Friday Facts #445 - The Biters Bite Back | Factorio

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Friday Facts #445 - The Biters Bite Back

Posted by<br>Klonan<br>on 2026-08-07

Hello,

We have another dose of human generated facts for you.

I was planning to write about these biter and enemy behavior changes before the 2.1 release, but an unfortunately timed neck injury led to it being postponed.

The silver lining here is that now I can write about all the player reactions and funny bugs we've found along the way.

We might be getting into controversial territory here, but I like the biters and I like fighting them. I like clearing<br>nests when expanding. I especially like defending against them when they smell my success.

However I never had fun with the expansion groups.

The whole feature just didn't seem to land right, and I would like<br>to know if many other players agree — so let's delve right in.

Enemy expansion planner

The enemy expansion planner is one of those systems that has been around for a very long time (2013), and while it has had its improvements and fixes over time, it never really received a holistic review of how it was working in the modern context of the game.

Expansion groups were too small, making for weak, ineffective expansions

While we tuned and balanced map generation to make the nests a challenge, the expansion planner only ever sent small sorties to expand.

Small expansion nests do not really create a challenge, they just annoy the player and create busywork. It would feel much more compelling and meaningful to have one large expansion nest rather than 10 tiny ones, so I decided to move in that direction:

Increase group size with evolution factor.

Modify group size dependent on the map generator biter base size.

The goal with the changes, is that at any point in the game, an expansion party would be sized to present a good challenge at your current technology level.<br>Another guiding principle was to try to get the expansion nests to match existing ones, so that you can't tell which were from the map generation and which were from the expansions.

The numbers in the initial 2.1.0 release seemed a bit too strong (Experimental Biter expansion too strong), so in 2.1.13 I have tuned back the numbers:

2.1.0 expansion size vs Evolution factor

2.1.13 expansion size vs Evolution factor

(For those wondering, a graph for 2.0 would be a straight line from 5 to 20)

In short, the bases will start smaller (from 20 down to 10), but scale to the same max size of 80. The game picks a random number between the min and max when dispatching an expansion group. You can also notice the variance between min and max was reduced in 2.1.13.

There was also a bug causing the groups to settle a little bit too close to the factory walls (Expansion party worms spawn too close to wall and destroy defenses) which I fixed for 2.1.13, so there should be less pressure in this regard.

Exploring early would nerf expansions

The expansion planner time between expansions didn't scale with the number of candidates. So if you had a lot of candidates somewhere far away, then you wouldn't get any expansions near your base. This led to an unfortunate inverse difficulty relationship:

Players who explored around the map early would experience fewer expansions near their factory.

Biter nests in explored territory would 'thicken' and become much denser than intended.

To solve this, I did a mostly fresh rewrite of the heuristic and penalties for the candidate chunks, trying to ensure that areas explored but otherwise untouched by the player wouldn't have an effect on the expansion behavior. You can see the difference below:

Expansion candidates before (left) vs. after (right)

Greener = Higher probability.

The result is that not only do we have significantly fewer candidate chunks, but that they are more relevantly placed close to open areas or areas the player has cleared before. Expansions should now feel more predictable as well, the timing and pressure should be more consistent.

Another part of the rewrite was to untangle some subtle biter related assumptions, which were causing problems with the Pentapods on Gleba (Pentapod Expansion Broken).

Build base behavior

The expansion planner tells a group of biters when and where to go and build a base, but the actual building was carried out by a unit group with a 'Build base' command. Similar to the expansion planner, there were many subtle assumptions and hardcoded numbers throughout the logic, and the functional difference before and after is hard to explain.

The most noticeable change is to the cooldown between building the entities.

Beforehand this was calculated as 5 ticks per hitpoint of built entity, which sounds nice but effectively made the biters act inconsistently...