Knight Of The Lolth

(Drow of the Underdark, page 51, DnD 3.5)

[General]

You have mastered techniques of waging war when mounted on a monstrous spider (or similar vermin).

Prerequisite

Mounted Combat, Vermin Trainer, Ride 1 ranks

Benefit

When riding monstrous vermin, you do not need to make any rolls or checks to remain mounted if your mount travels across walls or ceilings (though if you take damage when on a wall or ceiling, the DC of the check to remain mounted is 10 rather than 5). When your monstrous vermin mount makes a charge attack, you can spend a standard action to grant it a bonus on the attack roll and damage roll equal to 1/2 your base attack bonus.

Normal

Riding a creature clinging to a wall or ceiling would require various checks depending on circumstances.