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 Tyran wrote:
The galaxy is simply way too big for a concentrated force like the Great Crusade to fight Hive Fleets even if we assume the GC wins each and every fight.

400-200 billions of stars, billions of inhabitated worlds, a lot of potential food and space for a mere 2 million Space Marines to patrol.

This is the big question mark about the Tyranids- why do they go for inhabited worlds at all? Assuming that, for whatever reason, they tend to avoid harvesting matter from lifeless worlds like gas giants makes them much more fightable. If they can harvest none-biological matter reliably on mass, then obviously the hive fleets can become insanely powerful without ever fighting an enemy before completely rolling over the few remaining systems with lifeforms present.

 Haighus wrote:

 Tyran wrote:
The galaxy is simply way too big for a concentrated force like the Great Crusade to fight Hive Fleets even if we assume the GC wins each and every fight.

400-200 billions of stars, billions of inhabitated worlds, a lot of potential food and space for a mere 2 million Space Marines to patrol.

This is the big question mark about the Tyranids- why do they go for inhabited worlds at all? Assuming that, for whatever reason, they tend to avoid harvesting matter from lifeless worlds like gas giants makes them much more fightable. If they can harvest none-biological matter reliably on mass, then obviously the hive fleets can become insanely powerful without ever fighting an enemy before completely rolling over the few remaining systems with lifeforms present.

I've thought about this and my theory is that Tyranids have several stages of feeding

Right now they "could" feed in gas giants and such, we actually have lore from the 3rd edition Codex that supports them doing this and up to consuming suns as well.

However I think currently the Tyranids are in a pacification mode. They attack population centres and key military spots and buildup points because those are a threat. Their intention right now isn't to feed, but to pacify the galaxy. So they leave all the big juicy easy food sources because those don't really do anything for the other races right now. Instead they go for worlds that are of benefit to the Imperium, Orks and other races. Things that threaten the actions of the Tyranids.

I would say that after they pacify the galaxy we would see them start to feed properly and go into a grazing mode. There might even be insanely vast leviathan ships hiding out in the black that travel the distance between Galaxies. The "bulk" of the swarm manifest that come in to feed in peace and safety before heading back out into the vast voids between Galaxies.



Tyranids might be the Great Devourer, but their actions are far from simply sating a mindless hunger. Their hunger is focused, targeted and specific.

 Overread wrote:

 Haighus wrote:

 Tyran wrote:
The galaxy is simply way too big for a concentrated force like the Great Crusade to fight Hive Fleets even if we assume the GC wins each and every fight.

400-200 billions of stars, billions of inhabitated worlds, a lot of potential food and space for a mere 2 million Space Marines to patrol.

This is the big question mark about the Tyranids- why do they go for inhabited worlds at all? Assuming that, for whatever reason, they tend to avoid harvesting matter from lifeless worlds like gas giants makes them much more fightable. If they can harvest none-biological matter reliably on mass, then obviously the hive fleets can become insanely powerful without ever fighting an enemy before completely rolling over the few remaining systems with lifeforms present.

I've thought about this and my theory is that Tyranids have several stages of feeding

Right now they "could" feed in gas giants and such, we actually have lore from the 3rd edition Codex that supports them doing this and up to consuming suns as well.

However I think currently the Tyranids are in a pacification mode. They attack population centres and key military spots and buildup points because those are a threat. Their intention right now isn't to feed, but to pacify the galaxy. So they leave all the big juicy easy food sources because those don't really do anything for the other races right now. Instead they go for worlds that are of benefit to the Imperium, Orks and other races. Things that threaten the actions of the Tyranids.

I would say that after they pacify the galaxy we would see them start to feed properly and go into a grazing mode. There might even be insanely vast leviathan ships hiding out in the black that travel the distance between Galaxies. The "bulk" of the swarm manifest that come in to feed in peace and safety before heading back out into the vast voids between Galaxies.



Tyranids might be the Great Devourer, but their actions are far from simply sating a mindless hunger. Their hunger is focused, targeted and specific.

But the other forces (with the possible exceptions of Eldar and Necrons) struggle to identify the locations of hive fleets beyond the vague area of the Shadow in the Warp. It is one of the chief challenges of countering Tyranids- your psykers can work out vaguely where they are from the Shadow, but which systems are actually being attacked within that shadow is frequently unknown. That is why sending reinforcements is so tough, they might arrive at the wrong world, let alone too late to help.

So fleets harvesting dead systems should be considerably safer, on the whole, and able to harvest much greater quantities of raw materials than those jumping from biosphere to biosphere. Earth's biosphere has an estimated mass of up to 4 trillion tons. The Earth has a mass of about 6x10^21 tons. Jupiter has a mass of nearly 320 Earths, and that is the entire Earth not just the biosphere. One Jupiter is something like 475 billion biospheres from Earth-equivalent planets. Now, Jupiter is almost entirely hydrogen and helium (with current knowledge) but hydrogen especially is very useful and there are still enormous quantities of other substances like ammonia and organic compounds. Plus, harvesting smaller rocky planets and asteroids etc. will add a lot of the other elements to the pool.

