Cave Spider Spawner XP Farm

Cave spiders are smaller than regular spiders, small enough to fit through single-block gaps that stop nearly everything else, and they poison on hit instead of dealing plain damage. Both facts make the naturally spawning one you'll find, always inside an abandoned mineshaft wrapped in cobwebs, noticeably more dangerous to approach and trickier to seal than any other spawner type.

Clear the cobwebs and immediate area carefully rather than aggressively before building anything. Releasing a swarm all at once in a cramped mineshaft tunnel with no containment yet is a common way to take real poison damage, or worse. Approach with a shield up, and keep milk on hand to clear poison the instant it lands.

Sealing the room needs tighter tolerances than a normal spider farm. Gaps that would be fine against a full-size spider will still let a cave spider through, so every seam is worth double-checking, usually with slabs and trapdoors layered specifically to close the smaller sub-block gaps a solid block alone won't catch.

Since these spawners sit naturally encased in webbing and mineshaft scaffolding, the room around one is rarely open or regular to start with. Most of the early build time here is really demolition, reshaping the existing mineshaft into something resembling a normal sealed spawner room before you even start on funneling.

XP and string output is comparable to a regular spider farm, but honestly the real reason to build this is that you happened to find one while mining. Mineshafts with an intact spawner aren't as guaranteed as a simple dungeon, so most people don't go hunting for this one specifically.