Enemies

At the time, Factorio has two types of enemies; Biters and Worms.

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Biters

Biters are the main antagonists in the game. They are the native inhabitants of the extraterrestrial world and commonly live peacefully with worms. Biters are arthropods living in organic nests. They come in 3 sizes: small, medium and big. 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
File:Sb.png	Small Biter	Weakest of biters, can be easily killed with a pistol.
File:Mb.png	Medium Biter	Stronger and slower than the small biter. Can pose a problem for and even kill weaker players.
File:Bb.png	Big Biter	Very resistant and dangerous, nearly immune to gunfire. Can attack over thin walls.

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Spawners

Picture	Name
File:Nest.gif	Biter's Nest

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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.

Worms

The Worms are the natural allies of the Biters and will attack you if you get close enough. Worms will act like static turrets and will not follow you. Like Biters, worms come in 3 sizes, their power increasing with size. Worms deal acid damage. Despite how it looks, worm's projectile can neither deal damage to units other than the target nor can be dodged.

Picture	Name
File:Sw.png	Small Worm
File:Mw.png	Medium Worm
File:Bw.png	Big Worm

Picture	Name
	Worm's animation

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