Why don't Tyranids just devour planets whole?

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**Warboss Imbad Ironskull**

Cobourn wrote:Stages of Planetary Consumption:

Generally, contact with the Tyranids occurs when a Hive Fleet invades a star system for the purpose of harvesting its inhabited worlds' biomass. A Hive Fleet contains an enormous number of Tyranids, and they are brought to bear against resistance in the most efficient manner possible.

Below is a general outline of a typical Tyranid planetary assault (in particular, this data is collected from the Tyranid invasion of Dalki-Prime):

■Day 01: Mycetic spores are dropped, mostly containing Lictors and Genestealers. As soon as they hit the ground, the reproduction of Tyranid creatures likely begins immediately.

■Day 09: By now, the Tyranid infestation will have expanded to around 250 km around the drop point, and will likely present a significant threat to planetary defense force troopers and the resident Imperial Guard.

■Day 13: Tyranids have expanded to 700 km from the drop point; some may begin infesting local water sources.

■Day 37: Tyranids completely control the area within 2,000 km radius of the drop point and basolithic infestation has begun to reach a 5,000 km radius from the drop point of the first mycetic spores.

■Day 48: Tyranid population growth becomes exponential, with population doubling approximately every 3 days.

■Day 50: The main Hive Fleet arrives, with the number of Tyranid craft in the swarm generally numbering around 1.5 billion. All psychic contact with the planet through the Warp is cut off by the Warp shadow of the Hive Mind. Any attempts to escape are quickly stopped by the Hive Fleet. Any remaining surface life is eliminated by Gaunts.

■Day 51: Primary consumption of planetary biomass begins (any sentient resistance has generally been eliminated by now). Brood ships land, releasing Ripper swarms, which consume all organic material (even the other Tyranids) and deposit it at the reclamation pools. Capillary towers (and the Brood ships) send the material into orbit for use by the Hive Fleet.

■Day 80: Ripper swarms board the Brood ships and return to the Hive Fleet. The hive ships descend into the upper atmosphere and begin collecting it. Reduction in atmospheric pressure causes oceans to boil away, which are also collected so that their free water can beused by the fleet. The loss of ocean mass causes plate tectonic shifts, dramatically increasing volcanic activity across the victimized world. Upon completion, the Hive Fleet reenters the Warp, in search of fresh prey.

■Day 100: The Imperial Navy arrives in response to the planet's original Astropathic distress call, only to find a destroyed, lifeless, uninhabitable planet.

Some of this is no longer canon (for example the Tyranids no longer use the warp to travel).

I think that the Tyranids don't eat the whole planet because the gases that Mycetic Spores release (they aren't all used to transport beasties) as well as those released by the tyranid bio spires aren't capable of breaking down billions upon billions of tons of rock into the bio mass gruel that is consumed by the Tyranids.

And while DNA is important to the Tyranids as it allows them to adapt keep in mind that they are all living creatures in one way or another and so much of the harvested biomass goes to providing the energy for all those life forms either by creating them or allowing them to live.

Minerals (magma and lava are just minerals in liquid form) hold very little nutrients and so the energy spent breaking them down woulden't be worth the energy consumed from them. That's why very few if any creatures on Earth eat rocks for purpose of protein, now yes some minerals are important and are ingested through the food we eat but that food isn't rock. It's the same thing with the Tyranids, they're just a mass of living creatures seeking to further their existance on a planetary scale.

**Warboss Imbad Ironskull**

Mewiththeface wrote:Also, if they have no planet, food can't regrow on the planet.

Food can't re-grow on the planet as it is? once the Tyranids are done with it it's a lifeless rock with no atmosphere or water. Without those things life can't come back to the planet.

**Warboss Imbad Ironskull**

Requia wrote:They'll replenish with time actually (volcanic activity releases a lot of both), though I don't know that nids plan a billion or two years in advance.

Volcanic activity dosen't release water unless it opens up underground rivers or lakes which then evaporate do to the heat, the water that woulden't evaporate has either been consumed by the Nids or boiled away due to the lack of an atmosphere that previously protected it from the sun.

