The Creeping Ruin to the east is crawling with fully-grown Shadraspawn spiders. They're large enough to drag off an entire dwarf in the night, and you'll see evidence enough of that when you get there... bodies are cocooned all through the ruins.
They don't keep them alive for long, <name>, but they feed off the bodies for days. It's too late to save the victims, but we can't let those spiders grow fat and thrive. Make sure you get rid of those cocoons.