Thats the thing however.

The grox herds on the planet Snehta are docile. This is mainly because the flora on Snehta that the grox are fed or "graze" from has a natural calming fungi growing on it. The chemicals produced by the fungi react with teh groxes digestive tract and calm the critter down to a near comatosed state that renders the critter almost hpnotized, near lobotimized naturally, allowing grox herders to control the herd without fear of death and dismemberment.

This causes Snehta to be a very imporatnt supplier of grox meat and herds are regulary sent to the plant Arthals for "processing" in the "meat factories". When the planet of Snehta has several strange and unexplained grox vanishings and some mysterious grox mutilations and abnormalties (mutations) appear in their herds they put a self imposed quarantine on their grox exports, which causes the Administratum to look at them and go "eh, what gives mate?"

While the Inquisition is only slightly concerned (as the inquisitor in that system is more focused on a chaos cult on Arthals) the respond to the Administratum's pleas and requests by sending in a token cell of investigators to report their findings back. And the only reason he actually sends anyone is because 200 years ago Snehta was engulfed in near civil war when a mutant loving xeno worshipping cult emerged from the populace.

Nice idea Santiago!

I'm itching to spring some Nids or Stealers on my party (who have only encountered Necrons, Orks and Daemons so far from thr TT races), I might run something along these lines! Although I'm really keen to put them on a planet undergoing a full-blown Tyranid invasion after reading N0-1_H3r3's excellent Tyranid suppliment.

Grox-Stealer (x3)

I seem to remember that the Ymgarl Genestealers had a symbiotic relationship with a kind of slug-like creature, hence the mouthparts.

Ran the adventure and it went very well, aside from some cow mutilation and crop circle jokes. Players freaked when they saw the grox/gene stealer hybrid.

N0-1_H3r3 said:

What I have thought would be an interesting idea ever since I read about Kroot Shapers would be a situation where a genestealer cult landed on a Kroot inhabited world and took over a clan/tribe by either killing or genestealer inpregnating all of its shapers.  Once you had at least one or two shapers that were subverted then the rest of the kroot from their clan/tribe would rapidly (more so than human b/c humans need hybrids to be born, even w/ the fast gestation and growth rates of human genestealer hybrids the fact that existing adult kroot can incorporate others genetic material is faster) be assimilated. 

Of course the "pure" shapers of the rest of the kroot on the planet wouls see this as abomination.  And thuse begins the gene-war.  Who can assimilate the best and strongest fauna DNA the fastest?  Who can corrupt/assimilate the other side before the enemy out evolves them?  It would be a whole genetic arms race....