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Swarm of Bats 5e: Echolocation, Darkness and the 2024 Swarm
A swarm of bats is a CR 1/4 flying swarm with AC 12, a 30-foot fly speed, blindsight out to 60 feet and a bite for 5 damage (2d4). The 2014 swarm is Medium with 22 hit points and Echolocation: it can't use its blindsight while Deafened. The 2024 swarm is Large, has only 11 hit points, bites from 5 feet away and loses Echolocation and Keen Hearing. Its damage is low. What makes it dangerous is that it fights just as well in total darkness, so it's at its best paired with something that creates darkness.
Echolocation.The swarm can't use its blindsight while deafened.
Keen Hearing.The swarm has advantage on Wisdom (Perception) checks that rely on hearing.
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 bat. The swarm can't regain hit points or gain temporary hit points.
Actions
Bites.Melee Weapon Attack: +4 to hit, reach 0 ft., one creature in the swarm's space. Hit: 5 (2d4) piercing damage, or 2 (1d4) piercing damage if the swarm has half of its hit points or fewer.
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.
Walk 0, fly 30. It never lands. Blindsight 60 feet means darkness, fog and invisibility don't hide anything within 60 feet of it. Keen Hearing gives Advantage on hearing-based Perception checks, so a party whispering in the next cave isn't as quiet as it thinks. Echolocation is the off switch: a Deafened 2014 swarm loses its blindsight.
The rest is the standard swarm package: shared spaces, no healing, resistance to bludgeoning, piercing and slashing (magic weapons too) and eight condition immunities. Its 2014 bite reaches only a creature in its own space and falls to 1d4 at 11 hit points or fewer.
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 bat. The swarm can’t regain Hit Points or gain Temporary Hit Points.
Actions
Bites.Melee Attack Roll: +4, reach 5 ft. Hit: 5 (2d4) Piercing damage, or 2 (1d4) Piercing damage if the swarm is Bloodied.
Stat block from the SRD 5.2.1 (2024 rules) by Wizards of the Coast, licensed under CC-BY-4.0. Check an encounter with this monster in the encounter calculator.
2014 Swarm of Bats
2024 Swarm of Bats
Size
Medium
Large
AC / HP
12 / 22
12 / 11
Speed
0 ft., fly 30 ft.
5 ft., fly 30 ft.
Traits
Echolocation, Keen Hearing, Swarm
Swarm
Bites
+4, a creature in its space, 5 (2d4)
+4, reach 5 ft., 5 (2d4)
Three changes matter. Half the hit points: one Burning Hands (3d6) kills a 2024 swarm on a failed save half the time. Large size: it takes up a 10-by-10-foot area, so it can sit over two or three characters at once, though it still bites only one per turn. No Echolocation: deafening a 2024 swarm does nothing to its blindsight.
How Swarms of Bats Fight
Damage is not the point. +4 against AC 15 hits 50% of the time for 5, about 2.5 damage a round. Even four swarms deal only about 10 a round between them. Use bats for confusion, not for killing.
Darkness is the point. Blindsight works in magical darkness, which darkvision doesn't. Put a swarm inside a Darkness spell and it still perceives everyone within 60 feet, while the characters inside can't see it, so it attacks with Advantage and they attack it with Disadvantage. In 2014, a drow can cast Darkness once a day. Darkvision doesn't see through that spell, the drow's included, so the drow cast it on the party and stay outside. Inside the sphere, the bats bite with Advantage while the characters swing at something they can't see.
Move the swarm, not the party. The swarm flies at 30 feet and can share any character's space. Have it settle on the character who's holding the light or casting the spell, then follow them when they move.
They go where the noise is. With Keen Hearing in 2014, bats find whoever is loudest. A fighter in clanking armor or a character shouting orders is the first target.
Called in by a vampire. In 2014, a vampire can use Children of the Night once a day to call 2d4 swarms of bats or rats (if the sun isn't up), which arrive in 1d4 rounds. That's the classic bat-swarm moment: a vampire fight that suddenly fills with bats.
Running a Swarm of Bats Encounter
Each swarm is worth 50 XP. Encounters for four characters:
The 2014 labels come from the Dungeon Master's Guide thresholds and group multiplier in our encounter calculator. The four-swarm row is a good example of the 2014 multiplier overrating weak creatures: four swarms that deal 2.5 damage each per round aren't a Deadly fight for most level 1 parties.
A better guide: one swarm per character is a nuisance that soaks up a round or two of spells. Bats really work as support for a creature that benefits from confusion and darkness.
How Players Beat a Swarm of Bats
•Deafen a 2014 swarm.Blindness/Deafness (Constitution save, +0) deafens it, and Echolocation then turns off its blindsight. With no other special senses listed, in darkness it can't see at all. A Silence spell does the same to every bat swarm inside it. This trick doesn't work on a 2024 swarm.
•Blind it in 2024. Against a 2024 swarm, where Deafened does nothing, choose Blinded: the condition gives attacks against it Advantage and its own attacks Disadvantage. Its blindsight still tells it where everyone is.
•Area damage.Burning Hands and Thunderwave kill a 2024 swarm (11 hit points) on a failed save about half and a third of the time, respectively, and wound a 2014 swarm badly. Shatter's 10-foot radius covers a whole Large swarm.
•Light doesn't help much. Blindsight doesn't care about light. Light helps the party see the bats, which is all it does.
•Shut a door, then check it. The swarm fits through any opening a single bat could, so only a tight door or a stuffed gap keeps it out. A closed, sealed room gives a hurt party time to recover.
Swarm of Bats Encounter Ideas
The bell tower. A village bell tower hasn't rung in years because the belfry is full of bats. The party needs the bell rung as a signal. Climbing the tower's ladder in the dark with two swarms around them is the challenge, and ringing the bell sends the whole colony out at once.
The drow ambush. A tunnel narrows to a 10-foot passage. Two drow wait beyond it with two swarms of bats from a nearby roost. When the party enters the passage, one drow casts Darkness and the bats fly in. The party is stuck in darkness with bats biting them and drow crossbows coming from somewhere.
The vampire's warning. Before the party ever meets the vampire, a swarm of bats roosts wherever they camp, every night, and leaves before dawn. It never attacks. Following it back leads to the vampire's lair. Killing it tells the vampire someone noticed, because its bats stop coming home.
Frequently Asked Questions
What CR is a swarm of bats?
CR 1/4, worth 50 XP. The 2014 version has AC 12 and 22 hit points; the 2024 version has AC 12 and 11 hit points.
How does Echolocation work?
In the 2014 rules, a swarm of bats can't use its blindsight while it is Deafened. Without blindsight it has no special senses, so deafening it in darkness leaves it unable to see. The 2024 swarm doesn't have this trait.
Is a swarm of bats Medium or Large?
The 2014 swarm is Medium. The 2024 swarm is Large, so it covers a 10-by-10-foot area.
Can a vampire summon swarms of bats?
Yes, in the 2014 rules. The vampire's Children of the Night action calls 2d4 swarms of bats or rats once a day while the sun isn't up, and they arrive in 1d4 rounds.
What's the difference between a bat and a swarm of bats?
A single bat is a CR 0 Tiny beast with 1 hit point that's mostly useful as a familiar or a scout. A swarm of bats is a CR 1/4 creature that resists weapon damage and can share a character's space, so it's the version to use when bats should be a combat threat.
Stat blocks: System Reference Document 5.1 (2014) and 5.2.1 (2024), 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.