Whoever wrote the bestiary entries for some of the common swarm types seem to have made no attempt at realism. Ant, centipede, spider, cockroach, and many other walking insect swarms all have a speed of 20-30 ft, and I can find no restrictions on double moves or "running". Even without running this means they can move 40-60 feet per round. That is 4.5-7 mph!
Hello, an ant moving 7 mph? Real ants and centipedes struggle to break 1 mph. Morever, there is no way a swarm of 1000s of creatures crawling all over each other can move at their individual maximum speeds. 5 ft would be a generous movement speed for these types of swarms. Swarms of this kind should be pretty much static in a location and only chase the party slowly if at all.
And become non-threats entirely. Sometimes realism must take a backseat to gameplay. And in some cases, it has to hang on to the rear bumper.
Realism has no place in D&D. Verisimilitude on the other hand...
Realism has no place in D&D. Verisimilitude on the other hand...
Very fantasy and fiction are build with some degree of realism as foundation.
Swarms that you can't run away from and can't damage unless you brought enough bottles of swarm-counter (alchemist's fire) is not good gameplay. It would be much more interesting if the party was forced to deal with swarms in a realistic non-combat way such as avoiding them, baiting them away, using stealth, covering yourself in something to hide your smell, etc.
Barring a well prepared caster, lamp oil has always been our go to for swarms. By the time we come upon swarms that lamp oil can't solve, we either have a well prepared caster or someone with enough UMD to approximate one.
Also, I don't see why those non-combat solutions wouldn't work as long as you can detect them before they see you.