In Factorio, your factory does not grow in a vacuum. Every belt you lay and every furnace you fire pumps pollution into the world, and that pollution is exactly what wakes up the planet’s native life and turns it against you. The biters — Nauvis’s swarming insectoid wildlife — are the single most consistent threat to a long-running base, and learning how they think is the difference between a thriving megabase and a smoking crater. This guide breaks down every enemy type, the sizes you’ll face, the evolution mechanic that makes them stronger over time, and the full defensive toolkit you’ll use to hold the line. We’ll flag the differences between the older 1.1 line and the current Factorio 2.0 + Space Age release (both launched October 21, 2024) wherever they matter.
Meet the Enemies: Biters, Spitters, and Worms
On Nauvis (the home planet) there are three core hostile types, and understanding the role each plays is the foundation of every good defense.
- Biters — the classic melee chargers. They rush your walls and structures in packs and attack at close range. Numbers are their weapon: a single biter is trivial, but a swarm will chew through an unprotected base fast.
- Spitters — ranged attackers that hurl acid. Beyond the direct hit, their acid leaves a damaging puddle on the ground that lingers and continues to hurt anything standing in it, including your turrets and walls. Their range means they can hit your defenses from outside your turrets’ reach if you’re not careful.
- Worms — stationary, turret-like creatures embedded in enemy bases. They don’t move, but they deal high damage with splash and act as the entrenched artillery of a nest. When you push into enemy territory to clear it, worms are usually what punishes a sloppy approach.
All of these come from spawners — the “biter nests” and “spitter nests” that dot the map. Spawners actively produce new units and define the footprint of an enemy base. Destroy the spawners and you destroy the base’s ability to regenerate. That said, killing spawners has a major downside we’ll cover below in the evolution section, so it’s never a “free” action.
Four Sizes: Small to Behemoth
Each enemy type — biter, spitter, and worm — comes in four sizes: small, medium, big, and behemoth. As you progress, the small variants that plagued your early base are gradually replaced by larger, tougher, harder-hitting versions. A behemoth biter is a different beast entirely from the small one you swatted in hour one: more health, more damage, and faster. Which size spawns is governed almost entirely by the evolution factor, explained next.
| Type | Role | Sizes | Key threat |
|---|---|---|---|
| Biter | Melee charger | Small → Medium → Big → Behemoth | Swarm numbers, closes distance fast |
| Spitter | Ranged acid | Small → Medium → Big → Behemoth | Leaves damaging acid puddles; outranges weak defenses |
| Worm | Stationary turret | Small → Medium → Big → Behemoth | High damage + splash; defends nests |
Pollution: Why the Biters Are Coming for You
Here is the central truth of biter behavior: enemies stay passive until your factory’s pollution reaches their nests. A nest that has never tasted your pollution cloud will sit there doing nothing. The moment your spreading pollution touches a spawner, that spawner begins “spending” the pollution to muster attacks against the source — your factory.
Attacks come in waves rather than a constant stream. Roughly speaking, an attack is mustered about every 1 to 10 minutes at random once a nest is being polluted, with the size of the attack tied to how much pollution the spawner has absorbed. This has a profound strategic implication: your pollution footprint is a dial you control. Every smelter, every assembler, every burner you run adds to the cloud. The electric furnace, for example, produces 1 pollution per minute — small per unit, but it adds up across hundreds of machines.
This is exactly why efficient power and smelting choices double as defensive choices. Switching dirty burner setups to cleaner electric production, using efficiency modules, and building solar fields all shrink the cloud that’s drawing aggression. If you want to dig into the cleanest ways to power a base — and how to keep biter aggression low by minimizing emissions — see our comprehensive guide to power management in Factorio, and our deep dive on smelting for furnace efficiency.
The Evolution Factor: How Biters Get Stronger
Every Factorio save tracks a single hidden number called the evolution factor, ranging from 0 to 1. At 0, only small biters exist; as it climbs, medium, then big, then behemoth variants begin to spawn. This number only ever goes up during normal play, and three things drive it:
- Time passage — a small, constant trickle. Simply playing the game slowly raises evolution even if you never expand.
- Pollution produced — the more you pollute over the life of the save, the faster evolution rises. Yet another reason to keep emissions in check.
