[RPG] Should I replace the swarm with the individual creature after enough damage


So one thing I found odd in the DM's Basic Rules v0.1pdf was a large list of animals that seemed so insignificant as to wonder why it was included in the PDF. For example, the "Rat" monster, has 1 hitpoint, and a CR of 0, it can hit for only 1 point of damage with a +0 to hit.

However, I then noticed that there are swarm creatures, such as a "Swarm of Rats" which has 24 hit points, +2 to hit, 7 damage or 3 damage when it has less than half it's hitpoints, and is listed as "Medium swarm of Tiny beasts". Swarms also have the following trait:

The swarm can’t regain hit points or gain temporary hit points.

This made me think that this was very neat. A swarm is made up of indidvual creatures, and each hitpoint means each creature died. So for a swarm of rats, I might think this means that there are 24 rats in the swarm.

But is this actually the case? When a swarm is reduced to 1 or 2 hitpoints, should I switch those out for actual rat creatures? (This would basically cause the swarm to lose the damage resistances, immunities and reduce the amount of damage it can do.)

Best Answer

You can, but there is little sense to do it.

There is not a rule about that, and, while the DM can do as he considers opportune, the individual creatures are often too weak to fight individually, and are no challenge at all for the PCs. Also, the Monster manual (p. 337) says the following about swarms:

The swarms ... aren't ordinary or benign assemblies of little creatures. They form as a result of some sinister or unwholesome influence.... Even druids can't charm these swarms, and their aggressiveness is borderline unnatural.

So it is plausible that reducing a swarm hit points to 0 does not necessarily mean killing every one of them (unless you use a fireball or similar method). Most often it means that you killed enough of them to to make the rest of the creatures in the swarm return to their standard behaviour and flee in all directions.