It seems Giant Cave Spiders don't notice cats or kittens. These three GCS are wild, untamed, 2 males and a female, and all three have killed enough dogs, elk, and horses to have titles. I don't have the Dungeon Master, anyway. Anyway, these three cats have been roaming the pits, cuddling with the spiders, and generally GALLIVANTING since they were thrown in here as kittens. I figured this was a Toady easter egg, that adorable kittens are ignored by the underground's most feared natural beast
however, upon growing up, they are still immune to the wrath of my spider guests. Maybe this is intentional so that the Fun and challenge of lurking GCS aren't immediately ruined by cat exploration in every fortress?
In either case, now I have a spider pit filled with spiders and cats, both populations are capable of breeding (modded wild GCS reproduction in) and it would take some doing to get back in and clean them out. :| Those kittens were extras meant to be eaten, HALP!
*Update: Removing the [VERMINHUNTER] tag from the cat's entry in creature_domestic.rar and then reloading my save INSTANTLY caused the GCS to slay the cats. This is likely caused by the [AMBUSHPREDATOR] tag on the GCS as he's the only unit that has it, and this is likely as I said earlier to prevent cats from "triggering" the spider ambushes rather than dwarves.