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Okay, let's just totally geek out here for a minute. Why aren't there any Grox, Catachan Devil, Giant Insect. or for that matter, cow and marmoset genestealers?

Grox: https://warhammer40k.fandom.com/wiki/Grox

Catachan Devil: https://warhammer40k.fandom.com/wiki/Catachan_Devil

From a practical, GW based standpoint, I get it. They long ago stopped bidding against their own profit margin by producing things that might put them in a bidding war with their own fans. But this post is not about cracking on GW, its a pure science fiction question.

Whether we're talking Genestealers or the Aliens https://en.wikipedia.org/wiki/Alien_(film) from which the idea emerged, the concept is something of a staple of sci fi, and many authors and movie makers have parroted it over the years. A highly aggressive, highly successful parasitic species that reproduces itself using the genetic material of host species. Whether they evolved natrually or were engineered by Tyranids or other intelligent monsters doesn't matter. They literally "steal genes" and force host species to become completely absorbed in procreating for them. A cool sf concept to be sure.

But, why then, don't we see unintelligent animals on genestealer infested planets undergoing the same gradual, generational conversion into genestealers that intelligent beings like humans and eldar do?

It seems this would be fairly automatic, and such creatures would become a huge part of genestealer/tyranid armies.

In fact, this concept was explored to some extent with squigs, but why don't we see huge hosts of other genestealers at the vanguard of genestealer armies?

Let's face it, only a tiny portion of the biological matter on earth is human. If a species was to successfully exploit us in this manner, wouldn't genestealer ants, marmosets and tree sloths have to be a part of it as well?

For my own part, in my scandalously ongoing heretical attempt to do 40k in 15mm, using Risk Warhammer 4,000, Alternative Armies, and Old Glory 15s as the base, I intend to exploit this, and thought I might share here.

These Giant Bugs: https://www.amazon.com/dp/B000296LPC?ref=ppx_yo2ov_dt_b_product_details&th=1 will be fairly gargantuan in 15mm scale, but I offer them just as an idea generator. In fact, they would probably work better in 28mm.

Infecting non-sapient creatures doesn't further the point of a Genestealer infection. The idea behind it is to infiltrate a society and prepare it for easy consumption by the Hive Fleets. Grox don't put up a fight against the Tyranids, Humans do.

There are. That's what the Ymarl strain came from.

Genestealer reproduction is for the purpose of attracting the attention of the hive fleets though - by creating a sufficiently powerful psychic beacon to attract the attention of a fleet.

Infecting the local farmer's cattle probably won't create a sufficiently strong psychic signal to make it worth the neighborhood hive fleet's time/effort to investigate that world over one with a large human (etc) population.

There might actually be a worthwhile point to this for the Hive Mind to pursue. Infiltrate the wildlife and plants or domesticated flora and fauna, and spread from there. Pursue all avenues to overcome organized sapient resistance. Outflank and undermine.

Absence of evidence is not evidence of absence.

This, too, might well go on. Though not necessarily via the Genestealer strain, should its highly specific niche be infiltration of sapient species. Other forms of Tyranid infiltrator organisms may exist for this purpose, including cerebral parasites. Perhaps.

 Gert wrote:
Infecting non-sapient creatures doesn't further the point of a Genestealer infection. The idea behind it is to infiltrate a society and prepare it for easy consumption by the Hive Fleets. Grox don't put up a fight against the Tyranids, Humans do.

Granted on both counts, but Grox, Catachan Devils, Giant Spiders, etc., don't fight FOR the nids either. Genestealers do.

Right, but an organised resistance by sapient beings with weapons is a far bigger road bump than some angry cows.
Genestealers subvert the local power structures either by bending them to the will of the Patriarch or by causing mass disruption when the Hive Fleets show up. If the local ruler is part of the Cult then the planet embraces the Hive Fleet as their Star Gods bringing them to their new divine beyond. If the Cult has infiltrated the parts of a society dedicated to the maintenance of infrastructure or resource production then they can cause serious problems when the Hive Fleet shows up. You can't move soldiers around if all the roads, bridges, and tunnels are destroyed.

Humans also fit into far more cogs in the wider societal machine than any wildlife does. An entire generation of Cultists could be shipped off into the Guard only to have their psychic triggers activated at a crucial moment in a far-off campaign which causes the Imperium to lose a world. Cultists might get sent off-world as part of a religious or worker group, bringing Genestealers with them and spreading the Curse to even more worlds.

