Hollow City, Coldharbour has a major ant problem, in the form of a bot train. They spawn at the HC wayshrine, run to The Groundskeeper npc and then vanish after a bit. There's a constant stream of them and there are literally hundreds of them.
I don't know if this is related, but in the area they run through, all of the alchemy mats seem to disappear as soon as they appear. I've watched time and time again where a node spawns and then disappears after about 5 seconds or so with nobody around it. I've just witnessed it three times as I wrote this post.
I just read in chat where it's believed they run a quest for the gold, mail it off then reroll - rinse & repeat.