
Notes
They are one of the few creatures known to drop more than one charm at a time. They drop gold charms most often.
Charm Drop Rates 
Tactics
Wear armour that boosts your magic stats and attack using magic. Casting slayer dart is quite effective against these. You can also use the black salamander's magic style against them. If you do want to use melee, use Veracs because it hits through defence.
Examine
No one likes crabs...especially really big ones.
Top Drops
Rock-shell gloves, Rock-shell chunk, Rock-shell splinter, Rock-shell shard, Rock-shell boots, Clue scroll (level-2)
Drops
Bones (100%), Coins (27-137), Mithril hatchet, Steel platebody, Black warhammer, Black claws, Black platebody, Adamant warhammer, Adamant longsword, Earth runes (14-30), Water runes (24), Mind talisman, Fire talisman, Body talisman, Water talisman, Nature talisman, Cosmic talisman, Raw lobster, Raw bass, Casket, Grimy herbs, Tinderbox, Poison ivy seed, Gold charm (3-10), Green charm (3-10), Crimson charm (3-10), Blue charm (3-10).