Enemies

Enemies are creatures that want to harm the player. They normally come from spawners and begin on the enemy force. There are three types of enemies: Biters, Spitters and Worms. Each of these types comes in three stages of growth and thus strength.

Creatures

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 four sizes: small, medium, big and behemoth. 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 Damage: 6
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 Damage: 15 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 Damage: 30 Resistances: Explosion 0/10% Physical 8/0%
File:BehemothBiter-anim.gif	Behemoth Biter	Very resistant and dangerous, nearly immune to gunfire. Can attack through walls and hit objects directly behind them. Health: 5000 Damage: 100 Resistances: Explosion 10/20% Physical 8/20%

Combat

The biter class enemy will likely be the most common threat to a player's factory. While any attack can catch an undefended factory off guard, most players will be able to handle attacks from small biters with relative ease. Medium biters often pose a much greater threat though due to their heavy armor, not present on small biters. Big biters are another step in this direction and can come as another nasty shock to any player not familiar with their world's evolution level. Behemoth biters are a huge threat to any factory and serve as the Player's prime incentive to avoid excess pollution. However, Biters of any size can be managed by static defense, though some of the larger waves can be overwhelming.

Biters come fairly early to attack a factory that produces large amounts of pollution, as pollution will attract an attack. Once the pollution cloud reaches a nest, the player can expect biters to be showing up shortly. The attack group will be focused on destroying the source of the pollution, but will change targets as soon as one appears of higher priority, typically by level of pollution, though they target the player or static defense first and foremost. Biters also have the ability to find their way around a defense, to a degree. This can be used to partially control the movement of the biters allowing turrets longer to damage them, but requires the "bait" of this trap be left open. Biters aren't always willing to fall for the bait. Some biters will choose the most direct route and will attack the walls of the trap regardless making them less predictable and more dangerous.

Spitters

Spitters are much like Biters. The only difference, besides their appearance, is 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 Damage: 10
File:MediumSpitter.png	Medium Spitter	Stronger and slower than the smaller version. Can pose a problem for and even kill weaker players. Attacks at range, making it dangerous for turrets. Health: 50 Damage: 20 Resistances: Explosion 0/10%
File:BigSpitter.png	Big Spitter	The bulkiest of the spitters and so can take the most damage. Attacks at range, making it dangerous for turrets and the player. Health: 200 Damage: 30 Resistances: Explosion 0/30%
File:BehemothSpitter.png	Behemoth Spitter	The even more bulkiest of the spitters and so can take the most damage. Attacks at range, making it dangerous for turrets and the player. Health: 2000 Damage: 50 Resistances: Explosion 0/35%

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, but due to much greater range, in comparison to other enemies, will be able to inflict damage without leaving the nest. However, their static nature does render them more vulnerable to certain attacks.

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, and will not always spawn near spawners. Their appearance is not dependent on time. (see http://www.factorioforums.com/forum/viewtopic.php?f=23&t=6454)

Worms deal acid damage.

Picture	Name	Description
File:SmallWorm.png	Small Worm	A weak worm. Still not easy to kill though. Health: 200 Damage: 10
File:MediumWorm.png	Medium Worm	Medium worms are very dangerous to even more advanced players. They should be handled with care. Health: 350 Damage: 30 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 Damage: 60 Resistances: Explosion: 10/30% Physical: 8/0%

Picture	Name
	Worm's animation

Spawners

Picture	Name
File:Biternest-anim.gif	Biter's Nest	Health: 350 Resistances: Explosion: 5/15% Physical: 2/0%
File:Spitternest.gif	Spitter's Nest	Health: 350 Resistances: Explosion: 5/15% Physical: 2/0%

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.evolution_factor)

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 global Pollution Production increases the evolution factor.
• Destroying the enemy spawners significantly increases the evolution factor.

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

Current (0.12.4) default settings are:

-- percentual increase in the evolution factor per tick.
game.player.print(game.map_settings.enemy_evolution.time_factor

0.000004

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

0.000015

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

0.002

Pollution production is the total pollution produced by buildings per tick, not the pollution spreading on the map, so it is not reduced by trees or other absorbers. e.g. : 15 burner mining drills produce 150 pollution per second, raising the evolution factor by 0.00000225 per tick.

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.

Spawn chances by evolution factor

	Biter's Nest
Factor	Small Biter	Medium Biter	Big Biter	Behemoth Biter
0	100.0%
0.05	100.0%
0.1	100.0%
0.15	100.0%
0.2	100.0%
0.25	100.0%
0.3	100.0%
0.35	75.0%	25.0%
0.4	56.3%	43.8%
0.45	41.7%	58.3%
0.5	30.0%	70.0%
0.55	20.5%	79.5%
0.6	12.5%	87.5%
0.65	6.7%	77.8%	15.6%
0.7		66.7%	33.3%
0.75		50.0%	50.0%
0.8		33.3%	66.7%
0.85		28.6%	71.4%
0.9		25.0%	75.0%
0.95		22.2%	77.8%
1		12.5%	50.0%	37.5%

	Spitter's Nest
Factor	Small Biter	Small Spitter	Medium Spitter	Big Spitter	Behemoth Spitter
0	100.0%
0.05	100.0%
0.1	100.0%
0.15	100.0%
0.2	100.0%
0.25	100.0%
0.3	41.7%	58.3%
0.35		100.0%
0.4		100.0%
0.45		100.0%
0.5		100.0%
0.55		75.0%	25.0%
0.6		50.0%	50.0%
0.65		21.4%	64.3%	14.3%
0.7			75.0%	25.0%
0.75			62.5%	37.5%
0.8			50.0%	50.0%
0.85			37.5%	62.5%
0.9			25.0%	75.0%
0.95			22.2%	77.8%
1			12.5%	50.0%	37.5%

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).