In Terraria, enemies, critters, and other NPCs will spawn off-screen and enter the screen area based on their AI. The rate at which enemies are spawned, the maximum number of enemies, and the type of enemies spawned are all dependent on the time of day, biome, the tile type of the ground, and other factors.

Spawn rates[]

Basics[]

The game determines new enemy spawns every tick.^[1] There are two variables it takes into consideration when doing so: spawn rate and max spawns, with the spawn rate setting the chance of an enemy spawning at each tick, and the max spawns limiting the number of enemies that are active at a time.^[2]

The default spawn rate is 1/600.^[3] This means that for each tick, there is a chance of 1/600 that an enemy is spawned. Since there are 60 ticks in 1 second, there is a 9.52% chance that at least one enemy will spawn in a given second.

The default max spawns is 5.^[4] This means that a new enemy can only be spawned if the sum of the NPC slots of all current active enemies is lower than 5. Most enemies occupy 1 NPC slot by default; see the following table for a list of all enemies with a higher or lower number of NPC slots. Active enemies exclude many enemies considered part of the same enemy, for example, body and tail parts of worms, because a Giant Worm, which has 6–8 segments (i.e. individual enemies), would otherwise occupy a disproportionate number of NPC slots. Town NPCs are not considered active NPCs for the purposes of NPC spawning. See the following table for a list of enemies that are not considered active.

 NPCs with non-default NPC slots 

Maximum number of loops have been performed NPC NPC slots Big Stingy Hornet 1.21 Little Stingy Hornet 0.87 Big Spikey Hornet 1.16 Little Spikey Hornet 0.78 Big Leafy Hornet 1.1 Little Leafy Hornet 0.92 Big Honey Hornet 1.15 Little Honey Hornet 0.8 Big Fatty Hornet 1.25 Little Fatty Hornet 0.85 Big Raincoat Zombie 1.1 Small Raincoat Zombie 0.9 Big Pantless Skeleton 1.15 Small Pantless Skeleton 0.85 Big Misassembled Skeleton 1.13 Small Misassembled Skeleton 0.87 Big Headache Skeleton 1.07 Small Headache Skeleton 0.93 Big Skeleton 1.1 Small Skeleton 0.9 Big Female Zombie 1.05 Small Female Zombie 0.87 Demon Eye (Variant 2) 1.15 Purple Eye (Variant 2) 1.1 Green Eye (Variant 2) 0.85 Dilated Eye (Variant 2) 0.9 Sleepy Eye (Variant 2) 1.1 Cataract Eye (Variant 2) 1.15 Big Twiggy Zombie 1.08 Small Twiggy Zombie 0.92 Big Swamp Zombie 1.13 Small Swamp Zombie 0.87 Big Slimed Zombie 1.11 Small Slimed Zombie 0.89 Big Pincushion Zombie 1.13 Small Pincushion Zombie 0.93 Big Bald Zombie 1.15 Small Bald Zombie 0.85 Big Zombie 1.1 Small Zombie 0.9 Big Crimslime 1.15 Little Crimslime 0.85 Big Crimera 1.15 Little Crimera 0.85 Giant Moss Hornet 1.8 Big Moss Hornet 1.65 Little Moss Hornet 1.35 Tiny Moss Hornet 1.2 Big Stinger 1.2 Little Stinger 0.85 Heavy Skeleton 2 Big Boned 2 Big Eater 1.15 Little Eater 0.85 Eye of Cthulhu 5 Devourer Head 3.5 Eater of Worlds Head 5 Mother Slime 2 Fire Imp 3 Dark Caster 2 Cursed Skull 0.75 Skeletron Head 6 Bone Serpent Head 6 Cave Bat 0.5 King Slime 5 Jungle Bat 0.5 Piranha 0.5 Hellbat 0.5 Demon 2 Voodoo Demon 2 Spike Ball 0.3 Dungeon Slime 2 Blazing Wheel 0.3 Bird 0.4 Wyvern Head 5 Giant Bat 0.5 World Feeder Head 3.5 Angler Fish 0.5 Wall of Flesh 10 Retinazer 5 Spazmatism 5 Skeletron Prime 6 The Destroyer Head 5