It seems, to me, that there is some reason why this only happens rarely in the 40k timeline. It may be as simple as the currently-encountered fleets being a probing, insignificant vanguard that the Hive mind barely even acknowledges and is already serving its purpose in the current incarnation. Scout mode not pacification mode. More efficient fleets might not yet have arrived. The other rationale that stands out to me is one of energy efficiency. Absorbing an entire system may be enormously energy intensive and slow, whereas skimming off a biosphere is quick and efficient. So fleets that have expended a lot of energy crossing the void prefer a quick and easy snack to a slow feed that might put them into energy debt in the short term.

Tyranids do need biomass though.

Of course, origin of life research is ongoing in the real world, and I don’t think we’ve quite figured out how the first organisms came to be - though having followed Professor Dave’s takedown of James Tour I’m aware there are promising leads in that area.

So I guess there’s an open question on whether by scoffing gas giants and minerals the Hive Mind could create very basic life from scratch. Nothing fancy like, but enough to create biomass. If it could, its options are widened when more substantial sources can’t be taken, and again introduces a further source of patience.

Whether that could create sufficient stock to recover a splinter fleet to a Hive Fleet? Very much open to argument. So it’s not a simple fix for a Hive Fleet losing a war of attrition, left unable to replace losses or produce new adaptations in any significant number.

 Mad Doc Grotsnik wrote:
Tyranids do need biomass though.

Of course, origin of life research is ongoing in the real world, and I don’t think we’ve quite figured out how the first organisms came to be - though having followed Professor Dave’s takedown of James Tour I’m aware there are promising leads in that area.

So I guess there’s an open question on whether by scoffing gas giants and minerals the Hive Mind could create very basic life from scratch. Nothing fancy like, but enough to create biomass. If it could, its options are widened when more substantial sources can’t be taken, and again introduces a further source of patience.

Whether that could create sufficient stock to recover a splinter fleet to a Hive Fleet? Very much open to argument. So it’s not a simple fix for a Hive Fleet losing a war of attrition, left unable to replace losses or produce new adaptations in any significant number.

Tyranids are not creating life from scratch though, they only need raw materials to feed into their existing organisms.

Life on Earth already has mechanisms for fixing more-or-less all of the common elements into biomass from non-biological forms. Tyranids canonically absorb capabilities from the genetic material of species they eat. It would be trivially easy for them to have methods to absorb nutrients that are not currently biomass and turn them into biomass- every world they consume will feature methods for doing so.

That’s true, I guess.

Photosynthesis could be one route, even just using solar radiation?

 Mad Doc Grotsnik wrote:
That’s true, I guess.

Photosynthesis could be one route, even just using solar radiation?

Photosynthesis is definitely an example for carbon, hydrogen, and oxygen fixing. How that would be powered is a good question, and the energy needed might explain why hive fleets don't like doing it from scratch when they can just eat biomass. Photosynthesis also stores energy as chemical energy though, so less energy intensive alternatives almost certainly exist.

I guess it’s the difference between us smelly hoomans

1. Sewing, growing and eating the seed.
2. Buying stuff in at the beginning of the week and cooking from scratch
3. Sod it, let’s go to McDonalds.

Most of us, left with no alternative, probably could do 1. But we’re also all prone to 3 when we just can’t be arsed to 2.

Whilst of course a massively oversimplified and very silly example, the Hive Mind may well have a similar thought process. When the buffet is open, gorge yourself. Save the subsistence tactics for when that’s the only one open to you.

Or, potentially, do that between densely populated systems so you can get your vitamins in peace?

 Mad Doc Grotsnik wrote:
I guess it’s the difference between us smelly hoomans

1. Sewing, growing and eating the seed.
2. Buying stuff in at the beginning of the week and cooking from scratch
3. Sod it, let’s go to McDonalds.

Most of us, left with no alternative, probably could do 1. But we’re also all prone to 3 when we just can’t be arsed to 2.

Whilst of course a massively oversimplified and very silly example, the Hive Mind may well have a similar thought process. When the buffet is open, gorge yourself. Save the subsistence tactics for when that’s the only one open to you.

Or, potentially, do that between densely populated systems so you can get your vitamins in peace?

The bit that is different, and where this discussion originates, is that (to follow your analogy) the McDonalds has barred you, so you need to get past the security guard(s) first who might be able to call the police in for support before you get chance to eat Suddenly 1 and 2 look more appealing...

Even then, not really.

The galaxy has billions of inhabited worlds, of which humanity only controls a million, of which only a handful have strong enough defences to actually contest a hive fleet.

