The Innerwyrm is a Genestealer Cult that originally infested the abattoir Agri-world of Fleishgate. A lynchpin planet that provides the meat of grox, grontock and bovian to the Mawdlin System, Fleishgate has long been taken over by a Genestealer Cult, its primogenitor Purestrain Genestealer organism brought to the planet inside the guts of an immature Void Whale hewn apart for its meat.
The cultists take their inspiration from the arm-length intestinal parasites they find inside the guts of their livestock, for their hidden cult grows strong within the mass of Humanity's ignorant herd.
The use of the saw-spine wyrm-form as the symbol of the cult, based in part on the meat-cutting machines used in their daily slaughter, is not confined to Fleishgate; it occurs on many similar industrial Agri-worlds where circular ripping saws are used to grind rock, cut through steelwood roots or salvage the parts of manufacturing machines.
After the formation of the Great Rift, the Cult of the Innerwyrm spread far and wide across the Affluix Sector by using the grox-meat export network of Peregrim's World. The steroid-enhanced beasts grown by Ethod Peregrim's famous meat dynasty reached truly massive sizes, altered by the dictates of the industry's selective breeding to have vast torsos and abdomens -- large enough to contain Purestrain Genestealers sewn into their guts by Innerwyrm abattoir workers.
By sending the massive grox carcasses to a dozen different worlds in the famously paranoid Fort Adere star system, the Innerwyrm agents bypass the complex bio-scanner protocols that would otherwise have picked up on the biological tissue of the Genestealers smuggled within the meat. A new ecosystem is born on each of the infested planets, though it is not just grox meat that forms its sustenance.
- Codex: Genestealer Cults (8th Edition), pp. 32, 39
- Codex: Genestealer Cults (7th Edition), pg. 18