It's also extremely easy to hide the Genestealer Curse in a Human population due to how varied and largely uncontrolled they are. A new religious group pops up but it worships the Emperor as a Star God which isn't super far away from the basic Imperial Cult nor is it overly radical like some other accepted sects. Those who belong to this new Cult are diligent workers and patriotic people who want to sign up for the PDF and Guard. The governor likes that their quotas are always hit and the troops sent off to the Guard seem to be well-disciplined soldiers. By the time a Hive Fleet reaches the world, the Cult has taken over as the main religious group, the PDF has a third of its ranks filled with Cultists and many of the Government's household staff are Cultists. The uprising begins and the planet is consumed before a distress call can even be made.

I cannot recommend Adrian Tchaichovsky's Day of Revelation enough when it comes to really understanding the real power of a Genestealer Cult.

 Gert wrote:


I cannot recommend Adrian Tchaichovsky's Day of Revelation enough when it comes to really understanding the real power of a Genestealer Cult.

Thanks for the book recommendation. I'll have a look.

As to the rest, I get your arguments, and they make sense, but...

What would work out better for the nids in practice, they ifiltrate an IG base, or a dairy farm.

On the one hand, each soldier they infect becomes an asset instead of a direct threat, and there could be more efficiency (arguably) in taking over an organization where everybody obeys orders. Just walk into that latrine, Corporal Schnapps, don't worry about the blood curdling screams.

However, the IG base also has commissars who are on the lookout for just this kind of thing, and protocols for containment and sounding the alarm when they do occur.

The dairy farm, OTOH? Its equally well organized, and if the farmer, the bull and the cows are all infected, who's really going to notice? The farmer's wife, kids and neighbors? Probably not. They're not on the lookout (at least not beyond the level of typical Imperial superstition) at anywhere near the level the commissariat is. And the cows would do exactly what cows do. Breed. No one would question their actions. And, to the best of my understanding, genestealers go through for generations of getting more like the host race in appearance, and then breed a new purestrain stealer.

Now, if I'm wrong about that, and a cow-stealer breeds a more stupid stealer than a human stealer does, then I'd retract that part of my argument. But even then, it seems like the more stealers that get bred overall, the stronger resistance the hive can put up when the rebellion finally takes place.

My thoughts, anyway.

The hybrids definitely would be dumber.

Also the point of a Genestealer infestation isn't to put up a resistance, but to undermine the local defenses when the Hive Fleet arrives. A Genestealer cow isn't infiltrating the local government.

 Gert wrote:
Infecting non-sapient creatures doesn't further the point of a Genestealer infection. The idea behind it is to infiltrate a society and prepare it for easy consumption by the Hive Fleets. Grox don't put up a fight against the Tyranids, Humans do.

Actually….not necessarily.

The aim of the Cult is, ultimately, to attract the Hive Fleet to a world rich in biomass to be consumed. That when infecting sentient species the Cult is driven to infiltrate the society as deeply as possible is more secondary. A further step taken to ensure the first step goes off smoothly when it’s dinner time.

Yes the ideal is for the roving Genestealers to find their way to densely populated worlds. But in theory, just infecting a Jungle World with no sentient species is still providing biomass at the end of the day. Indeed whilst not as rich as prize as say, devouring everything on a Hive World, such an infestation would likely be a real boon, particularly to the remnant of a formerly defeated Hive Fleet, as it’s Free Nosh to replenish their numbers.

@NapoleonInSpace
Infiltrating the PDF and Guard is the end stage for a Cult, not the first steps. The first steps are infecting the general masses that can go unnoticed such as those in the Underhive or who work in industries where an extra limb can be hidden under safety gear or heavy clothing. It's only those Hybrids or Cult members who can pass as baseline Humans that get to go that far.
In terms of reproduction, your example falls at the first hurdle due to one simple fact, the farm owners will notice the mutations. The psychic power held by the Patriarch and Hybrids means that those who bear the more obvious Hybrid children treat them as if they were "normal". The family will literally not notice anything though they will make sure to hide the more obvious members of their Cult from local authorities. If a Grox herd becomes infected then those very first offspring are going to get noticed and the herd gets culled unless the Human agri-workers are also infected and part of the Cult. Likewise, any produce taken from the livestock is eventually going to get noticed as being tainted with Xenos DNA and then the entire Cult gets found out and destroyed.
The point of the Cult is to go unnoticed until it's too late to stop it and that doesn't work if there has to be a massive effort to hide that entire plantations of livestock are massively tainted.

