Thing with FB is that they are hostile to each other and to goblin invasions. They also kill anything alive on sight. So capturing FB in a room closed by a bridge ASAP, before FB dies uselessly on map, is your highest priority. Disable hauling jobs on miners. Put all stockpiles collecting from outside to "collect from linked only". Forbid all wheelbarrows and other stuff outside burrow. Enlarge burrow temporarily to dig a hole for FB ASAP.
Sometimes you can use FB, depending what material it is made of, to:
- train your marksdwarves on them (shooting from 1 level above for the dust, I guess)
- collect cheap FB silk, but still silk, in a silk farm (use chained dogs as bait and bridges to control production)
- destroy irredeemable FBs made of weaker stuff (risky business, as you can lose your precious FB, better just floor roof in the room and use a cave in on rejects, or release it during invasion)
- use FB in traps and dust-fire-poison-web shooting towers (I think you need to use 2 lines of fortifications, when the trap is set for demons passing by)
What I am getting sad over is Titans. They can learn and can be caged like regular animals. However Titans don't breed and it is a soft naked target with no economic uses for it. Intelligent species, not only hostile, but also animals are getting me so sad when they are being hunt down by my hunters. I wish I didn't have to kill them, but it is what you always have to do with uninvited immigrants/invaders.
~ Indeed, so breathtakingly sad... I wish we could catch them, retrained them, and make slave colony of these specimen. If they could haul stuff and be a meat shield for my Dwarves during invasions, I would even create for them their own shelters on my embarks and five them tools, armor and weapons, though no cloths (their degradation eats into fps). Using Trolls instead alpacas could be interesting, because of alpacas' grazing factor.