The party encountered six of them in Session 68.
According to Chesty:
These large insects burst out of the ground and grabbed at our horse. They were of such size that they were able to kill and pull our horses underground in one swift action. They did not appear to be waiting in holes, but to actually have such strength and size they forces themselves up through a layer of dirt and pulled two of the horses down into the ground to the point we could almost not see any of the horse left before we could react.