other rock types? Why not diversify, spread just a little at first to some thermally metamorphosed types like quartzite or marble? From there try out some sedimentary rock; nothing too fancy at first. Maybe limestone or sandstone. Can you imagine the horror of tyranids infesting a planet’s strata of greywacke or dolomite? Truly terrible even to contemplate!!

    • euansmith


    • Richard Mitchell

      Scientist and science ruin science fiction.

  • Rafał Pytlak

    Imperial Guard anwsers the call in just 100 days? That’s actually hella quick for the standards of the stagnant and bureaucratic Imperium of Man. Must have been an outpost nearby…

    • Richard Mitchell

      Probably the moon of the planet that was being attacked!

  • Drpx

    Damn that art. Reminder of 40k’s Lovecraft days.