The fortress weavercrabs are physically identical to their direct ancestor. The main development is in their behavior. Rather than digging the extensive tunnel systems that their ancestor did, the weavercrabs dig small clusters of chambers which are connected to nearby clusters by single tunnels.
Also, these creatures construct walls around the entrances of their nests to keep out predators. The fortresses (pictured) from which this species gets its name can be up to ten metres tall.