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Swarm of Centipedes 5e: The Swarm That Paralyzes Instead of Kills
A swarm of centipedes is a CR 1/2 Medium swarm of Tiny beasts with AC 12, 22 hit points, a 20-foot walk and climb speed and a +3 bite for 10 piercing damage (4d4). Its stat block has one rule that changes the whole fight: a creature it drops to 0 hit points is stable but poisoned for 1 hour, even after regaining hit points, and paralyzed while poisoned in this way. The centipedes don't kill their victims. They leave them helpless on the floor, and healing alone doesn't get them back up.
Swarm.The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a Tiny insect. The swarm can't regain hit points or gain temporary hit points.
Actions
Bites.Melee Weapon Attack: +3 to hit, reach 0 ft., one target in the swarm's space. Hit: 10 (4d4) piercing damage, or 5 (2d4) piercing damage if the swarm has half of its hit points or fewer. A creature reduced to 0 hit points by a swarm of centipedes is stable but poisoned for 1 hour, even after regaining hit points, and paralyzed while poisoned in this way.
Stat block from the SRD 5.1 (2014 rules) by Wizards of the Coast, licensed under CC-BY-4.0. Check an encounter with this monster in the encounter calculator.
SRD 5.1 prints the centipede swarm under the swarm of insects as one of its "Insect Swarms" variants. Apart from the poison rule, it's the base swarm: blindsight 10 feet, a climb speed, and a bite that only reaches a creature in its space and falls to 2d4 at 11 hit points or fewer. It follows the standard swarm rules: shared spaces, no healing, resistance to bludgeoning, piercing and slashing (magic weapons too) and immunity to eight conditions, grappled and restrained included.
The 2024 Replacement
There's no centipede swarm in SRD 5.2.1. Use the 2024 Swarm of Insects and choose a Climb Speed (its speed reads "20 ft., Climb or Fly 20 ft. (GM's choice)"). That version has AC 11, 19 hit points, a 5-foot reach and a bite for 6 Poison damage. It has no paralysis rider. If the paralysis is the reason you want centipedes, use the 2014 block.
How Swarms of Centipedes Fight
The bite is ordinary. +3 against AC 15 hits on a 12 or better, 45% of the time, about 4.5 damage a round. Against a level 1 wizard with 7 hit points, one average hit (10) drops them, straight into the poison.
The drop is not. When the swarm takes someone to 0 hit points:
•The character is stable. No death saves, as long as nothing damages them.
•The character is poisoned for 1 hour and paralyzed while poisoned this way.
•Healing brings back hit points but not mobility. A Healing Word wakes the character up, still paralyzed, for the rest of the hour.
Then comes the danger. Under the 2014 rules, a stable creature that takes any damage stops being stable and suffers a failed death save, two if the damage came from a critical hit. Attacks against a paralyzed creature have Advantage, and any hit from within 5 feet is a critical hit. A centipede swarm in a paralyzed character's space that keeps biting can kill in two hits. The stat block doesn't say whether it keeps feeding. DM ruling, not rules text: the swarm moves on to the next creature that's still moving, which makes the swarm a "take them alive" monster and lets you run it without killing anyone outright.
Climbing helps. A 20-foot climb speed lets the swarm come down walls and out of cracks. Start it on the ceiling of a narrow tunnel and drop it on the second character in the marching order.
Running a Swarm of Centipedes Encounter
Each swarm is worth 100 XP. Encounters for four characters:
The 2024 budget calls every row Low. The poison makes centipedes more dangerous than that. Every character who goes down is out for an hour, not a round. Under the 2014 Dungeon Master's Guide guidelines our encounter calculator applies, even two swarms are Hard for a level 1 party.
The best use is in a place where losing an hour matters: a collapsing mine, a ritual on a timer, or a monster nest where paralyzed characters have to be dragged out while more things arrive.
How Players Beat a Swarm of Centipedes
•Cure the poison, not just the wounds.Lesser Restoration ends the poisoned condition, which ends the paralysis, and Protection from Poison neutralizes the poison in both editions. Bring one of them into centipede country.
•Pull fallen characters away. A paralyzed character inside the swarm's space is in danger. Drag or carry them out of it and keep the front line between them and the swarm.
•Area damage and Wisdom saves.Burning Hands and Thunderwave hit hard against 22 hit points. Its Wisdom is 7 (−2), so Spirit Guardians at DC 13 deals full damage 70% of the time.
•Poison works on it. The swarm has no poison resistance. Cloudkill rolling down a tunnel works well against it.
•Don't count on control. Grapples, Entangle and webs don't hold a swarm, because it's immune to grappled and restrained.
Swarm of Centipedes Encounter Ideas
The paralyzed miners. Three miners lie in a side tunnel, alive and paralyzed. The party reaches them by finding the same swarm that got them. Getting four helpless people up a ladder shaft while centipedes come out of the walls is the real challenge.
The kobold trap.Kobolds keep a clay pot full of centipedes over a narrow passage. When it breaks, the swarm drops onto the party. Then the kobolds come in to drag away anyone who's paralyzed, alive, for ransom.
The cursed sarcophagus. A tomb's sarcophagus is full of centipedes. Whoever opens it gets a swarm in their space. The swarm itself isn't the worst thing in the tomb: a ghoul waits in the next room, and it would very much like a paralyzed meal.
Frequently Asked Questions
What CR is a swarm of centipedes?
CR 1/2, worth 100 XP. It has AC 12, 22 hit points, and a bite that deals 10 (4d4) piercing damage, or 5 (2d4) at half its hit points or fewer.
What happens when a swarm of centipedes drops you to 0 hit points?
You're stable, but poisoned for 1 hour even after you regain hit points, and paralyzed while poisoned this way. Lesser Restoration or another effect that ends the poisoned condition also ends the paralysis.
Is the swarm of centipedes in the 2024 rules?
No. The 2024 SRD has one Swarm of Insects with a Climb or Fly Speed chosen by the DM. With a Climb Speed it works as a centipede swarm, but it has no paralysis effect.
What's the difference between a giant centipede and a swarm of centipedes?
A giant centipede is a single CR 1/4 Small creature with a poison bite. A swarm of centipedes is CR 1/2, resists weapon damage, shares its victims' spaces, and leaves the creatures it drops paralyzed for an hour.
Stat blocks: System Reference Document 5.1 (2014), Wizards of the Coast, CC-BY-4.0. Tactics, encounter math and ideas are Loreify's own.
This page includes material from the System Reference Document 5.1 and 5.2.1 by Wizards of the Coast LLC, available under the Creative Commons Attribution 4.0 International License. Loreify is not affiliated with Wizards of the Coast.