If we're talking about local wildlife? Again it just doesn't serve the purpose of what a Genestealer Cult is intended to do. Infecting the local bugs doesn't help the Patriarch subvert the power structures or gain control over the masses.

@MDG
The Genestealers attract the Hive Fleets, and the Cults destabilise the target to reduce the biomass strain on said Hive Fleet when it shows up. The latter serves the former obviously but a Patriarch needs a strong Cult to be of any use and livestock are inferior to Humans.

Yeah, but if a Genestealer finds itself stranded on a hypothetical Jungle World with no sentient life, it can still set about its dirty business, at least until an opportunity to get off-world crops up.

Provided the infection spreads far enough, the Patriarch will still start issuing the beacon.

I've got no citations to say that a Genestealer won't infect local lifeforms but it's not difficult to infer from sources that only sentient lifeforms are used to start the reproductive process.

However, a Patriarch only evolves if there is a Cult propagated. If 20 Genestealers land on a planet with no sentient life then a Cult can't be started and a Patriarch won't evolve.

 NapoleonInSpace wrote:
The dairy farm, OTOH? Its equally well organized, and if the farmer, the bull and the cows are all infected, who's really going to notice? The farmer's wife, kids and neighbors? Probably not. They're not on the lookout (at least not beyond the level of typical Imperial superstition) at anywhere near the level the commissariat is. And the cows would do exactly what cows do. Breed. No one would question their actions. And, to the best of my understanding, genestealers go through for generations of getting more like the host race in appearance, and then breed a new purestrain stealer.

Actually, meat and milk of our herds is so painstakingly purified and analyzed even today (to the point absolute sterility of milk famously started making Swiss cheese go bad and Swiss scientists had to figure out artificial dirt to make it mature properly again - and no, this is not a joke) that any sort of alien taint would be noticed immediately. I'd bet Imperium does so too seeing fresh meat and produce is something reserved for elites. Ironically, dairy farm might be the hardest to corrupt installation on any given Imperial planet. So why bother when local village population is much easier target (though funnily enough, said cult would probably need to become the cleanest part of the planetary demographic observing harsh hygiene regime so their hair, dead skin cells, etc, didn't make it to raw food as that might be picked up by above analysis too)...

 Gert wrote:
I've got no citations to say that a Genestealer won't infect local lifeforms but it's not difficult to infer from sources that only sentient lifeforms are used to start the reproductive process.

However, a Patriarch only evolves if there is a Cult propagated. If 20 Genestealers land on a planet with no sentient life then a Cult can't be started and a Patriarch won't evolve.

It’s down to their purpose.

Genestealers are sent out ahead of the Hive Fleets to identify and infiltrate prey Worlds, yes?

It makes zero sense in terms of genetic imperative or whatever you wish to call it, for them to arrive on a biomass rich world and then just do nothing, because there’s nothing sentient to infect. Indeed the Hive Fleets don’t prey on such worlds by preference - they just tend to be the invasions were hear about.

Yes the infection needs to get to a certain size to attract a Hive Fleet - but that infection by no means would need to be a Cult as we understand them.

A thriving jungle world probably has more biomass available than an ecologically devastated hive world.

 Haighus wrote:
A thriving jungle world probably has more biomass available than an ecologically devastated hive world.

In terms of variety? Almost definitely. But given a Hive World has multiple Hives, and each Hive houses billions of humans? I think the Hive world would have more overall.

Upside though is variety is the spice of life, and the Hive Mind might find an utterly unique lifeform, and derive new adaptations and that from it.

I doubt it, the mass of things like trees and microbiota is huge.

For reference, our heavily deforested planet still has >3 trillion trees. Only the largest hive worlds will have populations approaching or exceeding that, and I'd hazard a typical tree weighs more than a typical person. In addition, a world covered by jungle is going to have much larger numbers of trees (or local tree equivalents).

Again though, as to what the OP asked, there is no need to form a bond with local wildlife when there are Humans/other sentient lifeforms on a given world. A high biomass world with no sentient life is outwith the question asked because its a completely different set of parameters.

 Gert wrote:
Again though, as to what the OP asked, there is no need to form a bond with local wildlife when there are Humans/other sentient lifeforms on a given world. A high biomass world with no sentient life is outwith the question asked because its a completely different set of parameters.

Well, it is still interesting to consider what genestealers do when encountering such worlds. I strongly suspect they can infect other large non-sentient lifeforms, even if they normally don't.

I think there is an edge case of worlds with high biomass, and present-but-small populations of sentient life. In such a scenario, it may be beneficial for the genestealers to establish themselves deep in the jungle to provide a safe haven before infiltrating the sentient populations, especially if the genestealer(s) initially entered the world far from any sentient populations (for example in a shuttle crash). Catachan could be a good example of a world like this.

