Giant rock crab

Giant rock crabs are massive versions of the weaker Rock crab. They lie in wait for prey, disguised as large boulders. When approached, they attack, unless they have become tolerant, in which case they remain as "boulders" - attempting to target them gives the message "Invalid target."

Giant Rock Crabs are good droppers of charms, as they drop 3 of them at a time. They also drop various black equipment (platebody and claws), worth a decent sum of coins. They are the only droppers of rock-shell parts, which are needed to create Rock-shell armour.

Locations

 * In Waterbirth Island Dungeon (a partner is required in order to do this).
 * In the Chaos Tunnels (The middle south rift just east of Mage of Zamorak (Abyss) leads directly to them). This is recommended when one does not have a companion.

Strategy
Giant Rock Crabs are extremely resistant to Melee and Ranged attacks, and thus are only effectively killed using Magic. However, Verac's armour and Diamond bolts (e) are quite effective with their shared unique effect, which can hit through their high physical and ranged defence, Verac's armour also has a prayer bonus allowing the player to use Protect from melee for longer than usual. This method is advised for those with a low Magic level but high melee combat levels. For lower attack levels the use of Attack Potions can be used to improve the chances of hitting. Rock Crabs drop three charms at once, and are a very good source of gold charms. These Crabs are not immune to poison, but are extremely difficult to poison them with a poisoned weapon like the dragon dagger or any poisoned ranged ammo because of their high Melee and Ranged defence.

Another method includes wearing rune or better armour, and bringing a weapon with a high crush attack bonus, such as the Zamorakian spear or Barrelchest anchor. Slash weapons such as the Abyssal whip are not recommended due to the crabs' high slash defence.

A notably effective and economic way to kill Giant Rock Crabs is the Black Salamander, or the Polypore Staff. The Black Salamander's magic attack, and the Polypore staff's attack acts as a normal magic attack and takes advantage of their lower magic defence. Their magic defence is so low you can utilise high level defensive armour without losing much accuracy.

In the Chaos Tunnels, they will eventually lose aggression. When they do, just leave the cave via the rope exit. Then just go straight back down the crevice.

Giant rock crabs have a very high defence, but relatively low attack and strength. If attacked in the Chaos Tunnels they will walk off and stop attacking you after a minute or two.

If using mage, note that they are most vulnerable to fire-based spells.

Mage Gear is as follows: Note: Another useful tactic is to use (Elite) Void knight equipment, preferably with a Deflector and a good mage robe top.
 * Helmet: Farseer helmet > Infinity > Ahrim's > Dagon'hai > Mystic/Sacred clay
 * Necklace: Stream necklace > Amulet of fury > Amulet of glory > Amulet of magic/Amulet of power
 * Cape: God cape > Soul war cape > Ardougne cloak (4/3>2) > Obsidian cape, Cape of Accomplishment,
 * Body: Ahrim's > Infinity > Dagon'hai > Mystic/Sacred clay
 * Legs: Ahrim's > Infinity > Dagon'hai > Mystic/Sacred clay
 * Weapon Slot: Polypore Staff, Elemental staff or a 'Magic damage'-increasing staff
 * Shield: God book (Unholy>Ancient>Balance) or Broodoo Shield > Mage's book > Arcane spirit shield
 * Gloves: Barrows gloves > Rune gloves > Lunar gloves > Regen bracelet
 * Boots: Infinity > Wizard's > Mystic > Lunar > Swanky
 * Ring: Seers' ring (i) > Tokkul-Zo > Beacon ring > Ring of Wealth

If you are using ice burst or barrage the arcane stream necklace is not as important here because magic damage boost adds only to the target you click on. The other 8 targets do not receive the damage boost from it or your staff, so you would be better off using a necklace with a prayer bonus.

If using burst or barrage spells the Staff of light is recommended despite the lower mage bonus (in comparison to Master wand, or Chaotic staff) given the fact that it gives free casts; when used in conjunction with Battle Robes, it has a 50% chance of saving runes when casting. Even when this effect doesn't activate, the Battle Robes themselves have a chance to save runes, effectively adding up to a 60% chance of saving runes. The Battle robes will, however, only last for 6 hours of combat after which they will need to be recharged (270 tokens).

Provided you are going to be bursting, a Tome of frost is recommended above items that provide a higher magic bonus. This is because rock lobsters have fairly low magic defence (thus the difference in offensive magic bonus is negligible), while the tome saves an inventory space and the need for Water runes.

Retreat
The Giant Rock Crab is one of few monsters in RuneScape that will retreat from battle when they become critically wounded. One way to avoid this (in the southern room in the chaos tunnels) is to kill the eastern one first (using the safespot in the picture above). Then when picking up the drop from them you will have likely alerted a few other giant rock crabs. Go back to the safespot and two should follow you there, from there kill them. While you're killing them the one you first killed should spawn but not attack (unless you go beside it). Because he spawns the other two can't get out and are trapped, so they cannot retreat. After killing the first one, don't pick up the drop and proceed to kill the second one. This means that you will not alert the one that spawned and you will have another retreat free kill. This may be repeated indefinitely in this fashion.

100%

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Runes/Talismans

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Weaponry/Armour

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Seeds

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Herbs

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Other

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Trivia

 * After the 27 May 2009 update, Giant Rock Crabs dropped Charms in groups of three instead of ten. This hidden update initially angered players, though complaints died down as the rate of charm dropping was also increased.

Giant Rock Crab Giant Rock Crab