Maybe? I've never played past AD&D. Is that how they do it in 3.5?
Swarms are just a monster type, immune to non-magic weapons for the most part. Threatened by fire. They take up X number of 5 foot squares and are basically dispersed instead of being killed. Basically, instead of statting up a single bug, you create a "monster" composed of a lot of bugs and then play out logic required for a monster composed of a bunch of bugs. You can move through a swarm, giving it an automatic hit against, for example. Requires a Will Save to get through without giving in to the "fear"/ickiness.
I even wrote a PDF once about adapting the swarm rules for dealing with mobs/street riots and swarms of other "big creatures" like a swarm of stirges. A stirge is pretty formidable against 1st level characters but against 9th level characters, not so bad. But if they acted like a swarm, then they would be scary. I suppose for epic play you could have a swarm of dragons.... (That would work better in 3.x/4.x where Epic play (stuff way beyond name level) isn't monty haul or anathema.)