SRD:Centipede Swarm

Combat
A centipede swarm seeks to surround and attack any living prey it encounters. A swarm deals 2d6 points of damage to any creature whose space it occupies at the end of its move.

Distraction (Ex): Any living creature that begins its turn with a centipede swarm in its space must succeed on a DC 13 Fortitude save or be nauseated for 1 round. The save DC is Constitution-based.

Poison (Ex): Injury, Fortitude DC 13, initial and secondary damage 1d4 Dex. The save DC is Constitution-based.

Skills: A centipede swarm has a +4 racial bonus on Spot checks and a +8 racial bonus on Climb checks, and uses its Dexterity modifier instead of its Strength modifier for Climb checks. A centipede swarm has a +8 racial bonus on Climb checks and can always choose to take 10 on a Climb check, even if rushed or threatened.

See Wikipedia Entry: Centipede