Swarms suck. In 5e, in Old School games - they just suck. A bee swarm is basically “a weird creature that takes up space.” Boring.
Let’s fix that.
The Problem With Standard Swarms
Look at a 5e Bee Swarm. You get hit points, stats, can’t grapple it, can occupy another creature’s space, fits through small openings. That’s… it. It’s just another monster with a slightly different shape.
Swarms should feel different. They should make players panic. They should behave like actual swarms.
Swarm Principles That Work
Here’s how to make swarms interesting for both 5e and OSR:
Use Hit Dice for everything. Every Hit Die the swarm has adds +1 to hit. A 5 HD swarm is +5 to hit. Simple, scary, scales automatically.
Damage scales with HD too. Set damage per Hit Die (like 1d4 per HD for bees). As the swarm takes damage and loses HD, its damage drops. The fight has momentum.
Swarms can merge. Two 3 HD swarms can combine into one 6 HD swarm. Suddenly that +6 to hit is a lot scarier than two +3s. Players will panic when they see swarms moving towards each other.
Example: Bee Swarm Rebuilt
- 5 hit points per Hit Die (4 base + 1 Con)
- 5 HD = 25 HP total
- +5 to hit (drops as HD drops)
- 1d4 damage per Hit Die
- DC 12 Con save or take extra poison damage per HD
The killer feature: ignores metal armour. Can you imagine plate armour against bees? They’re getting under it. The fighter’s AC means nothing. That changes behaviour immediately.
Track HP with 5 tokens on the table. Knock one off for every 5 damage. Dead simple, visually satisfying, everyone knows exactly how dangerous the swarm still is.
Example: Amoeba Swarm
Same principles, different flavour:
- 8 HD, 3 HP per die = 24 HP
- Acid damage
- Resistant to physical damage
Here’s the nasty twist: acid dissolves armour. Every successful hit reduces AC by 1d2 permanently. Rust monsters terrify players for this exact reason. Now your swarm does it too.
Rolling dice for the armour loss creates tension. Players watch that d4 hit the table knowing their plate might survive or might not.
Fighting Swarms: Player Options
Give players tools, but make them think:
- Ranged attacks: Disadvantage. You’re not shooting arrows at bees.
- Area of effect: Advantage. Fire, thunder, whatever hits everything at once.
- Blades: Disadvantage on damage (roll twice, take lower). Swinging steel at insects doesn’t work great.
- Fire: Double damage. Watch players drop their swords and grab torches.
- Critical fail when allies are in the swarm: You hit your friend. Don’t even roll attack - just roll damage. You’re swinging at their head because there’s wasps on it.
Why This Works
These rules make swarms feel like swarms:
- They merge and split
- They ignore certain defences
- They require different tactics
- They create real tension
And the maths stays simple. No complex tracking - just tokens on the table that everyone can see.
Bottom Line
Take these principles and apply them to any swarm creature. The specific numbers matter less than the unique abilities. Bees ignore metal armour. Amoebas dissolve it. Rats spread disease. Locusts destroy food supplies.
Make them behave differently. Make players change their tactics. Make swarms scary again.
This post came from a question by Adventures With Dice on the forums - if you’ve got something you’d like me to cover, ask in the Discord!