Enemies

At the time, Factorio has three types of enemies: Biters, Spitters and Worms.

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Biters

Biters are one of two main antagonists in the game. They are the native inhabitants of the extraterrestrial world and commonly live peacefully with worms and spitters. Biters are arthropods living in organic nests. They come in 3 sizes: small, medium and big. In the beginning of each freeplay game there will only be the small ones, with increasing pollution they will become bigger, related to the enemy's evolution. Biters are attracted by and enraged by pollution and will attempt to destroy its sources. They prefer to attack the player character, turrets and logistic robots and will stop searching for pollution if they can see and attack any of those. Biters deal physical damage.

Picture	Name	Info
File:SmallBiter-anim.gif	Small Biter	Weakest of biters, can be easily killed with a pistol. Health: 15
File:MediumBiter-anim.gif	Medium Biter	Stronger and slower than the small biter. Can pose a problem for and even kill weaker players. Health: 75 Resistances: Explosion 0/10% Physical 4/0%
File:BigBiter-anim.gif	Big Biter	Very resistant and dangerous, nearly immune to gunfire. Can attack through walls and hit objects directly behind them. Health: 375 Resistances: Explosion 0/10% Physical 8/0%

Spitters

Spitters are much like Biters. The only difference is - except their appearance - that they only have got a ranged attack. They spit at any opponents (e.g. players) with an acid projectile that can neither be dodged nor deal damage to anything else than the original target. Commonly the acid resistance of any buildings (like a turret) and armor is much less than its physical resistance. Because of this Spitters deal more average damage than Biters. Their behavior and sizes are very similar to the Biter ones, except their health and resistances.

Picture	Name	Info
File:SmallSpitter.png	Small Spitter	Weakest of spitters. Easy to kill with any weapon, but attacks at range. Health: 10
File:MediumSpitter.png	Medium Spitter	Stronger and slower than the small version. Can pose a problem for and even kill weaker players. Attacks at range, making it dangerous for turrets. Health: 50 Resistances: Explosion 0/10%
File:BigSpitter.png	Big Spitter	Very resistant and dangerous, can take much damage. Attacks at range, making it dangerous for turrets. Health: 200 Resistances: Explosion 0/30%

Worms

The Worms are natural allies of Biters and Spitters and will attack you if you get close enough. They act like static turrets and will not follow you.

Like any other enemy, worms come in 3 sizes, their power increasing with size. Unlike Biters and Spitters, Big and Medium Worms can be created directly after start of a new game. Their appearance is not dependent on time. (see http://www.factorioforums.com/forum/viewtopic.php?f=23&t=6454)

Picture	Name	Description
File:SmallWorm.png	Small Worm	A weak worm. Still not easy to kill though. Health: 200
File:MediumWorm.png	Medium Worm	Medium worms are very dangerous to even more advanced players. They should be handled with care. Health: 350 Resistances: Explosion: 5/15% Physical: 4/0%
File:BigWorm.png	Big Worm	Big worms are the most powerful enemy in factorio. They deal a high damage and are almost immune to common gunfire of any sort. Health: 500 Resistances: Explosion: 10/30% Physical: 8/0%

Spawners

Picture	Name
File:Nest.gif	Biter's Nest
File:Spitternest.gif	Spitter's Nest

Evolution

The game evolution factor is a global variable that determines what kind of biters will be spawned. You can check the variable in the dev console:

game.player.print(game.evolutionfactor)

It goes from 0 (not evolved at all) to 1 (maximal evolution). At the moment the evolution factor can only increase. This evolution factor is increased by three kinds of events:

• The passage of time very slightly increases the evolution factor.
• The production of pollution (globally) increases the evolution factor.
• Destroying the enemy spawners significantly increases the evolution factor.

All these values are set in mapsettings. There they can also be changed / modded.

Current (0.9.1) default settings are:

-- percentual increase in the evolution factor for 60 ticks (game second)
game.player.print(game.mapsettings.enemy_evolution.time_factor

0.000008

-- percentual increase in the evolution factor for 1000 Pollution Units
game.player.print(game.mapsettings.enemy_evolution.pollution_factor)

0.00003

-- percentual increase in the evolution factor for every destroyed enemy spawner
game.player.print(game.mapsettings.enemy_evolution.destroy_factor)

0.005

The percentages are applied on the base of (1 - current_evolution_factor). So for instance destroying the enemy spawner in the beginning of the game results in increase of evolution factor by 0.005 (half a percent) while doing this when the evolution factor is 0.5 the increase is only 0.0025 (quarter a percent).

As of 0.9.1 the biter spawning is done probabilistically based on the current evolution. Lets imagine a wheel - the "spawning wheel". We will be slicing that wheel as a cake. Small biters take the first 0.3 part of the wheel, medium ones the middle 0.3 part and big biters take the last 0.4. When a biter is about to be spawned the random point on the wheel is selected limited by the current evolution. So in theory while the evolution is below 0.3 there should be only small biters, then slowly medium ones will enter and in the end the big ones. The composition of the biter animation in the end should be 0.3-0.3-0.4. There is one more factor called the spawn_shift - this is a mechanism when the further away from the starting location the more the "rolling of the wheel" is shifted towards one. That means that if the shift is 0.2 for instance that at the time when evolution factor is 0.25 the result for spawning is actually 0.2 + 0.25 = 0.45 and a medium biter might be spawned.

Besides choosing what kind of biter will be spawned the evolution also influences the spawning interval. As of 0.9.1 this interval (spawning_cooldown in the enemy-spawner definition) is interpolated between 360 (0 evolution) and 150 (1 evolution) ticks.

All the values for the spawner (distribution of the biters based on evolution, the spawning shift, spawning_cooldown, etc.) can be modded from the data.

Expansions

Sometimes a small group of biters will leave their base to create a new base. This group will search for a suitable spot that's about 3 chunks away from existing biter bases and 3 chunks away from any of your buildings. Once they have found a suitable spot the group of biters dies and forms a new base. This new base will first be very small (about one spawner and a few worms) but will get some additional spawners within a small area as time passes. This base-wide expansion is somehow limited (the blog says something about 7, but that doesn't seem to match reality in some cases).

--Shadowblink (talk) 22:48, 31 August 2014 (CEST)

Acid Damage

Worms and spitters deal acid damage. Despite how it looks, those projectiles can neither deal damage to units other than the target nor can be dodged.

Picture	Name
	Worm's animation

--Trucario (talk) 14:01, 7 October 2013 (CEST)