 NPCs that are never considered active 

Devourer Body Devourer Tail Giant Worm Body Giant Worm Tail Eater of Worlds Body Eater of Worlds Tail Skeletron Hand() Bone Serpent Body Bone Serpent Tail Wyvern Legs Wyvern Body Wyvern Body 2 Wyvern Body 3 Wyvern Tail Digger Body Digger Tail World Feeder Body World Feeder Tail Wall of Flesh Wall of Flesh Eye The Hungry Leech Body Leech Tail Prime Cannon() Prime Saw() Prime Vice() Prime Laser() The Destroyer Head The Destroyer Body The Destroyer Tail Probe Golem Head Left Golem Fist Right Golem Fist Free Golem Head Plantera's Hook Creeper Pumpking Blade Blue Cultist Archer White Cultist Archer Martian Saucer() Martian Saucer Turret() Martian Saucer Cannon() Moon Lord's Head Moon Lord's Hand Moon Lord's Core True Eye of Cthulhu Vortex Pillar Mysterious Tablet Lunatic Devote Lunatic Cultist Target Dummy Dutchman Cannon() Stardust Pillar Nebula Pillar Solar Pillar Eternia Crystal (NPC) Mysterious Portal Betsy Dark Mage(T1) Dark Mage(T3) Etherian Goblin(T1) Etherian Goblin(T2) Etherian Goblin(T3) Etherian Goblin Bomber(T1) Etherian Goblin Bomber(T2) Etherian Goblin Bomber(T3) Etherian Wyvern(T1) Etherian Wyvern(T2) Etherian Wyvern(T3) Etherian Javelin Thrower(T1) Etherian Javelin Thrower(T2) Etherian Javelin Thrower(T3) Old One's Skeleton(T1) Old One's Skeleton(T3) Wither Beast(T2) Wither Beast(T3) Drakin(T2) Drakin(T3) Kobold(T2) Kobold(T3) Kobold Glider(T2) Kobold Glider(T3) Ogre(T2) Ogre(T3) Etherian Lightning Bug

Natural spawn rates[]

Spawn rate and max spawns have set values, which are different depending on the environment. They are formally defined for the environments mentioned in the following tables. Events that are not listed usually employ separate mechanisms to control spawn rates; bosses usually occupy enough NPC slots to block most other spawns.

Pre-Hardmode[]

Biome/Event/ Boss fight	Surface			Underground	Cavern	Underworld
	Day	Night	[5]
Forest Desert Snow biome[6]	1/600 5	1/360 6	1/108 10	1/300 8	1/240 9	1/600 10
Jungle	1/240 7	1/144 9	1/60 15	1/120 12	1/96 13	n/a
Corruption Crimson	1/390 6	1/234 7	1/70 13	1/195 10	1/156 11	n/a
Dungeon	n/a	n/a	n/a	1/90 14	1/72 15	n/a
Meteorite[7]	1/240 5	1/144 6	1/60 11	1/120 8	1/96 9	n/a
Sandstorm	1/540 6	1/324 7	1/97 12	n/a	n/a	n/a
Underground Desert	1/120 15	1/72 15	1/60 15	1/60 15	1/60 15	n/a
Goblin Army	1/20 10 + 1.5 per player			n/a	n/a	n/a
Wall of Flesh fight	n/a	n/a	n/a	n/a	n/a	1/1800 3
Hallow[8]	1/600 5	1/360 6	1/108 10	1/300 8	1/156 11	n/a

Hardmode[]

Biome/Event/ Boss fight	Surface			Underground	Cavern	Underworld
	Day	Night	[5]
Forest Desert Snow biome[6]	1/540 6	1/324 7	1/97 12	1/243 10	1/216 11	1/540 12
Jungle	1/216 9	1/129 10	1/60 15	1/97 15	1/86 15	n/a
Corruption Crimson	1/351 7	1/210 9	1/63 15	1/157 13	1/140 14	n/a
Dungeon	n/a	n/a	n/a	1/72 15	1/64 15	n/a
Meteorite[7]	1/216 6	1/129 7	1/60 13	1/97 11	1/86 12	n/a
Sandstorm	1/216 9	1/129 10	1/60 15	n/a	n/a	n/a
Underground Desert	1/108 15	1/64 15	1/60 15	1/60 15	1/60 15	n/a
Goblin Army Frost Legion Pirate Invasion Martian Madness Lunar Events	1/20 10 + 1.5 per player			n/a	n/a	n/a
Wall of Flesh fight	n/a	n/a	n/a	n/a	n/a	1/1620 3
Hallow	1/540 6	1/324 7	1/97 12	1/243 10	1/140 14	n/a

Additionally, the spawn rate will be modified by the number of active enemies in the area. The fewer active enemies there are, the faster new ones will spawn:

• If the sum of the NPC slots of all active enemies is lower than 20% of max spawns, the denominator of the spawn rate will be multiplied by 0.6.
• If the sum of the NPC slots of all active enemies is lower than 40% and greater than or equal to 20% of max spawns, the denominator of the spawn rate will be multiplied by 0.7.
• If the sum of the NPC slots of all active enemies is lower than 60% and greater than or equal to 40% of max spawns, the denominator of the spawn rate will be multiplied by 0.8.
• If the sum of the NPC slots of all active enemies is lower than 80% and greater than or equal to 60% of max spawns, the denominator of the spawn rate will be multiplied by 0.9.

