Ohgod, was just attacked by a Giant Cave Spider Queen. None of my legendary marksdwarves using master-freakin-work bolts could even scratch the thing, I had to dogpile her with hammerdwarves.
The end result? One permanent invalid affectionately called "Lefty" and another now-marksdwarf known to his friends as "Dimbeard". And when I say lefty, I mean really. His entire right side is just... gone! The only thing that kept it from being a massacre was they spread out right before she sprayed them, so 4 of the 20 stayed unwebbed. But seriously, I had upwards of 30 multi-legendary dwarves fighting the thing and it was close. If she had stunned all of them, she kills fast enough that there could easily have been 8 or 9 casualties before the marksdwarves killed her or they got unstunned.
Also, I take back the part about lefty. His new name is "Torso boy". That really sucks.
Strike that again. He bled to death.
Edit: A cat walked over the webs I had carefully put restricted zones over. He got butchered by the trap under it. So now I'm out both some extremely valuable cloth and a cat. Freaking GCSQ!