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I'm playing around with an Imperial Guard vs Tyranid story and I want to get your opinions on how selective Tyranids are when it comes to planets.

In this story, the Tyranids invade a planet (obviously). In the same system, their is a moon that is used for extreme environment training. The moon, once habitable, has at some point in history been rendered inhospitable from thermonuclear war. The moon is now a white pearl in sky, covered with a thin layer of ash and dust broken up by the burned ruins of old cities. Not exactly a bread basket.

So, a group of greenhorns are being drilled on the dead moon when the splinter fleet passes through the system. Do the Tyranids descend on the dead moon or do they turn their nose up at them and move on to fatter prey?

Further more:
. How do Tyranids decide their targets?
. What worlds will they avoid and which will they merely save for last?

I think Tyranids devour every world they can. They'll still go for the moon because of the IG and minerals there.

Tyranids thrive on biomass. Since the moon offers very little they would likely only descend if there was a valuable mineral the hive requires to strengthen itself. Remember that the hive expends resources every time it makes planet fall so it calculates this when making the choice to devour a planet or bypass.

If Tyranids reach a system, the strip all of it for biomatter before moving on to the next one.

I think I need to clarify. The moon is not the only occupied place in the system, there is also a planet with hive cities and life on it.

My question is more about prioritization. would a splinter fleet attack every planet at once, or would they target the planets individually?

The tyranids would drop some creatures onto the moon to scout it and kill the guardsmen. They might not deploy spawning pools or large harvesting creatures, but they would want to get at the guardsmen.

In the ultramarines novel they definitely scoured the less useful moons before moving on to the planet. I distinctly remember a scene where the inhabitants barricade their townstead to no avail. They will land on the moons and the asteroids and everywhere in the system, although the might not eat it before moving on.

Depends on the Hive Fleet, specifically. If it is relatively new, and has never encountered humans before, it might think that it can just attack all of the planets at once... which, if faced with stiff resistance from Space Marines/IG/whatever, will be detrimental to the Hive. It can produce only so many bugs without replenishing its stores of biomass and, unless and until the Fleet can establish capillary towers on the planets it is invading, it is not possible to do that.

This is why the other, older Hive Fleets have learned to attack tactically, taking out the worlds that support the Fortress Worlds, starving the defenders of food and ammunition, gathering up large stores of biomass, before moving against the more heavily-defended planets.

Don't all Fleets learn at the same time since they're ruled by the same Mind?

pm713 wrote:
Don't all Fleets learn at the same time since they're ruled by the same Mind?

Nope. They are all under the same general idea, but each fleet is different.


Sometimes, who seperate fleets will land on a barren world and fight until one wins. They then eat the losers and become stronger that way.



When the Tyranids attack a world, it can be several hundred kilometres smaller in diameter due to everything of value having been sucked from it.

I mean really they will do what the story needs them to do, strictly speaking. There's nothing to stop you coming up with some story maguffin that masks the presence of any biomass on the moon from the hive fleet if that's what you want to do.

Perhaps the radiation from all the nuclear wars has soured it's taste to the hive mind. Or maybe a particularly nasty psyker was killed on the moon that similarity soured the milk so to speak.

 Mr Nobody wrote:
I'm playing around with an Imperial Guard vs Tyranid story and I want to get your opinions on how selective Tyranids are when it comes to planets.

In this story, the Tyranids invade a planet (obviously). In the same system, their is a moon that is used for extreme environment training. The moon, once habitable, has at some point in history been rendered inhospitable from thermonuclear war. The moon is now a white pearl in sky, covered with a thin layer of ash and dust broken up by the burned ruins of old cities. Not exactly a bread basket.

So, a group of greenhorns are being drilled on the dead moon when the splinter fleet passes through the system. Do the Tyranids descend on the dead moon or do they turn their nose up at them and move on to fatter prey?

Further more:
. How do Tyranids decide their targets?
. What worlds will they avoid and which will they merely save for last?

The Hive Mind thinks strategically, and learns from previous invasions and planetary absorption efforts. The alleged early Tyranid incursions in the centuries since the Pharos incident, were probably just scouting parties. Before Behemoth went balls-to-the-wall (to name an example), it carefully gathered biomass from planets with no intelligent life in preparation for invasion. It's initial strikes were probably intended to be a complete surprise.


The Kraken and Leviathan waged brilliant strategic campaigns against the Imperium, and learned more about other races that could (or could not) be OM NOMmed. And the constant threat of splinter fleets keeps up the pressure on the 'Nids' soon-to-be "All You Can Eat Buffet".


The Hive Mind isn't purely instinct driven to feed. It will pick and choose based on it's strategy or needs. Kraken was notorious for bypassing worlds (isolating them for later) and attacking "lesser" planets unexpectantly, forcing the Imperium to abandon entire groups of worlds to better defend strategically important planets, like Forge Worlds and Hive Worlds. This is the mark of strategic planning and thinking.


The Tyranids tend to bypass Necron and pure Daemon Worlds. However, they will attack Chaos held worlds to gather needed biomass. They will also engage daemonic and Necron forces if the Hive Mind judges them to be a threat.


So, your greenhorns should be safe if the 'Nids didn't pick up on their biomass or activity. The Hive Mind has bigger fish to fry than scouring every celestial body for the least amount of biomass to NOM.