 Gert wrote:
Again though, as to what the OP asked, there is no need to form a bond with local wildlife when there are Humans/other sentient lifeforms on a given world. A high biomass world with no sentient life is outwith the question asked because it’s a completely different set of parameters.

That’s fair, and we’ll learn me to read an OP properly.

 Haighus wrote:
I doubt it, the mass of things like trees and microbiota is huge.

For reference, our heavily deforested planet still has >3 trillion trees. Only the largest hive worlds will have populations approaching or exceeding that, and I'd hazard a typical tree weighs more than a typical person. In addition, a world covered by jungle is going to have much larger numbers of trees (or local tree equivalents).

Keep in mind that organic creatures aren’t made of purely organic matter. Tyranids harvest everything on a world, including metals, minerals, and dirt, only stopping when they hit the bedrock.

So while a large-scale jungle planet might have more purely BIO matter, a hive world is going to be far more nutrient rich on an over-all scale.

 morganfreeman wrote:

 Haighus wrote:
I doubt it, the mass of things like trees and microbiota is huge.

For reference, our heavily deforested planet still has >3 trillion trees. Only the largest hive worlds will have populations approaching or exceeding that, and I'd hazard a typical tree weighs more than a typical person. In addition, a world covered by jungle is going to have much larger numbers of trees (or local tree equivalents).

Keep in mind that organic creatures aren’t made of purely organic matter. Tyranids harvest everything on a world, including metals, minerals, and dirt, only stopping when they hit the bedrock.

So while a large-scale jungle planet might have more purely BIO matter, a hive world is going to be far more nutrient rich on an over-all scale.

Not sure how much of the structure of a hive is digestible to tyranids. Usually depictions of digested worlds show the shattered skeletons of human structures left behind, still visibly recognisable.

Hive worlds strike me as good targets for the strategic benefits of taking out a centre of resistance over the nutritional value of such toxic, stripped worlds.

 Haighus wrote:

Not sure how much of the structure of a hive is digestible to tyranids.

Probaly most if not all of it according to Devastation of Baal. Moreover they prefer refined metals over natural deposits.

Devastation of Baal wrote:Lights from the Splendid Pinion’s subsidiary craft played over the broken station orbiting Sciothopa. Glaring circles of bright light turned bent girders into shining filigree. Large parts of the station structure
were missing, and the rest was close to disintegration. Erwin reckoned it would only be a few weeks before the remains were dragged from the sky by Sciothopa Prime and smashed to atoms on the surface.

‘They take even the metal,’ said Erwin.
[...]
‘They take minerals of every kind, my lord,’ said the servile. ‘I have compared spectrographic analysis of this world with records of how it was. It shows massive depletion of all main range elements. The devourer remakes the worlds it consumes. Although I notice a small inconsistency with the oldest records of tyrannic-stripped worlds.’
[...]
‘The older worlds show a larger loss of mass. The tyranids spent longer on each, digesting parts of the planetary crust. They do not remain so long as they once did. Once the biological components of the world have been devoured, they target only sources of refined metals, such as the Mechanicus station here, in preference to the source minerals.’

‘Then they are running scared, feeding, moving on before they can be interrupted,’ said Erwin. ‘Commander Dante has them afraid.’

‘Or, my lord, they are presented with a surfeit of food. They have nothing to fear. They have too much choice. The Imperium is a banquet to them. They have become fussy eaters.’

Also matches the revelation from the Cawl novel, that whilst they do consume most stuff, enough remains that, given time (lots, and lots, and lots, and lots, and lots) of time, a world can regenerate its biosphere and biome.

The Imperium of course can speed this along somewhat via terraforming.

It is extremely unlikely for a world to naturally get the oceans and atmosphere back.

Cawl can do it by pulling water from the mantle and artificially creating a new atmosphere, but that is a blatant artificial terraforming.

 Tyran wrote:

 Haighus wrote:

Not sure how much of the structure of a hive is digestible to tyranids.

Probaly most if not all of it according to Devastation of Baal. Moreover they prefer refined metals over natural deposits.

Spoiler:

Devastation of Baal wrote:Lights from the Splendid Pinion’s subsidiary craft played over the broken station orbiting Sciothopa. Glaring circles of bright light turned bent girders into shining filigree. Large parts of the station structure
were missing, and the rest was close to disintegration. Erwin reckoned it would only be a few weeks before the remains were dragged from the sky by Sciothopa Prime and smashed to atoms on the surface.