(Note that all products are rounded down to the nearest integer.)

The following table lists some examples for this mechanic. It is to be read in the following way: If the natural spawn rate and max spawns (as determined from the overview above) and sum of the NPC slots of all active enemies are equal to the values in the first three columns, then the spawn rate is altered as shown in the last column.

Manual alteration of spawn rates[]

Certain items can be used to change the spawn rate and max spawns when used or placed, as per the following table. All effects are multiplicative rather than additive.

Item	Spawn rate factor[9]	Effective spawn rate	Max spawns
Water Candle(also if held)	1/0.75	+33%	+50%
Battle Potion	1/0.5	+100%	+100%
Calming Potion	1/1.3	−23%	−30%
Sunflower	1/1.2	−17% ( only)	−20%
Peace Candle(also if held)	1/1.3	−23%	−30%
Invisibility Potion( only)	1/1.2	−17%	−20%

These effects do not stack with themselves, i.e., a single Water Candle, Peace Candle, or Sunflower has the same effect as multiple of each one.

Water and Peace Candles cancel each other out, even though they do not alter spawn rates by the same absolute values. If both are active (e.g. a Peace Candle is held while a Water Candle is placed nearby), none is applied.

There is one exception to this: Water Candles placed (explicitly not held) in Space^[10] always increase spawn rates, regardless of nearby Peace Candles. Their effectiveness depends on nearby Peace Candles, however:

Item	Spawn rate factor[9]	Effective spawn rate	Max spawns
Water Candleplaced in Space (with no Peace Candle held or placed nearby)	1/0.375	+167%	+50%
Water Candleplaced in Space (with a Peace Candle held or placed nearby)	1/0.5	+100%	+50%

In addition, nearby Fairies have the same effect as Sunflowers and Invisibility Potions, reducing the effective spawn rate by 17% and decreasing the max spawns by 20%.

Up to this point, spawn rates cannot be increased to fractions greater than 1/60 and max spawns cannot be increased to values greater than 15. Both will be cut off there. The spawn rates and max spawns of the invasion events listed in the tables above are exempt from this. There is no lower limit for spawn rates and max spawns.

Effect of town NPCs on spawn rates[]

The presence of nearby town NPCs generally reduces spawn rates and max spawns. This effect is adjusted in the Underworld and in Graveyards.

When 3 or more town NPCs or the Skeleton Merchant are present nearby, no enemies will spawn. This is only valid for areas outside of the Underworld and Graveyards, and only for Classic worlds – in Expert Mode, there is still a 3.33*1/30 (3.33%) chance an enemy may spawn that tick. Enemies from events as well as bosses (and their servants) will bypass this restriction.

Journey Mode[]

Spawn rates can be manually altered in Journey Mode, from 0× (disabling spawns) to 10× the normal rate. Even with the spawn rate set to 0×, bosses may still be summoned, mining up Tombstones can still cause Ghosts to spawn, and certain Celestial enemies can spawn.

Spawn locations[]

Each player in the game will spawn their own enemies. If two players are in the same area, monsters will appear twice as fast as they would with only one player. Max Spawns rule are still used, which means that even if 2 players are in the same spot, you cannot gather 30 normal monsters near the spot. (Don't forget, the bats count as 1/2, and some special enemies count as 2 or more.)

Choosing a spot to spawn the enemy[]

^Verify When the game decides to spawn an enemy, it will first choose a random tile within a rectangle around the player (specifically, the tile containing the top left corner of the player's hitbox). The maximum distance from the player it can choose from is 84 tiles east, 83 west, 46 up, and 45 down. If the picked tile is a solid block, it will try another one. Tiles that are actuated out do not count as solid. If the picked tile has a player-placed wall that blocks enemies from spawning, it will also try another tile.

