Girthworms are used by the Mud Dwarves both as steeds and pets, although no one else in the swamp sees the benefit of worm travel. Mud dwarves use a special grappling saddle (pierces its hide) on Girthworms to prevent them from slipping off the slick creature. Girthworms domesticated by the dwarves are typically hot branded by their owners.
Girthworm mouths have no teeth and their stomachs have no acid (producing digestive enzymes that only dissolve plant and fungus matter). The docile beasts rely on mucus excretion, burrowing, and swimming, to evade predators. However, it is known that a carnivorous species of Girthworm exists in the Paludial Sea, the "Bloodworm" that possesses a poisonous (DC 18, 1st round 1d6 Str, 2nd round 1d6 Str) bite (3d4 damage).
Ancestral Knowledge (Ex): All of the experiences of the parent Girthworm are transferred to offspring (including any halves created by a split) for 50 generations. Offspring of Girthworms trained as steeds have no need to be retrained.
Split (Ex): Slashing weapons split Girthworms into two identical worms, each with half of the original’s current HD and hit points (round down). A Girthworm with 1 HD or 1 hit point cannot be further split and dies if reduced to zero hit points.
Moisture Dependence (Ex): Girthworms can survive out of water indefinitely, but must have accesss to moisture frequently for drinking and skin absorption. A Girthworm can spend 1 hour per Constitution point in a dry environment before it dies of thirst (DMG Thirst).
Mucus Excretion (Ex): A Girthworm continuously excretes a Mucus that makes it nearly impossible to grapple or snare and gives it great speed over marsh and swamp terrain. Grapple attacks against Girthworms receive a -20 penalty. Non-magical ropes, nets and webs do not often work against them. The mucus excretion also reeks of a putrid odor, a smell which lingers for 1d4 days, causing a -2 penalty to all Charisma-based skills and similar checks.
Carrying Capacity: A light load for a Girthworm is 150 pounds; a medium load 151-300 pounds; and a heavy load, 301-450 pounds. A Girthworm can drag 2,250 pounds.