Embarked on a flat (with stream) site in... whatever that high-temp sand desert worldgen is called, I forget the default name.
So far (two years), literally every surface creature that's passed through my fort has been a forest spider. This isn't too problematic in itself, except they sometimes enrage I've lost some civs every other season as a result. Surprisingly, the military dwarf that I brought along at embark does pretty well at killing them despite their web shooting. I guess they web him, target his head (protected by a helmet), and then he eventually breaks free of the web and bashes them to death in between further webbings.
I'm debating capturing some and war training them but that would probably just make a huge mess of webs everywhere. Already I want to clean up my surface of all the webs that have already been shot around intermittently, which hasn't been very successful since usually what ends up happening is another batch of spiders appear during clean up and end up shooting more webs all over the place as I send the military guy to save the civs.
It would be nice if webs eventually just decayed on their own into thread... maybe even make it moddable the time it takes (so things like GCS webs might potentially last forever, but other smaller/"less dangerous" spiders might only last a few weeks), and also the likelyhood that any decayed given web would create a thread (so it would still be profitable to harvest actual webs). I don't expect that to be added in MDF (I doubt it's even possible, although maybe a periodic dfhack script could do it, just as it fixes bugs periodically), but I'll probably pop over to the vanilla suggestion forum.
In the interim I'll probably just cheat and remove their ability to shoot webs. Maybe add it back later on when I have an army of airmancers to assign them to.