Once an empty tile is found, it moves down until it finds the ground. (Note that this tile can be more than 45 tiles below from the player. If it finally is outside the "Active Rectangle" it will be instantly despawned, anyway.) If there is enough space for an enemy to be spawned at this location, this will be the tile it chooses. The exception to this is when the player is in an area where Harpies and many other flying enemies can be spawned. In this case, the game does not attempt to find a ground tile.

The chosen tile is then checked to make sure it is not within the "safe" area around the player. It cannot be within 62 tiles east or west, or 34 tiles up or down. Also, the chosen tile space must be completely outside 2088 × 1172 pixel rectangles centered on the center of each player's hitbox. (If the player is not riding a mount, the top edge of this is 34 + 3/16 tiles above the top left corner tile mentioned above, meaning that NPCs can spawn on ground exactly 35 tiles above a player standing on half blocks, but not a player standing on full blocks.)

Using certain items causes monsters to spawn further out than normal. Equipping a Rifle Scope or Sniper Scope does so only when the player has a compatible gun selected, whether or not the player is zoomed out.

Note : If using the Depth Meter, Compass, or similar, each tile is equal to 2 feet, so double all measurements to get distances in feet

On the  Mobile version (pre-1.4 only), the no-spawn area around the player is 68 by 48 tiles, and the spawn area is 112 by 62 tiles. In addition, enemies cannot spawn closer than 34 tiles to the sides and 24 tiles up and down. They also cannot spawn farther than 56 tiles to the sides and 31 tiles up and down.

Choosing a type of enemy to spawn[]

The type of enemy spawned will depend on many factors including, but not limited to:

• Time of day
• Weather (e.g., Angry Nimbus and Ice Golem require Rain/Blizzard)
• Depth
• Distance East or West (Ocean enemies, Martian Probes, Goblin Scouts, etc.)
• Player's Current biome (Corruption, Meteor, Jungle, etc., in the case of most biome-specific flying enemies)
• Tile the enemy spawns on (Jungle Grass, Ebonstone, Marble, etc. in the case of most biome-specific grounded enemies)
• Wall behind the player (Lihzahrd Brick Wall, Dungeon Brick Wall, etc.)
• Wall behind the enemy's spawn location (Dungeon Brick Wall variants)
• Special events (Blood Moon, Solar Eclipse, invasion events, etc)
• Randomness

Notes[]

• When standing on the left or right edge of the world, the enemies can spawn on screen, as long they are at least 62 tiles from the player. The screen is around 85 blocks wide, so in this case the enemies can spawn in the farthest quarter of the screen. (This may not necessarily be the case, some players have larger screens, as big as 120 blocks wide).
• Equipping Binoculars does make the active rectangle bigger.

History[]

 PC version

• Desktop 1.4.0.1:
  • Added the following enemies to the list of NPCs that are never considered active: Skeletron Hand, Prime Cannon, Prime Saw, Prime Vice, Prime Laser, Martian Saucer, Martian Saucer Turret, Martian Saucer Cannon, and Dutchman Cannon.
  • Increased the natural spawn rates and max spawns in the Dungeon:
    • Increased spawn rates in the Underground layer from 1/120 (pre-Hardmode) and 1/97 (Hardmode) to 1/90 (pre-Hardmode) and 1/72 (Hardmode).
    • Increased spawn rates in the Cavern layer from 1/96 (pre-Hardmode) and 1/86 (Hardmode) to 1/72 (pre-Hardmode) and 1/64 (Hardmode).
    • Increased max spawns in the Underground layer in pre-Hardmode from 13 to 14.
  • Increased the natural spawn rates and max spawns in the Underground Desert:
    • Increased spawn rates on the surface during the day in pre-Hardmode from 1/180 to 1/120.
    • Increased spawn rates on the surface during the night in pre-Hardmode from 1/108 to 1/72.
    • Increased spawn rates in the Underground layer in pre-Hardmode from 1/90 to 1/60.
    • Increased spawn rates in the Cavern layer in pre-Hardmode from 1/72 to 1/60.
    • Increased max spawns on the surface to 15. The old max spawns were 10 (pre-Hardmode) / 12 (Hardmode) during the day, and 12 (pre-Hardmode) / 14 (Hardmode) during the night. Max spawns in the Underground Desert are now 15 at all times and under all conditions.

• Desktop 1.2.4: Fixed bug where spawn rates would increase underground when a moon event is happening.

• Desktop 1.2.3: Fixed bug where spawn rates were higher than intended everywhere rather than when below the middle of dirt layer.

References[]