- Spawner kills — the single strongest driver. Every nest you destroy bumps evolution noticeably. This is the counterintuitive trap: aggressively wiping out enemy bases to “secure the perimeter” actively makes the surviving biters stronger.
A “squashing” formula in the math keeps evolution from easily hitting a perfect 1.0 — the closer it gets to the top, the harder each additional point is to add — but make no mistake, on a long campaign you will face behemoths. The practical takeaway: don’t clear nests you don’t need to clear. Expand deliberately, keep your pollution cloud tight, and only push into territory you intend to occupy and defend. Killing spawners purely for tidiness is one of the most common ways new players accidentally fast-track their save into a behemoth nightmare.
Building Your Defenses
Factorio gives you a layered defensive toolkit. The best perimeters combine all of these — walls to absorb melee, turrets to deal damage, and gates to let you and your trains through without leaving a hole.
Walls and Gates
Walls are your first line of physical defense. They have high health, block enemy movement, and force biters to stop and chew rather than walking straight into your machines. A wall alone won’t kill anything, but it buys your turrets time to do the killing. Gates are walls that open automatically when you (or a train) approach and close behind you, so you can route roads and rail lines through a solid perimeter without leaving a permanent gap. The standard pattern is a double or triple wall layer with turrets set back just behind it.
Gun Turrets
Gun turrets are the cheapest, earliest defense. They’re ammo-fed — you load them with magazines (and ideally automate ammo delivery via belt or logistic bots so they never run dry during a wave). They’re effective early but consume a steady stream of ammunition, which means a supply line to keep them stocked. Many players belt piercing rounds straight to their perimeter turrets for exactly this reason.
Laser Turrets
Laser turrets are electric and research-gated — you have to unlock them, and then they draw power instead of ammo. The huge advantage is logistics: no ammo belts, no restocking, just a strong enough power grid. The trade-off is that a large laser wall is a heavy electrical load, especially during a sustained attack, so your power infrastructure (and your accumulator buffer) needs to keep up. This is yet another place where solid power management directly protects your base.
Flamethrower Turrets
Flamethrower turrets are fluid-fed (you pipe crude or light oil to them) and provide outstanding area denial. They lay down burning ground that scorches whole packs at once, making them devastating against the dense melee swarms that biters love to form. A common late-game perimeter is a flamethrower line backed by laser turrets: the flames soften and burn the swarm while the lasers pick off survivors and spitters.
| Turret | Feed | Availability | Best against |
|---|---|---|---|
| Gun turret | Ammo magazines | Early game | General-purpose early defense |
| Laser turret | Electricity | Research-gated | Low-maintenance walls; spitters at range |
| Flamethrower turret | Fluid (oil) | Mid–late game | Dense melee swarms; area denial |
Keep Your Walls Repaired
Defenses take damage, and a half-destroyed wall is an invitation. The cleanest solution is automated repair: stock repair packs in your roboport network and construction robots will fly out and patch damaged walls and turrets automatically after a wave passes. Each repair pack restores 600 health total. For the full mechanics of passive repair and how to set it up, read our guide on how to repair structures in Factorio, and our breakdown of construction and logistic robots for keeping turrets ammo-stocked and walls rebuilt without micromanagement.
A Practical Defensive Doctrine
Pulling the mechanics together, here’s a defensive philosophy that holds up from your first wall to a sprawling megabase:
- Control your pollution. It’s both what triggers attacks and what fuels evolution. Efficient power and smelting are defensive investments.
- Don’t over-clear nests. Spawner kills are the strongest evolution driver — expand only as far as you’ll defend.
- Wall in layers. Walls absorb melee and create the kill zone; gates let your logistics through cleanly.
- Mix turret types. Flamethrowers for swarms, lasers for low-maintenance coverage and spitters, gun turrets as cheap early backbone.
- Automate restocking and repair. Belt or bot ammo to gun turrets; keep repair packs in the network so bots heal the wall after each wave.
- Watch the spitters. Their acid puddles and range punish defenses that are too far forward — set turrets back behind your walls.
One more thing worth automating early: a clean way to handle overflow ammo, oil barrels, and other clutter that piles up around a defended perimeter. If your inventory and chests are getting messy, our guide to deleting and managing items covers trash slots, deconstruction planners, and the classic chest-and-shoot void.
