The Tyranids Last Home was The Magellanic Clouds - An Updated Argument

Back in March 2012 I posted a small hypothesis about where the Tyranids might actually have come from.

My argument then was fairly simple: the Tyranids were explicitly extragalactic, yet the various Hive Fleets appeared to be attacking the Milky Way from rather different directions. In particular, some of them appeared to be arriving along the plane of the Galaxy whilst Leviathan was doing something rather different and coming up from below it. 

My suggestion was Galactic Cannibalism. I argued (rather vaguely) that the Tyranids had originated in one of the satellite galaxies associated with the Milky Way: the Large Magellanic Cloud, Small Magellanic Cloud, or Sagittarius Dwarf. Their interaction with the Milky Way could then potentially account for Tyranid populations arriving from apparently different directions. Fourteen years later, I think I had part of this right and part of it wrong. 

The original post is here: Tyranids from Galactic Cannibalism? 

First, a bit of astrophysical housekeeping. The Hubble expansion argument in the original post isn’t especially relevant here. The Magellanic Clouds are members of the Local Group and are gravitationally interacting with the Milky Way. Treating their separation as though it were simply increasing according to Hubble’s Law isn’t appropriate. Likewise, the idea that destruction of a satellite galaxy could simply scatter Tyranid populations around the Milky Way is a little too convenient. Sagittarius is being tidally disrupted. The Magellanic Clouds are a more complicated dynamical system and I wouldn’t make quite the same argument now. 

So let me modify the hypothesis. The Tyranids came from the Magellanic Clouds! 

Or, more precisely, the Large and/or Small Magellanic Clouds were the last galaxies consumed by the Tyranids before they turned their attention to the Milky Way. There are several reasons why I rather like this version. The first is Hive Fleet Leviathan. The modern Tyranid background has doubled down considerably on the strange geometry of Leviathan. It isn’t simply another fleet entering through the Eastern Fringe. Leviathan is enormous, with tendrils detected throughout the Imperium, and Imperial observers conclude that these tendrils are attacking from below the Galactic plane.

The Fourth Tyrannic War makes the point even more strongly. Tyranid fleets are now appearing in Segmentum Pacificus, on the western side of the Imperium, having emerged from beneath the Galactic plane. This changes how I think about the old problem. We don’t necessarily have Hive Fleets arriving at the Milky Way independently from several completely different external galaxies. Instead, Leviathan appears to represent an enormous Tyranid distribution beneath the disc which is intersecting the Galactic plane in multiple places. 

Now look at the Magellanic Clouds. The Large Magellanic Cloud lies at Galactic coordinates approximately l = 280.5 degrees b = -32.9 degrees and the Small Magellanic Cloud at l = 302.8 degrees b = -44.3 degrees. In other words, both are substantially below the Galactic plane.

That isn’t proof of anything of course! Half of the extragalactic sky is below the plane! But it is interesting. If we wanted a nearby extragalactic location from which a vast Tyranid swarm could approach the Milky Way from beneath the disc, the Magellanic system is sitting in exactly the right general part of the sky. 

There is then the big piece of Tyranid lore that didn’t exist when I wrote the original article: the Pharos. The epilogue of Pharos established that the destruction/overloading of the Pharos during the Horus Heresy attracted the attention of the Tyranids. At that point they were drifting in the intergalactic void. The Pharos flare effectively told them that there was something worth eating over here. At first sight, that seems to kill my 2012 suggestion. If the Tyranids were happily living in the Large Magellanic Cloud in M31, they weren’t drifting around in the intergalactic void waiting for the Pharos to go off. 

But there is a much cleaner version. Suppose they had already eaten the Magellanic Clouds. They consume their way through one or both galaxies, exhaust the useful biomass, move out into the surrounding void, and enter whatever passes for dormancy in a Hive Fleet. Then the Pharos lights up. Suddenly there is a beacon coming from the next major galaxy. Dinner. This even works reasonably well in terms of distance. The Large Magellanic Cloud is around 163,000 light years away. The Small Magellanic Cloud is around 200,000 light years away. There are approximately ten thousand years between the Horus Heresy and the arrival of the major Tyranid invasions in M41. A very crude straight-line calculation therefore requires an effective velocity of order 16-20 times the speed of light. Which obviously doesn’t work in real physics. Fortunately the Tyranids aren’t using real physics. Narvhal bio-ships create compressed-space transit corridors which allow Hive Fleets to cross interstellar distances faster than light. A journey from the Magellanic system to the Milky Way over that sort of timescale therefore causes no particular difficulty within the established setting. 

There is one consequence of this idea that I particularly like. The Magellanic Clouds should still be there in M41. Tyranids don’t eat stars. An observer in the Milky Way would therefore still see the Large and Small Magellanic Clouds hanging in the southern sky. From a distance they might look entirely normal. But send a ship there and things could be very different. Billions of stars. Planetary systems intact. Rocky worlds still orbiting their suns. And almost nothing alive. World after world reduced to sterile rock, stripped of atmosphere, oceans and accessible organic material. An entire pair of dwarf galaxies that constitute the Tyranids’ previous meal. There is also a potentially testable version of all of this. Take the canonical locations where Leviathan’s tendrils enter the Galactic disc and try to reconstruct their approximate three-dimensional approach vectors. Then compare those with the real direction of the Magellanic system. Games Workshop’s Galactic cartography obviously isn’t accurate enough for precision astronomy. But the test doesn’t need to be precise. If the Leviathan vectors consistently occupy the Galactic hemisphere and broad direction containing the Magellanic Clouds, the idea becomes rather more interesting. 

If they point everywhere beneath the disc, the correspondence is probably coincidence. So my revised hypothesis for 2026 is slightly different from the one I proposed in 2012: The Tyranids didn’t necessarily originate in the Magellanic Clouds. The Magellanic Clouds were simply the last galaxies they ate. Afterwards they moved into the void. 

Then somebody turned on the Pharos. Oops.