These are like their giant land-based cousins in most respects. They differ in that they do not build webs per se, rather; they build underwater lairs and carefully transfer air trapped in web-sacs to the lairs. They can hide within and wait for unwary swimmers, whereupon they will scuttle out and drag their prey down, poisoning them, cocooning them, and removing them to their lair to consume.

As their lairs are air-filled, if the creature is slain, these places may be used for one hour for creatures that require air to breathe.