Monstrous Scorpion, Gargantuan (CR 10)

Gargantuan Vermin
Alignment: Always Neutral
Initiative: +0; Senses: darkvision 60 ft., tremorsense 60 ft., and Spot +4

AC: 24 (-4 size, +18 natural), touch 6, flat-footed 24
Hit Dice: 20d8+60 (150 hp)
Fort +14, Ref +6, Will +6
Speed: 50 ft.
Space: 20 ft./15 ft.
Base Attack +15; Grapple +37
Attack: Claw +21 melee
Full Attack: 2 claws +21 melee and sting +16 melee
Damage: Claw 2d6+10, sting 2d6+5 and poison
Special Attacks/Actions: Improved grab, constrict 2d6+10, poison
Abilities: Str 31, Dex 10, Con 16, Int -, Wis 10, Cha 2
Special Qualities: Vermin
Skills: Climb +14, Hide -8, and Spot +4
Advancement: 21-39 HD (Large)
Climate/Terrain: Warm desert
Organization: Solitary or colony (2-5)
Treasure: None

Source: Monster Manual

Monstrous scorpions are vicious predators that make unnerving scuttling noises as they speed across dungeon floors. A monstrous scorpion has a low, flat body: 40 feet long, 20 feet wide* and 5 feet high**.
*The number includes the scorpion's body and its legs; the actual body width is about a third of the total.
**The number indicates the height of the creature's body; the creature's stinger usually is held about as high off the ground as the creature is wide.