‘They take even the metal,’ said Erwin.
[...]
‘They take minerals of every kind, my lord,’ said the servile. ‘I have compared spectrographic analysis of this world with records of how it was. It shows massive depletion of all main range elements. The devourer remakes the worlds it consumes. Although I notice a small inconsistency with the oldest records of tyrannic-stripped worlds.’
[...]
‘The older worlds show a larger loss of mass. The tyranids spent longer on each, digesting parts of the planetary crust. They do not remain so long as they once did. Once the biological components of the world have been devoured, they target only sources of refined metals, such as the Mechanicus station here, in preference to the source minerals.’

‘Then they are running scared, feeding, moving on before they can be interrupted,’ said Erwin. ‘Commander Dante has them afraid.’

‘Or, my lord, they are presented with a surfeit of food. They have nothing to fear. They have too much choice. The Imperium is a banquet to them. They have become fussy eaters.’

I stand corrected.

I do feel like I have read somewhere that adamantium is difficult for Tyranids to digest, which may be a way of squaring this circle- most of the Imperial structures are eaten, but the adamantium skeleton is largely left behind.

Maybe but the 4th edition codex specifically calls out that Carnifex tusks as being laced with adamantium so they can definitely use it.

Difficult isn’t the same as impossible.

Another argument is the effort to utility. If you only use Adamantium sparingly, you don’t need to consume a huge amount of it?

 Irbis wrote:

 NapoleonInSpace wrote:
The dairy farm, OTOH? Its equally well organized, and if the farmer, the bull and the cows are all infected, who's really going to notice? The farmer's wife, kids and neighbors? Probably not. They're not on the lookout (at least not beyond the level of typical Imperial superstition) at anywhere near the level the commissariat is. And the cows would do exactly what cows do. Breed. No one would question their actions. And, to the best of my understanding, genestealers go through for generations of getting more like the host race in appearance, and then breed a new purestrain stealer.

Actually, meat and milk of our herds is so painstakingly purified and analyzed even today (to the point absolute sterility of milk famously started making Swiss cheese go bad and Swiss scientists had to figure out artificial dirt to make it mature properly again - and no, this is not a joke) that any sort of alien taint would be noticed immediately. I'd bet Imperium does so too seeing fresh meat and produce is something reserved for elites. Ironically, dairy farm might be the hardest to corrupt installation on any given Imperial planet. So why bother when local village population is much easier target (though funnily enough, said cult would probably need to become the cleanest part of the planetary demographic observing harsh hygiene regime so their hair, dead skin cells, etc, didn't make it to raw food as that might be picked up by above analysis too)...

Not only that - which is an excellent point - but there are other factors in commercial livestock farming that would present dead-ends for genestealers. Parent animals and offspring are routinely separated. Male animals are usually either killed or castrated before they reach sexual maturity. Conventional insemination is rare, artificial insemination more common. So your whole cycle of hybridization would have real problems to get of the ground, as most of your male first-generation hybrids would be slaughtered before they could reproduce, and even if they could they would get no access to female animals to do it. That all depends on the set-up obviously, if you got free-running herds like in the old west it would work out differently, although even then the breeding bulls tended to be specially selected. Cowboy inquisitors coming up against genestealer-related cattle-mutilitians would be one hell of a setting for a story though

Genestealers are interested in intelligent life, because intelligent life builds spaceships. The goal of a genestealer infestation is twofold.

1) Weaken the defenses of an existing world by infecting the population and create a psychic beacon that lures the hivefleet there.

2) Sneak genestealers aboard ships to continue spreading across the galaxy.

Both of these goals require intelligent hosts.



I'm sure a Genestealers can infect lower lifeforms, but it isn't the goal and would probably be a deadend for the genestealer that did it.

I could see a Genestealer aboard a ship that crashlands on a uninhabited planet, perhaps having infected the small number of crew(or maybe none of them survive the crash) then struggle as it explores the planet devoid of anything intelligent to infect. So it infects lower lifeforms, but this just results in an intelligent but limited animal brood that is stuck on a planet with little hope of drawing in a hive fleet and none of spreading further.

Maybe you have a genestealer cult made up of infected Ape/monkeylike creatures in a primitive mockery of a real genestealer cult. The cult devolving over the generations into aggressive fauna. Perhaps this was the origin of some of the nastier things in the galaxy like the Catachan Devil. Genestealers forced to infect animals and being neutralized by their lack of intelligence.