The Hive Mind can basically randomly throw hive fleets at inhabited worlds and only one in a million will be strongly defended.

 Haighus wrote:


So fleets harvesting dead systems should be considerably safer, on the whole, and able to harvest much greater quantities of raw materials than those jumping from biosphere to biosphere. Earth's biosphere has an estimated mass of up to 4 trillion tons. The Earth has a mass of about 6x10^21 tons. Jupiter has a mass of nearly 320 Earths, and that is the entire Earth not just the biosphere. One Jupiter is something like 475 billion biospheres from Earth-equivalent planets. Now, Jupiter is almost entirely hydrogen and helium (with current knowledge) but hydrogen especially is very useful and there are still enormous quantities of other substances like ammonia and organic compounds. Plus, harvesting smaller rocky planets and asteroids etc. will add a lot of the other elements to the pool.

It seems, to me, that there is some reason why this only happens rarely in the 40k timeline. It may be as simple as the currently-encountered fleets being a probing, insignificant vanguard that the Hive mind barely even acknowledges and is already serving its purpose in the current incarnation. Scout mode not pacification mode. More efficient fleets might not yet have arrived. The other rationale that stands out to me is one of energy efficiency. Absorbing an entire system may be enormously energy intensive and slow, whereas skimming off a biosphere is quick and efficient. So fleets that have expended a lot of energy crossing the void prefer a quick and easy snack to a slow feed that might put them into energy debt in the short term.

It could be scout mode, but I'd argue that targeting worlds like the Homeworld of Ultramarines and Blood Angles suggests that its more pacification than scouting. You don't "scout" those worlds you target them for specific removal.

Now it could be what we have is a vanguard instead of the main army, but I'd argue its very much pacification.


Meanwhile yes they could harvest from gas giants and the like and not be bothered; but it might well be part of their genetic/core construct that Tyranids just don't do that until the Galaxy is safe for them. When they can travel between the void it doesn't matter if the war takes another 1000 years; they can wait that long as that timespan is nothing to the time between Galaxies.


It might also be an escalation element in that previous experience is that the more pressure they apply the more the Galaxy they are invading resists. Ergo if they start feeding on many worlds and becoming too big of a threat you might see more factions unite. Orks, Imperials, Eldar, Tau and Necrons are all 100% capable of putting aside differences and uniting against a common foe like a vast Tyranid invasion. In fact they've done it in the lore several times in small parts here and there. Furthermore some weapons, like sun and planet killers; are used very sparingly because the feeling is that the Tyranids are "a threat" but not quite enough to blow up most of your "back lawn" to defeat. Instead if the Swarm suddenly became too big too fast; those superweapons might get far more justification to be used.

Ergo the Tyranid approach could be Pacification with the least amount of force possible so that they can do the most damage without their foes committing too much or uniting; until the Tyranids have a vast upper-hand and those measures are too little too late.

Harvesting from gas giants and non-inhabited worlds is also a slower, more time intensive process.

Attacking inhabited and developed worlds means they get to eat the highly refined and processed metals and other minerals found in artificial infrastructure.

In Devastation of Baal it is even stated that Tyranids will often ignore natural mineral resources in favor of artificially refined ones. Humanity basically already did the heavy pre-digestion process of planetary crust for them.

 Tyran wrote:
Harvesting from gas giants and non-inhabited worlds is also a slower, more time intensive process.

Attacking inhabited and developed worlds means they get to eat the highly refined and processed metals and other minerals found in artificial infrastructure.

In Devastation of Baal it is even stated that Tyranids will often ignore natural mineral resources in favor of artificially refined ones. Humanity basically already did the heavy pre-digestion process of planetary crust for them.

That and the artificial stores benefit humanity (or other races). So again its Tyranids denying their foe resources whilst bolstering their own. It allows Tyranids to rapidly move planet to planet. Each time they win they grow stronger and their enemy loses a world. Even if the Hive Fleet eventually gets defeated, their foes have suffered far more and those worlds will take generations to rebuild and cost a massive amount of resources. Meanwhile those worlds are still food sources for the greater swarm in time; so the Tyranids have also not wasted everything fighting over it.

I do like the pacification theory. After all, a Hive Fleet is highly vulnerable when feeding, so looking to ensure nobody is in a position to attack you.

But I do imagine there’ll be elements of a given tendril, let alone overall fleet, off to scoff softer targets at the same time, just in case the main invasion is repulsed


Automatically Appended Next Post:
But, back to the main question 🤣🤣

I think the biggest advantage the Great Crusade would have is when it wins an engagement, it’s more likely to be in a position to properly follow that victory up, inflicting greater and possibly lasting damage. And due to numbers, and the stockpiles of really, really filthy weapons held in Crusade Fleets? I think said victories may be more common. Certainly the supply lines feel more solid in that era, as do lines of communication.