For the page on Giant rock crabs click here.Rellekka. They appear harmless as rocks but when a player walks by they will rise and follow you into combat.
It is also worth noting that (as with all aggressive NPCs) Rock Crabs eventually become non-aggressive, depending on how long the player has been in that location (usually 10-25 minutes). When this happens, the player will need to run south for about 10-15 seconds (near the pub, if you are on the western side of the river) and then run back.
It is seen as bad manners to attack other players crabs, as it greatly reduces the amount of experience both players can achieve in an allotted time period.