Volcanic activity may release gas but not enough to re-create an entire atmosphere and even if it did have time to build up enough to be stable there woulden't be any water at that point which is essential to life. Without an atmosphere and direct contact with space the planet would cool, the core would die and stop spinning, when the core stops spinning the electromagentic field surround the planet dies causing the surface to be bombarded with radiation.

The planet would litterally be dead and would never have life again. Why do you think the Moon is lifeless and has no atmosphere or enternal heat. When it says that it's a barren lifeless rock it means it's a barren lifeless rock, planets have to walk a very tight balancing act to be able to support life and the only reason so many of them do in 40k is because the Old Ones engineered them to. So no the planets devoured by the Tyranids will not re-grow life.

Automatically Appended Next Post:

-Loki- wrote:Metals and minerals are consumed, broken down into their base chemicals. They leave rock behind, nothing else.

Metals are essential to life forms. We do happen to have iron in our own blood, afterall.

edit - bad wording

Trace amounts of Iron. We get the minerals in our bodies as transfer from what we eat either directly from plants or from the animals that ate the plant. We don't eat metal or rock and so the Tyranids woulden't need to eat it to get essential minerals because they would get it as transfer from the bio matter they harvest which is easier to break down then billions of tons of rock and metal.

The Tyranids don't consume entire planets because the energy gained would not be greater then the energy spent.

**Warboss Imbad Ironskull**

Medium of Death wrote:Can Tyranids kill a planet completely? Shutting down the core, stopping its magnetic field?

By cause and effect yes they can. I was hoping I didn't have to go through this but here it is.

The Tyranids remove all biomatter and the majority of water from a earth like planet, the flora which once converted carbon dioxide into oxygen are now gone (also remember that oceans produce oxygen to).

The build up of Carbon Dioxide eats through the ozone letting increased amounts of radiation break through the atmosphere. This combined with the heat already trapped by the Carbon Dioxide would increase the temperature of atmospheric gases, as their molecules began moving faster the gases escape velocity would increase which would allow them to escape the planets gravitational pull causing the atmosphere (composed of various gases at various temperatures and densities) to slowly bleed off into space.

Then the reverse happens. As gases bleed off there is less and less atmosphere, since there is less atmosphere the temperature of the planet starts to drop because it is gases that trap healthy amounts of radiation (and heat) which keep a planets surface warm.

As the temperature of a planet drops eventually the molten material at it's center will start to harden and prevent the core from spinning either entirely or partially. If the planets core is no longer spinning or spinning at a slower rate then the planets electromagnetic feild will be gone, what little water that may have been left on the planet would be frozen pockets trapped deep inside the planets mantel.

By this point those gases that where dense enough to stick to the planet based off gravity alone are gone because if a core stops spinning the planet also loses momentum in it's rotation lessening some of the planets gravitational pull (the same principle as G-forces pulling you down into your seat when on a roller coaster) so it's no longer strong enough to hold the gases.

So now the planet has become a cold, barren and iradiated rock with no atmosphere, very little water and no way of supporting life. It is a dead planet, and while this woulden't happen instantly and the time period that this happened in would depend on the size and density of the planet it would happen alot quicker then the time it took for a planet to "re-grow" life. So yes Tyranids can kill a planet if they're invasion is successfull.

Here is a quote directly from the codex which describes a planet after a Tyranid invasion

Kryptman found a blasted and sterile planet, now unrecognisable as the teeming ocean world it had once been. The planet had been sucked dry, every scrap of vegetation and every drop of water consumed

**Warboss Imbad Ironskull**

Who was that in response to?

**Warboss Imbad Ironskull**

We know what you're asking and it's been answered, the Tyranids don't just swallow whole planets because they have no need to. The amount of energy spent digesting so much mass would be greater then the energy gained from eating it.

And the problem with your theory is if there was just a huge bug that swallowed entire planets why would they need a scouting force, something that big woulden't send out scouting forces to devour the biomass of every planet only to come along and eat a barren hunk of rock. Something that big would just drift through space untill it found a planet and it would consume it since there would be nothing that could stop it.

**Warboss Imbad Ironskull**

Rochronos wrote:Dominatrix!

Not sure why you brought this up since it isn't large enough to eat a planet whole