The Deep and the Dark
Called ashniisku (spider + fine mount) by the dwarves of Ina-Sihirtu, and ridden by some of their most feared warriors.
- from the Monstrous Manual:
The steeder is a giant hunting spider with tarantula markings, 4+4 Hit Dice, and a movement rate of 12. It does not spin webs and cannot move in them, but its feet exude a sticky substance which allows it to cling to precarious surfaces, even if only one foot is touching the surface. The steeder also uses the secretions (50% of the time) to cling to prey; this requires an attack roll from the steeder, against AC 10 for the victim, adjusted only for magic and Dexterity. A victim can escape by making a successful Strength or Dexterity roll with a -10 penalty. While held, the victim suffers a -2 penalty to attack and damage rolls and is automatically bitten once per round.
Duergar dwarves use steeders as mounts, fitting the spiders with complex saddles and control straps. A steeder can leap 240 feet, even with a rider. Leaps are considered charging attacks. A steeder moves on walls and ceilings at half its normal rate; duergar saddles are built for this kind of motion.