Century Worm (CR 19)

Gargantuan Vermin
Alignment: Always neutral
Initiative: -2 (Dex); Senses: tremorsense 120 ft.

AC: 29 (-4 size, -2 Dex, +25 natural), touch 4, flat-footed 29
Hit Dice: 40d8+240 (420 hp)
Fort +28, Ref +11, Will +13
Speed: 30 ft., burrow 20 ft., swim 10 ft.
Space: 20 ft. (coiled)/15 ft.
Base Attack +30; Grapple +54
Attack: Bite +38 melee
Full Attack: Bite +38 melee
Damage: Bite 4d6+18
Special Attacks/Actions: Improved grab, keening, swallow whole, wriggling progeny
Abilities: Str 35, Dex 7, Con 22, Int -, Wis 11, Cha 2
Special Qualities: Acid resistance 20, vermin traits
Feats: -
Skills: Swim +20
Advancement: 41-80 HD (Gargantuan); 81-120 HD (Colossal)
Climate/Terrain: Any land and underground
Organization: Solitary
Treasure: -

Source: Fiend Folio

Some believe that nature is a chaotic, destructive force that cares little for the concepts of morality or fair play. Such devotees of wild destruction and entropy often point to the dreaded century worm as evidence of their philosophy and single out the repulsive, voracious creature as the living embodiment of the uncaring wrath of the natural world.

A century worm is composed of seven translucent segments of pulpy flesh topped by a menacing head partially covered by a hood of rough, dark brown skin. Its round, tooth-lined mouth easily accommodates an ogre. Hundreds of squirming larvae about the size of a human's arm line the worm's stomach, which doubles as a womb. These little creatures sometimes spill out of the worm's mouth, though they die within an hour for want of their parent's life-giving nutrient bile.

Century worm larvae are far from harmless to creatures that find themselves trapped within the parent. Once the litter has sapped the life out of a victim, one larva takes up residence in the victim's body, where it gestates for a period of 100 years.