These spawn near where Cubert spawns and seem to be a place holder. If one is out and about, it will most likely be near entrace to Aquaducts by the bank in S Queynos. Too bad they seem to be rather rare down there. You have to kill snakes, gelataneous cubes, bats, rats and large spiders to get them to spawn. But, if you are killing time waiting for Cubert, they can make it worth your while. Drops from all give you at least a few silvers and some golds from the merchants above.