How would you run a 'swarm'?

cross-posted from: https://lemmy.world/post/1312322

I've been DMing a small group of new players. They've been literally "hit or miss" with combat. I know at least one is getting frustrated with combat because he can't roll to save his life. I'm planning on throwing a swarm of small creatures at them next session. goblins, spiders, whatever. just small easily killed, easily hit creatures. Thing is I don't want to do 'initiative' per se as I'm considering having a ton of these things. Anyone have any pointers?