So I was first going to say Carrion Crawler for favorite Vermin, but then I did a little research and found that the carrion crawler is in fact an Aberration, not Vermin. Huh. Well, in that case its gotta be the Centipede Swarm!
Everyone's seen that part of Indiana Jones and the Temple of Doom where Indy and Willie (Kate Capshaw) are exploring the bug-filled tombs under Bangkok Palace, and that big centipede crawls up over Willie's shoulder and into her hair, which she doesn't notice.
What happened to that centipede? Did she ever find it? Maybe not,
maybe its still there, clutching her scalp and laying eggs or whatever in her hair, until one
day they all hatch at the same time and big centipedes just swarm out of
Yeah, so, centipede swarms are super-gross and the perfect vermin to get players to squirm. Not only do they do a little damage every round, they often have some sort of poison as part of their attack. The best kind of poison for swarms of disgusting centipedes is the kind that just slows you down, so paralysis sets in slowly, so every round you move slower and slower, get more and more bites, until the whole swarm covers you completely.
Ugh. Yeah, centipede swarms man, yuck.