According to RAW for swarms,

A swarm can enter or move through an enemy’s space; this movement does not provoke opportunity actions.

I assume "pass through" in this case means "move into and out of as part of the same move action".

So if a swarm wants to move from one square adjacent to a Medium PC to another square adjacent to that same PC, all it has to do is pass through the PC's square first, right? And there are no consequences to doing so, unless someone else has an immediate interrupt they can use, or there's a status effect "can't/must move closer/farther". If not, the requirement to "pass through an enemy's square" can be ignored.

But, a swarm is subject to OAs normally when moving away (fleeing) from adjacent to a PC -- as long as it's not fleeing through another PC's square. Right?

Let me restate this. I have a question about interpreting this rule. There seems to be some ambiguity -- the rules don't say it clearly -- but the way I'm parsing them, when they say "moving into or through a PC's square does not provoke OAs" this immunity is not limited to OAs by the PC in question -- it's immune to all PCs' OAs. Period.

Am I right in my interpretation? Or has this been superseded by some errata?

For reference:


  • \$\begingroup\$ That is very strange. Moving away from a PC does not provoke an OA even if they are not the one whose square you are moving into. That doesn't compute to me. At the very least its worded vaguely. \$\endgroup\$
    – wax eagle
    Commented Jun 27, 2011 at 15:58
  • \$\begingroup\$ Yes it is worded vaguely @wax eagle, but what are you referring to? Moving out of any threatened square normally provokes an OA. \$\endgroup\$
    – Snowbody
    Commented Jun 27, 2011 at 16:16
  • \$\begingroup\$ Yes it does. That's the point. If I am standing in a square adjacent to a swarm which is also adjacent to one of my allies (or even an enemy) They can move away from me without provoking an OA or shifting, meaning I don't get a swing at it as it scurries off. As a defender I would be even more unhappy (already having trouble hitting it as its a swarm). \$\endgroup\$
    – wax eagle
    Commented Jun 27, 2011 at 16:25
  • \$\begingroup\$ @wax eagle, looks like this limited immunity to OAs was errata'd out, see the answer below. \$\endgroup\$
    – Snowbody
    Commented Jun 27, 2011 at 19:35

1 Answer 1


I believe this was corrected at some point. The "swarm" entry was published in 4 different books (MM, MM2, RC, and Monster Vault: Threats to Nentir Vale). The quotation you used appears to be from the Monster Manual. The compendium uses different wording:


A swarm is composed of multiple creatures but functions as a single creature. A swarm can occupy the same space as another creature, and an enemy can enter a swarm’s space, which is difficult terrain. A swarm cannot be pulled, pushed, or slid by melee or ranged attacks.

A swarm can squeeze through any opening large enough for even one of its constituent creatures. For example, a swarm of bats can squeeze through an opening large enough for one of the bats to squeeze through.

There's nothing there about opportunity attacks, so one would expect the rules to be followed as normal.

Note: The most recently published book is the Monster Vault, so I assume that is what the compendium uses.

  • \$\begingroup\$ Yes, it was the original wording, which is why I asked if it had been updated. I don't have D&DI. \$\endgroup\$
    – Snowbody
    Commented Jun 27, 2011 at 16:17

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