Movement and perception through Swarms

[Theo R Cwithin]

Are there any rules about movement and sighting through swarms?

Swarms never make attacks of opportunity, which I understand to mean that one can freely move into, through and out of a swarm without risking damage.

(1) From this I gather that one can charge, maintain concentration, etc, when moving through a swarm. True?

(2) Does moving through a swarm affect movement speed? (In other words, does it count as difficult terrain or something?)

(3) Does a (flying) swarm provide concealment, or in other ways affect vision (eg, to Spot checks, etc)?


The first question I infer from the RAW to be "yes"; just looking for confirmation. RAW doesn't discuss the other two AFAICT, so I'm guessing "no", but they seem to merit circumstance modifiers, at least in some cases; just wondering if there are official rulings in these instances.

 

[Ahnehnois]

I don't see any rules addressing these questions either. My thoughts:

1. Yes, unless difficult terrain prevents it. An intelligent swarm could ready an action and move to intercept a creature, which would cause damage at the end of that action, which could disrupt spellcasting.

2. I would rule that certain nonflying swarms count as difficult terrain, doubling movement costs and blocking charges and imposing skill penalties (tiny creatures definitely, other creatures probably). I think running through a rat swarm is significantly harder than running across a clean floor.

3. Concealment is another DM call, but I'd say a flying swarm would likely provide concealment to those within, and cover to those behind (since swarms are immune to many attacks, striking cover would likely just be a miss).

 

[StreamOfTheSky]

1) A Swarm is still a "creature" occupying a space. On the other hand, you can't over run it and tumble really wouldn't help...I'd treat it as difficult terrain, which normally stops a charge. I don't think you should be able to cast in a swarm without some sort of concentration check, that just seems wrong.

2) I would rule it as difficult terrain, as above.

3) I have no idea. The above poster's rulings sound fine.

 

[Vegepygmy]

1)I don't think you should be able to cast in a swarm without some sort of concentration check, that just seems wrong.

MM, page 316: "Spellcasting or concentrating on spells within the area of a swarm requires a Concentration check (DC 20 + spell level). Using skills that involve patience and concentration requires a DC 20 Concentration check."

 

[Theo R Cwithin]

Thanks for the replies. Sounds like these points are all open for DM rulings (Except the Concentration thing; I was wrong on that one. @Vegepygmy, thx for re-emphasizing the Distraction text.)

Ahnehnois's concealment/cover idea looks like a good starting point.

As for movement through a swarm, I think keying it to the relative sizes of the mover and the size of the swarming beasts is reasonable. It seems logical that a halfling would consider a rat swarm difficult terrrain, but a giant would not.