Level: Drd 7
Components: V, S
Casting Time: 1 round
Range: Close (25 ft. + 5 ft./2 levels)/ 100 ft.; see text
Effect: One swarm of centipedes per two levels
Duration: 1 min./level
Saving Throw: None
Spell Resistance: No
When you utter the spell of creeping doom, you call forth a mass of centipede swarms (one per two caster levels, to a maximum of ten swarms at 20th level), which need not appear adjacent to one another. You may summon the centipede swarms so that they share the area of other creatures. The swarms remain stationary, attacking any creatures in their area, unless you command the creeping doom to move (a standard action). As a standard action, you can command any number of the swarms to move toward any prey within 100 feet of you. You cannot command any swarm to move more than 100 feet away from you, and if you move more than 100 feet from any swarm, that swarm remains stationary, attacking any creatures in its area (but it can be commanded again if you move within 100 feet) . . . (Wizards of the Coast, 3.5 SRD, Spells C).
“. . . Swarms are dense masses of Fine, Diminutive, or Tiny creatures that would not be particularly dangerous in small groups, but can be terrible foes when gathered in sufficient numbers. For game purposes a swarm is defined as a single creature with a space of 10 feet—gigantic hordes are actually composed of dozens of swarms in close proximity. A swarm has a single pool of Hit Dice and hit points, a single initiative modifier, a single speed, and a single Armor Class. It makes saving throws as a single creature.
Many different creatures can mass as swarms; bat swarms, centipede swarms, hellwasp swarms, locust swarms, rat swarms, and spider swarms are described here. The swarm’s type varies with the nature of the component creature (most are animals or vermin), but all swarms have the swarm subtype.
A swarm of Tiny creatures consists of 300 nonflying creatures or 1,000 flying creatures. A swarm of Diminutive creatures consists of 1,500 nonflying creatures or 5,000 flying creatures. A swarm of Fine creatures consists of 10,000 creatures, whether they are flying or not. Swarms of nonflying creatures include many more creatures than could normally fit in a 10-foot square based on their normal space, because creatures in a swarm are packed tightly together and generally crawl over each other and their prey when moving or attacking. Larger swarms are represented by multiples of single swarms. A large swarm is completely shapeable, though it usually remains contiguous . . .” (Wizards of the Coast, 3.5 SRD, Monsters S)