Lobstrosities are giant lobsters located in the southeast corner of the Underwater area of Fossil Island. Most weapons and shields cannot be equipped in this area. Weapons that can be equipped and used to kill lobstrosities include the trident of the seas/swamp, brine sabre, and Magic Secateurs.
A fishbowl helmet cannot be worn in this area, but players can easily use the nearby air bubbles to replenish oxygen while fighting lobstrosities.
Drops[]
100%[]
Item Quantity Rarity GE market price 
Raw lobster 1 Always 210
Runes[]
Item Quantity Rarity GE market price
Water rune 100 Common 400
Chaos rune 20 Uncommon 1,780
Nature rune 10 Uncommon 2,170
Death rune 10 Uncommon 2,030
Seeds[]
This monsters drops seeds from the allotment seed drop table.
Item Quantity Rarity GE market price
Seaweed spore 1–5 Uncommon 964–4,820
Limpwurt seed 1 Uncommon 30
Strawberry seed 1 Uncommon 5
Marrentill seed 1 Uncommon 5
Jangerberry seed 1 Uncommon 2
Tarromin seed 1 Uncommon 10
Wildblood seed 1 Uncommon 53
Watermelon seed 1 Rare 71
Harralander seed 1 Rare 31
Ranarr seed 1 Rare 45,466
Whiteberry seed 1 Rare 4
Mushroom spore 1 Rare 67
Toadflax seed 1 Rare 795
Irit seed 1 Rare 47
Belladonna seed 1 Rare 57
Poison ivy seed 1 Rare 18
Cactus seed 1 Rare 98
Avantoe seed 1 Rare 1,675
Kwuarm seed 1 Rare 379
Snapdragon seed 1 Very rare 54,551
Cadantine seed 1 Very rare 1,034
Lantadyme seed 1 Very rare 2,358
Dwarf weed seed 1 Very rare 423
Torstol seed 1 Very rare 58,385
Herbs[]
The herbs dropped vary between noted and unnoted.
Item Quantity Rarity GE market price
Grimy guam leaf 1 Common 15
Grimy marrentill 1 Common 13
Grimy tarromin 1 Common 132
Grimy harralander 1 Uncommon 674
Grimy ranarr weed 1 Uncommon 7,640
Grimy irit leaf 1 Uncommon 775
Grimy avantoe 1 Uncommon 1,814
Grimy kwuarm 1 Uncommon 1,165
Grimy cadantine 1 Uncommon 1,312
Grimy lantadyme 1 Uncommon 1,391
Grimy dwarf weed 1 Uncommon 448
Other[]
Item Quantity Rarity GE market price
Numulite 5–14 Common (9/35; 26%) 100–280
Coins 1,000 Common Not sold
Pufferfish 1 Common Not sold
Seaweed 6 (noted) Uncommon 270
Giant seaweed 6 (noted) Uncommon 2,772
Toad's legs 2 (noted) Uncommon 1,026
Caviar 2 (noted) Uncommon 480
Oyster pearls 1 Uncommon 778
Unidentified small fossil 1 Uncommon (1/70=1.4%) Not sold
Unidentified medium fossil 1 Rare (1/140=0.71%) Not sold
Unidentified large fossil 1 Rare (1/175=0.57%) Not sold
Unidentified rare fossil 1 Rare (1/700=0.14%) Not sold
Clue scroll (easy) 1 Rare Not sold
Gem drop table
In addition to the drops above, this monster has access to the gem drop table.
Show/hide gem drop table Item Quantity Rarity GE market price
Uncut sapphire 1 Rare 455
Uncut emerald 1 Rare 679
Uncut ruby 1 Rare 1,249
Nature talisman 1 Very rare 744
Uncut diamond 1 Very rare 2,627
Rune javelin 5 Very rare 875
Loop half of key 1 Very rare 10,307
Tooth half of key 1 Very rare 10,840
Rune spear 1 Very rare 11,933
Shield left half 1 Very rare 65,697
Dragon spear 1 Very rare 37,226
Trivia[]
- Lobstrosity could be a reference to The Dark Tower series by Stephen King where creatures of the same name appear in the second book, The Drawing of the Three.
- Upon release, lobstrosities only dropped a maximum of 1 seaweed spore. This was increased to 5 in an update on 12 July 2018.