The arachnotron is a cybernetic spider-like monster introduced in Doom II. It is structurally the same as the spiderdemon, but weaker, and much smaller in size. Its biological body consists primarily of a large brain with two small arms, and eyes that change color depending on the monster's actions. This body is seated into a metal chassis with four articulated hydraulic legs. Instead of the "super chaingun" of the spiderdemon, it wields a plasma cannon which fires sustained bursts of yellow and green energy projectiles. In Doom II, they make their first appearance in Dead Simple, where the player must fight them when they emerge to avenge the fallen mancubi.
An arachnotron makes a revving, mechanical shriek when alerted. Once the arachnotron locks on to an enemy, it will continue to fire plasma bursts until the target moves out of its field of view, the monster flinches in pain, or it is destroyed. Similar behavior can be observed with the spiderdemon, Wolfenstein SS, and the heavy weapon dude. When it dies, its head explodes into a morass of gore as the mechanical chassis collapses, unleashing a dying sound similar to malfunctioning machinery.
Although they may seem slow due to the speed of their animation frames, arachnotrons are actually faster than most other monsters and can reach the player's position at an alarming rate. They have a medium pain chance, so rapid fire weapons such as the chaingun will work well. Using the chainsaw on them is inadvisable due to their size, which prevents the attack from reliably connecting. 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. Use of the blur sphere only makes their attack erratic and difficult to avoid, and is thus not recommended.
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.
- The arachnotron's rate of fire is three times lower than that of the player's plasma gun.
- 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 baby spider during the development of Doom II. In a similar fashion to this name, the earlier developmental versions of the monster were more straightforward miniaturizations of the spiderdemon, with a similar palette and a chaingun attack, as shown in numerous pre-release screenshots.
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.
|Shots needed to kill||Mean|| Standard
health, no armor)
health, security armor)
health, combat armor)
|Baron of Hell||45.16||3.09||36||52|
- 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.
- Assumes that direct hits are possible, which does not occur in any stock map.
- Hardcoded exception to infighting negates damage (excepting indirect damage caused by exploding barrels).
The IWADs contain the following numbers of arachnotrons per skill level:
|Monsters from Doom and Doom II|
| Doom: Baron of Hell | Cacodemon | Cyberdemon | Demon | Imp | Lost soul | Shotgun guy | Spectre | Spiderdemon | Zombieman|
Doom 2: Arachnotron | Arch-vile | Commander Keen | Heavy weapon dude | Hell knight | Mancubus | Pain elemental | Revenant | Wolfenstein SS | Final boss
|Monsters from Doom 64|
|From Doom: Arachnotron | Baron of Hell | Cacodemon | Cyberdemon | Demon | Hell knight | Imp | Lost soul | Mancubus | Pain elemental | Shotgun guy | Spectre | Zombieman|
New: Marine | Mother demon | Nightmare imp