Meet arach

A group of arachnotrons turn toward the player with intent to kill in MAP07: Dead Simple, in Doom II.

The arachnotron is a spider-like monster introduced in Doom II. It is quite similar to the spiderdemon but smaller and with large eyes that change color depending on the monster's current state (moving, hurt, or attacking). It is supported by a metal chassis and his body consists primarily of a large brain, along with two small arms. Instead of a chaingun it wields a powerful plasma gun that fires bursts of yellow and green energy.

According to the manual: Maybe cybernetics wasn't such a great idea after all. Look what the demons have done with it. It seems unfair somehow you're not the only guy in Hell with a plasma gun.

In Doom II, they make their first appearance in Dead Simple, where the player must fight them when they reinforce the fallen mancubi.

Combat characteristics

An arachnotron makes a crescendoing mechanical cry (sounds like a machinery powering-up) when spotting a player. Once the arachnotron engages an enemy it will continue to fire until the enemy moves out of its field of view or until the monster flinches in pain or is destroyed. Similar behavior can be observed with the spiderdemon, nazi soldier and the heavy weapon dude. When they die, their heads explode into a morass of gore as their mechanical bodies collapse while unleashing a dying tone that resembles failing machinery.

Tactical analysis

Although they may seem slow, arachnotrons are actually faster than quite a few of the other monsters and can catch up with the player at an alarming rate. They have a medium pain chance, so rapid fire weapons such as the chaingun will work well, although using the chainsaw on them is very risky. Their attacks are easier to avoid than the rapid-fire hitscan attacks of heavy weapon dudes and spiderdemons, but their plasma bursts are among the fastest projectiles, and their high rate of fire can quickly drain the player's health. Additionally, the plasma bursts can obscure the player's vision upon a successful hit. If a player constantly attacks, moves in broad side-to-side movements, and tries to get out of the arachnotron's line of fire periodically, then the player will sustain minimal damage.

Because of their sustained, extremely fast rate of fire, they are often more than capable of defeating almost any monster if provoked via monster infighting, especially when multiple Arachnotrons attack; however, stronger enemies such as a baron of hell will usually prevail in smaller battles because of their higher health.


  • As with the spiderdemon, the term arachnotron (roughly translatable as "spider instrument") is not absolutely literal, as they only have six limbs; two arms and four mechanical legs. Arachnids (spiders and such), on the other hand, have eight limbs. Curiously, while the Doom 64 version increases their leg count to six, they lack the arms.
  • In the Doom source code the internal name for the arachnotron is MT_BABY, and the root of its sprite name in the IWAD is BSPI, so the monster was arguably called (or nicknamed) baby spider during the development of Doom II.


ID #68 (decimal), 44 (hex)
Hit points500
Speed12 map units per frame
(140.0 map units per second)
Reaction time8
Pain chance128 (50%)
Pain time6 tics
Bits list

1: Obstacle

2: Shootable

22: Affects Kill %

Sprites & sounds
Sprite nameBSPI
Alert soundDSBSPSIT
Chase soundDSBSPWLK
Action soundDSBSPACT
Pain soundDSDMPAIN
Death soundDSBSPDTH
Ranged attack
Speed25 map units per tic
(875 map units per second)
Shots per minute263
Sprite nameAPLS (in flight)
APBX (impact)
SoundDSPLASMA (firing)
DSFIRXPL (impact)

Damage done by each plasma burst

Shots needed to kill Mean Standard
Min Max
Player (100%
health, no armor)
Player (100%
health, security armor)
Player (200%
health, combat armor)
Wolfenstein SS2.750.7825
Lost Soul5.021.0938
Commander Keen5.021.0938
Boss Brain211.681.70816
Pain Elemental18.272.041322
Hell Knight22.802.241728
Baron of Hell45.163.093652
Spider Mastermind134.412.61128140

  1. This table assumes that all calls to P_Random for damage, pain chance, impact animations, and backfire checks are consecutive. In real play, this is never the case: counterattacks and AI pathfinding must be handled, and of course the map may contain additional moving monsters and other randomized phenomena (such as flickering lights). Any resulting errors are probably toward the single-shot average, as they introduce noise into the correlation between the indices of "consecutive" calls.
  2. Assumes that direct hits are possible, which does not occur in any stock map.
  3. Hardcoded exception to infighting negates damage (excepting indirect damage caused by exploding barrels).

Appearance statistics

In classic Doom, the arachnotron is first encountered on these maps:

Doom IIMAP07: Dead SimpleMAP07: Dead SimpleMAP07: Dead Simple
TNT: EvilutionMAP06: Open SeasonMAP08: MetalMAP04: Wormhole
PlutoniaMAP03: AztecMAP03: AztecMAP03: Aztec

The IWADs contain the following numbers of arachnotrons:

Doom II154164
TNT: Evilution295257

Other games

Doom 64

Sshot arachnotron64

Doom 64's arachnotron in action.

In Doom 64 their physicality is considerably altered; the mechanical body is much bigger, with the brain head ducked down inside the machine itself instead of sitting atop it and the legs being longer and bent at upwards-pointing acute angles. Instead of a single plasma gun, the Doom 64 arachnotrons possess two guns that fire out two blue plasma bolt shots simultaneously, but done so in spurts of five instead of a constant rate of fire, though it will continue firing as long as it can see the player. They first appear in MAP14: Eye of the Storm unless the player goes through MAP30: The Lair and MAP32: Hectic, which contain arachnotrons but chronologically come first.

See also

Template:Sony PlayStation monsters

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