When Do Biters Attack?
Once your first factory starts producing, pollution spreads and biters take notice. Biters attack when:
- Pollution reaches their nest (they become angry)
- You destroy a nest (immediate retaliation)
- Evolution factor is high enough (time + pollution)
Peaceful mode: Even without biters attacking, you still need to clear nests to expand. Walls help protect your builders.
The Minimum Viable Defense
Step 1: Stone Wall (Priority 1)
Place stone walls in a rough circle around your base. 1 tile thick is enough for the first few hours.
Cheap: Stone walls cost only stone bricks
Effective: Biters cannot destroy stone walls quickly
Step 2: Gun Turrets (Priority 2)
Place gun turrets every 5-8 tiles along the wall. They need ammo (firearm magazines or piercing rounds).
| Turret Type | Ammo | DPS | Notes |
|---|---|---|---|
| Gun turret | Firearm magazine | Low | Early game only |
| Gun turret | Piercing rounds | Medium | Upgrade ASAP |
| Laser turret | Electricity | High | Mid-game power hungry |
Step 3: Ammo Management
Use steel chests next to each turret, fed by inserters from a central ammo belt.
Critical: If your turrets run out of ammo, they are just decoration. Set up a dedicated ammo production line early!
Pollution Management (Defense by Reducing Aggression)
Biters attack because of pollution. Reduce pollution = fewer attacks.
| Method | Effect |
|---|---|
| Efficiency module 1 in miners | Minus 30 percent pollution |
| Efficiency module 2 in labs | Minus 45 percent pollution |
| Solar panels | Zero pollution power |
| Nuclear power | Near-zero pollution, massive output — see Nuclear Power Guide |
| Burning excess wood | Plus plus pollution (don't do it) |
Defense Upgrade Path
The upgrade order as your factory grows:
Stone Wall right arrow Gun Turrets (firearm mags)
down arrow
Steel Wall right arrow Gun Turrets (piercing rounds)
down arrow
Laser Turrets (electricity powered, no ammo)
down arrow
[Flame Turrets](https://factorioguides.com/defense/flamethrower-defense-guide/) (area damage, fuel-based)
down arrow
Artillery Turrets (long range, explosive shells)
Next: Defense Guide Overview — all defense layers explained.