Stellaris Brain Slug Event Guide [2023]

Brain Slug Stellaris Event Cover

Stellaris is a game of discovery and anomalies are of utmost importance when it comes to exploration. Every so often, there are some that are stranger than others, like the Stellaris Brain Slug anomaly event, which we will discuss in this article. Brain Slugs have been in the game since Distant Stars Stellaris DLC. The event is triggered by a level 4 Anomaly called Abandoned Settlements. As soon as you research it, the Broken Union events will follow.

“Let’s all go to the Brain Slug Planet and just walk around not wearing a helmet.”Futurama

A Broken Union – First Step of the Brain Slug Event

Broken Union event started - Brain Slug Stellaris event part 1
Printscreen: Broken Union event, Stellaris

Broken Union is the first part of the Brain Slug event. The event starts with you finding out that there was an intelligent reptilian species living on the planet. A long time ago they were “devoted from a tool-making agrarian society into mere beasts“. How you may wonder – well it seems that once they were connected to a neural symbiont and that’s what uplifted their civilization. The reasons why this connection was disrupted are unclear, and if you want to proceed with the event, you have to issue a Special Project “Neural Symbiont Study“.

Unraveling Brain Slugs – Neural Symbiosis Study

Printscreen: Neural Symbiosis event part 2 of Brain Slug Event Chain in stellaris game
Printscreen: Neural Symbiosis event, Stellaris

The Neural Symbiosis Study is finished quickly (it’s going to take just over a month) and the next part of the event will be revealed. Your Science Officer will try to experiment on strange Brain Slugs and even introduce them to various animal hosts. As reptilians were once pre-FTL civilization, they are the first choice. Soon other species will be the subject of the experiment but it just won’t work since the symbionts will only accept a certain kind of host – a willing one.

A more radical approach is the solution – your science officer will offer himself as a host for a neural slug. If you deny his request you will get a one-time major bonus for Society Research and Stellaris Brain Slug event will end. This is not recommended and is the “boring” ending.

Printscreen from Stellaris: Neural Symbiosis event - part 2 of Brain Slug Stellaris event
Printscreen: Neural Symbiosis event part 2, Stellaris

As it turns out, your Science Officer was right – the Brain Slugs connection was successful and you get more prologue on what happened with the previous hosts. It seems that the Brain Slugs are hivemind symbiotes with lifespans of hundreds of years, and their past union with reptilians came to an end when their hosts grew suspicious of them and tear them apart.

You can choose if you want to modify all the pops on your planet after this.  Before you do that, let’s check out what bonuses Stellaris Brain Slugs bring.

Brain Slug Host Trait Analysis

Brain Slug Host trait printscreen from Stellaris
Printscreen: Brain Slug Host trait, Stellaris

Firstly, you will get a massive science bonus – 10% for Physics, Society, and Engineering Research. Secondly, you will get the leader Brain Slug Host Trait as well, which means that these bonuses will multiply. Unity from Jobs will increase by 10% but the biggest downside is Pop Growh Speed -25% debuff.

As you can see, this is an interesting situation – major technology bonuses for population growth debuff is the exchange. You will have to make a decision based on your needs at the moment, but keep one thing in mind: Brain Slugs won’t affect your entire population unless you genetically modify them. You can use this to your advantage depending on when the Stellaris Brain Slug Event occurred.

  • Early game: you should keep your Brain Slugs confined to their planet of origin
  • Mid-game: if you can, genetically modify the species on science worlds in order to boost the research and minimize the downside of Brain Slug Trait
  • Late Game: usually at this point you want to avoid further population growth so Brain Slugs can be of great use

Another piece of advice worth listening to is that Brain Slugs Trait has an awesome synergy with Psionic Trait as both of them boost research and stack one onto one another.

Are Brain Slugs Worth It?

In most cases, Brain Slugs’s science research bonus is worth taking no matter the debuff, in terms of population growth. There are other means of getting your population speed growth increased and you can always confine the Brain Slugs into just one planet. If you combine it with other traits like Psionic, you will get a major boost in your Tech Research speed and usually, that’s the most important thing in Stellaris. Exploring anomalies is fun, but wrecking and countering your opponent’s fleet is even more satisfying, so check out our Stellaris ship design guide in order to optimize your naval power.


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