If the Imperial presence on the Dead world is minimal that I won't give off a noticeable heat signature (or perhaps the Thermonuclear radiation in the atmosphere interferes with how 'Nids detect prey?) then I'd say it's perfectly acceptable for a Hive fleet to by-pass the training world.

I assume, story wise, you want an excuse for your protagonists to evade the initial brunt of the Hive Fleet invasion while still being in a good position to strike back at the Tyranids. You've picked a great way to do it, I think it's perfectly reasonable for a squad out in extreme training conditions to look up in the sky to see their homeworld being invaded by Tyranids. I'd like to read that story.

pm713 wrote:
Don't all Fleets learn at the same time since they're ruled by the same Mind?

Yes, but only the actual Fleet has the genetic codes. The Hive Mind is vastly intelligent, but in the same way a hunting lion is intelligent. Its not a genetic scientist and it can't make the genes from scratch, so it needs the other fleets to absorb the same biomass t get it everywhere. Sometimes it'll make 2 Hive Fleets fight to see which one is superior, the other becoming fuel to power up the winner and increase its power.

Isnt this what Genestealers, hybrids and Broodlords are designed for; to work out where the good targets are and how much force to assign? Its been a while since I read up on this so I could be way off.

 Deadshot wrote:

pm713 wrote:
Don't all Fleets learn at the same time since they're ruled by the same Mind?

Yes, but only the actual Fleet has the genetic codes. The Hive Mind is vastly intelligent, but in the same way a hunting lion is intelligent. Its not a genetic scientist and it can't make the genes from scratch, so it needs the other fleets to absorb the same biomass t get it everywhere. Sometimes it'll make 2 Hive Fleets fight to see which one is superior, the other becoming fuel to power up the winner and increase its power.

What I meant was they have the same knowledge. Hive Fleet A will fight Xenos X. Hive Fleet A is wiped out but because there's a Hive Mind all other Hive Fleets will know what tactics are effective against Xenos X.

pm713 wrote:

 Deadshot wrote:

pm713 wrote:
Don't all Fleets learn at the same time since they're ruled by the same Mind?

Yes, but only the actual Fleet has the genetic codes. The Hive Mind is vastly intelligent, but in the same way a hunting lion is intelligent. Its not a genetic scientist and it can't make the genes from scratch, so it needs the other fleets to absorb the same biomass t get it everywhere. Sometimes it'll make 2 Hive Fleets fight to see which one is superior, the other becoming fuel to power up the winner and increase its power.

What I meant was they have the same knowledge. Hive Fleet A will fight Xenos X. Hive Fleet A is wiped out but because there's a Hive Mind all other Hive Fleets will know what tactics are effective against Xenos X.

Tactics, yes, but being able to form those tactics is another matter. For example, what if the best tactics to use is simply deploy hundreds of Zoanthropes and use their psychic lances, because the enemy is entirely heavy-mechanised columns that are impervious to everything else, and biotitans are too costly? But Hive Fleet X, which has the special eldar gene needed for making Zoanthropes, is wiped out, and Hive Fleet Y never comes across Eldar or remenant of X, and so cannot make Zoanthropes as they lack the secret ingrediant gene, and so cannot beat Xenos X because Xenos X has Warlord Titans and stomp Heirophants like ants.

 Imateria wrote:
If Tyranids reach a system, the strip all of it for biomatter before moving on to the next one.

Only if its economically viable. if there are just 100 grunts on a rock, its not economically viable to drop the who Nid military/digestion complex on.

Now there is another alternative that may also be interesting for your story.
No reason they might not drop a a genestealer on the surface. After all, its a method they use for hulks etc., and its an excellent way to call further munchies to the planet...

 JustALittleOrkish wrote:
Isnt this what Genestealers, hybrids and Broodlords are designed for; to work out where the good targets are and how much force to assign? Its been a while since I read up on this so I could be way off.

Kinda. Genestealer Cults more or less act as a way to destabilize the societal system of a planet in preparation for the Hive Fleet and act as a psychic lighthouse for the Hive Fleet to follow. They don't really relay any strategic information. They act fairly autonomously up until the cult grows big enough to act as a giant dinner bell for the Hive Fleet. At that point they band together and attack the planet's inhabitants, creating a distraction from the looming threat of the full Tyranid forces that are coming.

Lictors are more the unit that Tyranids use as intelligence-gathering scouts. Lictors will eat the brains of local inhabitants, thus making their knowledge, memories, and potential weaknesses an exploitable advantage for when the Hive Fleet arrives. It also allows them to prepare necessary resources based on the information the Lictors gather.

Basically, Genestealers and their Cults are like "Here, eat this!" and Lictors are like "Hey, this is how we should go about eating this!"

 Frazzled wrote:

 Imateria wrote:
If Tyranids reach a system, the strip all of it for biomatter before moving on to the next one.

Only if its economically viable. if there are just 100 grunts on a rock, its not economically viable to drop the who Nid military/digestion complex on.

Now there is another alternative that may also be interesting for your story.
No reason they might not drop a a genestealer on the surface. After all, its a method they use for hulks etc., and its an excellent way to call further munchies to the planet...

I like this idea. It would certainly be one hell of a good motivator to get them moving.