The Parasite of Mortrex is a bat-winged Tyranid monster that plants Ripper parasites inside living victims, which then eat their way out. It’s one of the most infamous unique Tyranids, and it’s been a tabletop terror since it first appeared in the 5th edition codex.
What the parasite of Mortrex actually is
It’s a Tyranid organism roughly the size of a Warrior, with leathery wings and a barbed tail tipped in a hollow tube like a snake’s fang. That tail is an ovipositor: it injects still-living prey with Ripper parasites.
The Ripper embryos mature fast. Sometimes within hours, sometimes within a few heartbeats, they chew their way out from the inside. Every victim becomes a fresh swarm.
The fall of Mortrex
Imperial forces first met it on Mortrex, a fortress world in the Ultima Segmentum. Guard defences held the Tyranid invasion for nine days. On the tenth, the Parasite struck.
Each kill spawned more Rippers, and soon only armoured units would leave the walls. Even tanks couldn’t hold against the sheer numbers. Two weeks later the planet was overrun. One transmission escaped, warning the Imperium about the creature, and it hasn’t been seen since.
On the tabletop
It’s not a towering MONSTER, but it’s fast and sneaky. A 16″ move and the FLY keyword make it hard to pin down, and its Shadow Hunter ability penalises enemy hit rolls against it, even blocking re-rolls from characters like the Autarch.
It also carries the SYNAPSE keyword, so it buffs nearby swarms. Its Synaptic Imperative, Swift Onslaught, lets friendly critters surge further when piling in and consolidating. The Parasitic Infection rule is its signature trick, spawning Ripper bases from the foes it kills.
The INFANTRY keyword lets it hide in cover for a save bonus, then fly over the same terrain. Ripper Swarms got a boost too, with the Burrow and Squirm ability improving their saves in light cover.
- Moves 16″ with FLY, so it’s very hard to catch.
- Shadow Hunter makes it tough to hit and shuts down re-rolls.
- SYNAPSE keyword and Swift Onslaught buff nearby swarms.
- Parasitic Infection spawns Ripper Swarms from slain enemies.
Where it sits in Tyranid lore
It’s classed as a unique Tyranid, alongside names like the Swarmlord, Deathleaper, Old One Eye, and the Red Terror. These are one-off organisms rather than mass-produced bioforms, each with its own legend.
It also fits the wider Tyranid pattern of planetary assault: a single specialised organism appears, wrecks the defenders’ plans, and the swarm follows. On Mortrex, that’s exactly what happened.
Key facts
- It’s a bat-winged Tyranid about the size of a Warrior.
- Its tail is a hollow ovipositor that injects living hosts with Ripper parasites.
- First seen on the fortress world of Mortrex in the Ultima Segmentum, around the 900s of M41.
- The planet fell in two weeks, and the Parasite hasn’t been sighted since.
- It’s counted among the unique Tyranids, like the Swarmlord and Old One Eye.
- On the tabletop it has FLY, a 16″ move, SYNAPSE, and the Parasitic Infection rule.
FAQ
What does the Parasite of Mortrex do?
It implants living victims with Ripper parasites using its barbed tail. The parasites mature inside the host within hours or even heartbeats, then devour them from the inside out.
Is the Parasite of Mortrex still alive in the lore?
As far as Imperial records go, it hasn’t been sighted since Mortrex. One warning transmission got out before the planet fell, and that’s the last confirmed report.
What’s the Parasite of Mortrex’s tabletop role?
It’s a fast, sneaky support piece. It moves 16″, flies, buffs nearby swarms through SYNAPSE, and spawns Ripper Swarms from enemies it kills.