So. I caught a couple of giant cave spiders in cage traps. Fuckin' sweet. I couldn't wait to play with these dudes.
I put them in a cage which I would pop open to greet invading armies, which was quite a bit of fun, although their longevity in those encounters was limited. It was also sometimes a hassle to recapture them when they did survive. When their numbers dwindled to 2, I decided to set up a little shop to make giant cave spider silk, so all my dwarves could have super fancy clothes.
I wasn't real clear on the details of how to set this type of farm up, although I knew the general idea. I decided to train one of the spiders and have it friendly, and leave the other one as an enemy, in case it turned out to be useful to have it shooting webs at one of my fortress dwarves. It went okay. I had a moment of very bad fright when I was flipping through the fortress and suddenly realized there was a giant cave spider walking down the dorm area's fucking hallway like he belonged there. Once I recovered a bit, I learned that it was the tame one, and I watched him all the way through as he navigated purposefully through my fortress, not causing a single problem or upsetting even a single dwarf, and arrived at the animal training area, which I guess had been his destination. What the fuck man. You gotta tell me if you're going to do stuff like that. His trainer arrived shortly after and they got to work, calm as a millpond.
Anyway, after quite a few failed experiments, I set up what was going to be the spider silk generation area: There was a little platform for the spider to be on, and then an 8-foot chasm, and then on the other side of the chasm was going to go a goblin. Behind the goblin were some fortifications through which the silk could shoot, and on the other side of that was the silk collection room. Flawless.
I selected a captured goblin, took his clothes and weapons away, and placed him naked on the goblin platform. I selected a goblin priest, assuming that this would give me a pretty wimpy goblin for this purpose, and he'd be a terrified spiderweb recipient and it would all go smoothly.
I don't know what kind of things go on in goblin seminaries, but apparently they're pretty hardcore. Everything went smoothly until I released the naked goblin, at which point he leapt across the chasm, grabbed onto the spider and started wildly assaulting him with bare hands and teeth, they fell together down into the chasm, and then the goblin killed the spider. What the fuck. Then the goblin died of his injuries, both of their corpses resting together at the bottom of the trench. Like lovers at Pompeii.
Welp. That was the end of the giant cave spiders. I actually never did anything else with the room, since it had no conceivable other purpose, and so the two corpses are still down there. I hope they reconciled in the afterlife and figured out that I had been the real enemy. Anyway, I set up a massive room down in the cavern-adjacent part of the fortress, managed to entice some normal-sized spiders into it, and did the whole runaround required to keep the cats out of there and harvest some regular spider silk from it from time to time, until I finally said you know what, fuck this, my dwarves can wear pigtail cloth; it is fine.