Factorio 2.0 & Space Age: New Enemies on New Worlds
Everything above describes Nauvis, and on Nauvis the biter/spitter/worm behavior is essentially carried forward from 1.1 with 2.0 tweaks. But the Space Age expansion (released alongside 2.0 on October 21, 2024, $35 for the DLC) adds four new planets and, with them, two entirely new enemy types that behave nothing like Nauvis biters.
Gleba: Pentapods
The jungle-swamp world of Gleba is home to the pentapods — the umbrella enemy type for that planet. They come in distinct forms:
- Wrigglers — melee pentapods that close in to attack.
- Strafers — ranged fliers that attack from a distance.
- Stompers — heavy melee bruisers that bring serious weight to an assault.
Pentapods are tied to Gleba’s unique spoilage-driven mechanics and demand a different defensive approach than the static-wall-and-turret line you’d build on Nauvis.
Vulcanus: Demolishers
The volcanic world of Vulcanus introduces demolishers — giant, regenerating worm-like creatures that patrol their own territory. They are not nest-spawned swarmers; they’re enormous individual monsters that require sustained, heavy firepower to bring down, and their regeneration means half-measures fail. Engaging a demolisher is a deliberate operation, not a perimeter-defense problem.
Fulgora and Aquilo
Not every new world fights back the same way. Fulgora has no conventional biter-style hostiles — instead it presents lightning hazards rather than nests, so defense there means lightning protection rather than walls and turrets. Aquilo likewise lacks the traditional nest-and-swarm enemy in the Nauvis sense. The key thing to remember: these are all Space Age additions. If you’re playing base-game 2.0 without the DLC, the biters, spitters, and worms on Nauvis are still the whole story.
Whether you’re holding a Nauvis perimeter against behemoth waves or coordinating a multiplayer push onto Gleba, a stable server makes the difference. Spin up your own always-on world with dedicated Factorio server hosting from XGamingServer, and check the Factorio server documentation for setup, mods, and configuration walkthroughs.
Frequently Asked Questions
What makes biters attack my factory?
Pollution. Enemies stay passive until your factory’s pollution cloud spreads far enough to reach their nests. Once a spawner is being polluted, it spends that pollution to muster attacks — roughly one wave every 1 to 10 minutes at random. Reduce your emissions and you reduce both the frequency and size of attacks.
What is the evolution factor and how do I keep it low?
The evolution factor is a hidden 0-to-1 number that controls how strong biters get — higher values spawn medium, big, and eventually behemoth variants. It rises from three things: time (a small constant), total pollution produced, and spawner kills. Spawner kills are the strongest driver, so the best way to keep evolution low is to limit your pollution and avoid clearing nests you don’t actually need to take.
What’s the difference between biters, spitters, and worms?
Biters are melee chargers that swarm in numbers. Spitters are ranged attackers that throw acid and leave damaging puddles on the ground. Worms are stationary, turret-like creatures with high damage and splash that defend enemy nests. All three come in four sizes: small, medium, big, and behemoth.
Which turrets are best for defense?
Use a mix. Gun turrets (ammo-fed) are cheap early defense. Laser turrets (electric, research-gated) are low-maintenance and great once you have the power. Flamethrower turrets (fluid-fed) excel at area denial against dense melee swarms. A strong late-game wall combines flamethrowers up front with laser turrets behind, all sitting behind a layered wall.
Are there new enemies in Factorio 2.0 / Space Age?
Yes. The Space Age expansion adds two new enemy types on new planets: pentapods on Gleba (split into wrigglers, strafers, and stompers) and demolishers on Vulcanus — giant regenerating worm-like creatures needing sustained heavy firepower. Fulgora has lightning hazards instead of nests, and Aquilo has no traditional swarm enemy. On Nauvis, biter behavior is essentially the same as in 1.1.
Should I rush out and destroy nearby biter nests?
Generally no — at least not for tidiness. Because spawner kills are the strongest evolution driver, clearing nests you don’t intend to occupy makes the remaining biters stronger faster. Expand deliberately, take only the territory you’ll defend, and let your walls and turrets handle the waves your pollution attracts.
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