Before we get started here, I just want to thank Wizards for correcting this from the 2014 Monster Manual’s Swarm of Poisonous Snakes. Remember: if you bite it and you die, it’s poisonous. If it bites you and you die, it’s venomous.

Is it petty and pedantic? Yes it is.

You’re welcome.

There’s a lot of great use for swarms of creatures in D&D, and especially swarms of slithering, venomous serpents. Snakes have been used to signal fear in storytelling for countless generations, and you’ll be leaning on millennia of tradition to really get your players skin crawling. Your ancient temples, surprise traps, dank sewers – all of these environments are a great place to put these creatures, and they’ll make sure your players never let their guard down.

In a tactical sense, swarms are an interesting challenge to deal with. Like all Swarms, the Swarm of Venomous Snakes can occupy the same space as another creature, a trick that other, more unitary monsters cannot achieve. This means that you can drop them from the ceiling on top of someone, have them at the bottom of a pit trap, or just slither them out of holes in the walls and not just surround your players, but overwhelm them.

Ask Indiana Jones about how much fun it is to be covered in snakes.

While it isn’t strictly an attribute of swarms, by the way, I think it would not be unreasonable to institute a little homebrew rule under the right circumstances: if an attacker rolls between the Swarm’s AC (14) and the friendly target’s AC, have the ally take half damage. You need to be precise enough with your strike to hit the snakes and not your friend. This isn’t a rule – just an idea to make swarms more terrifying in a fight.

And remember that Swarms – of Snakes or anything else – aren’t thinking creatures. You can’t reason with them or trick them or outsmart them. Go ahead. Try convincing a hundred sets of fangs to stand down. They come at a player like a force of nature, and a character can either run or get ready to be overwhelmed.

That really should be your goal with the Swarm of Venomous Snakes when you put them into an environment. You want your players to be a little freaked out as you describe these many-colored serpents crawling all over them, maybe into their armor or around their ankles, fangs flashing. Having done so, your players should look at every shadowed nook and cranny with suspicion and fear. If that happens, then you’ve done your job as a DM.

There is a sense in which Swarms of Snakes are a kind of betrayal, as well. The players go into a place thinking they know the terrain – stone, mud, dirt – and suddenly it becomes something else. Suddenly the terrain itself is alive, and that might be a good way to subtly cue your players in to the idea that they can’t trust the place they’re in. This overgrown ancient pyramid may look like just another mossy pile of stones, but lurking within it is an environment beyond the players’ reckoning. Use your Swarm to hint to them that they can’t trust their preconceptions as they move further into the adventure.

On a more thematic, symbolic level, you can also use a Swarm of Snakes to hint at corruption or blight. Something happened here in this ancient desert stronghold that has turned everything slightly wrong. Lean in to the less charitable connotations of snakes in legend and folklore, and have these deliverers of poison and terror slither in and out of every nook and cranny, surrounding your players and turning their own blood against them.

In other words, don’t just describe what the Snakes look like or how they feel. Make it clear what they mean in this place and this context. Make the metaphor into a real thing, a creeping dread that surrounds them on all sides.

Whatever happened in this place long ago has made everything go bad, and that’s what your players are here to solve.

Bonus points if that Bad Thing turned everyone into snakes. That Walk of Shame as your players leave the temple and look at the slashed and broken bodies of dozens of Swarms of Snakes will, I hope, give them pause.

Not every encounter has to be a big fight against a personal enemy. Some fights can have their roots right in the deepest parts of the brain, the ancient signals that go off when you’re surrounded by snakes, and all you can think is, “Get it off!”