An Ymgarl Genestealer

The Ymgarl Genestealers (Corporaptor ymgarli) are a variant of Tyranid Genestealers who were first encountered on the moons of Ymgarl in circa 500.M41, about 200 standard years before the Milky Way Galaxy was invaded by the Tyranid Hive Fleet Behemoth. They were the first Genestealers encountered by the forces of the Imperium of Man and were initially thought to be a new species of previously unknown intelligent xenos.

It was later discovered that they were just one variant of the standard Genestealers deployed as a servant bioform of the Tyranid hive fleets. Every attempt made by the Imperium to eradicate them has ended in abysmal failure and the usual wholesale butchery of those who made the attempt.

Genestealers are known to change over the generations. The different variations between broods can be quite marked, but the Ymgarl Genestealer is truly unique because it possesses the ability to alter its own flesh to react to incoming attacks or to change its colour like a chameleon so that it can blend into its surroundings and remain unseen until it escapes or attacks.

Its claw-tipped fingers can suddenly elongate and fuse together to form curved blades and barbed hooks or split apart into tentacles of sinewy alien flesh to slash or entangle those victims who try to escape. Under assault its chitinous carapaces can thicken and help its leathery hide absorb the energy of incoming melee or ranged assaults.

Some Imperial observers who have had contact with this creature and have reported this strain of Genestealer's ability to change the colour of their skins believe they do so to better go undetected in the darkness of night or other extreme light conditions.

But this extreme adaptability comes at a high price for this bioform. Ymgarl Genestealers must feed on large amounts of biomatter, and feed often. Ymgarl Genestealers' most distinctive feature is the mass of writhing tentacles that replaced the fanged mouth found on the standard strain of Genestealer which they use to pierce their victim's flesh to better feed upon the blood within -- this strain's only source of real nutrients.

Those Ymgarl Genestealers that cannot obtain adequate nourishment to feed their raging metabolisms in this way will be forced to enter a state of dormant hiberation or starve to death. Within this state they will wait until something living -- and filled with fresh blood -- comes to disturb their dreamless sleep.

The origins of the Ymgarl Genestealers remain a complete mystery to Imperial scholars, for they do not seem to have been a strain of bioform created by any of the hive fleets already known to have invaded Imperial space. It may be that they are the last survivors of a Tyranid reconnaissance of the galaxy before the arrival of Hive Fleet Behemoth.

Even stranger, whilst the survival instincts of the other Genestealer strains leads them to flee the oncoming arrival of their parent hive fleets, Ymgarl Genestealers actively seek them out, as if they hope to once again hear the comforting presence of the Hive Mind that has long been absent from their thoughts.

They spread across the galaxy searching for those inhabited planets that lie in the path of an approaching hive fleet. Once there they will lie dormant in hibernation until the Hive Mind reasserts contact with them and they can hunt alongside the rest of the Tyranid swarm. However, the Hive Mind has no desire to reabsorb their biomass or genetic legacies, lest their known instability spread throughout all of the bioforms in the hive fleet.

Once the target world has had all of its biomass devoured, the Ymgarl Genestealer brood is abandoned by the Hive Mind, forced once more to enter hibernation. Unfortunately, many Human starships often investigate the Dead Worlds left in the wake of a Tyranid attack.

They come to learn more about the horrific xenos, in the forlorn hope of discovering some miraculous survivors or as scavengers come to pick over whatever wealth may remain. These fools and idealists often leave the world with a far more deadly cargo hidden within their holds, ready to spread the cycle of death and terror anew.


A pack of Ymgarl Genestealers on the hunt.

As mentioned above, the Ymgarl Genestealers were at first not believed to be a part of the broader Tyranid species, but were instead thought to be xenos native to the moons of the world of Ymgarl first encountered by Imperial trade crews on merchant ships around 500.M41.

However, 200 standard years later, during the invasion of Hive Fleet Behemoth beginning in 745.M41, the Tyranids used Genestealers as shock troops and melee infantry in countless battles against the Imperium and the other intelligent peoples of the Milky Way Galaxy. The Magos Biologis of Mars spent many Terran years trying to classify the Tyranid artefacts and bioforms left behind on Macragge after the invasion of Hive Fleet Behemoth was stopped by the sacrifices of the Ultramarines.

Yet they could learn little about their origins from these remains. The only notable discovery had been that the Tyranids used the Genestealers as their shock troops. It had been believed that these xenos had spread across the galaxy onboard Imperial cargo barges and derelict space hulks.

Many of the Imperium's most violent encounters with Genestealers before the arrival of the Tyranids had been onboard infested space hulks and names of such hulks as the Sin of Damnation were forever synonymous with these deadly aliens.

The presence of Genestealers amongst the Tyranid bioforms proved that these previous assumptions concerning the Genestealers' independent origins had been false. Further genetic analysis confirmed that all Genestealers, even the tentacle-mouthed variant encountered amongst the moons of Ymgarl, were Tyranid bioforms.

In response to this news, the Space Marines of the Salamanders Chapter unleashed a xenocidal campaign to purge the moons of Ymgarl of the foul creatures and the Inquisitors of the Ordo Xenos intensified their search for any signs of new Genestealer infestations, but little else could be done to deal with the problem.

The question that continues to perplex Imperial scholars is whether the Ymgarl strain of Genestealers are the remainders of an unknown ancient hive fleet that entered the galaxy before Behemoth or whether there is more to the current Tyranid invasion than has yet become apparent.

No matter the answer to that question, the Ymgarl Genestealer strain was not completely destroyed by the Salamanders' efforts. They endure in the dark corners of the galaxy, always waiting for the chance to spread their infestation to new worlds and offer up yet another sacrifice for the Great Devourer.

The full truth about the Ymgarl strain has yet to be revealed.

Ordo Xenos Departmento Analyticus Data

Designation Ymgarl Genestealer

Common Name

Ghost, Leech, Sewerstalker
Species Name Corporaptor ymgarli
Role Infiltration
Average Height 1.9 metres
Average Weight

0.3 tonnes

Main Weaponry Claws and Tentacled Limbs
Secondary Weaponry Feeding Tentacles
Tertiary Weaponry Limited Shapeshifting and Camouflage
Threat Evaluation High


  • Codex: Tyranids (6th Edition) (Digital Edition), pg. 101
  • Codex: Tyranids (5th Edition), pp. 15, 61
  • Imperial Armour Volume Ten - The Badab War - Part Two, pg. 78
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