Blizzard has certain place holders that spawn in some places. Like the Stinging Winds in Act2, as far as I know two things can spawn at each end of the map. Sometimes it's that ship for the Black Rock Ledger, sometimes its a bunch of Cultist that say "HE/SHE found the camp!!! Kill them!!". Sometimes it's a big rock that appears to have a nest for those wasp on it. But nothing happens. I guess Blizzard put them there to make the random parts more random.