Plague Of Rats

Conjuration (Summoning)
Level Pestilence 5
Components V, S, DF
Casting Time 1 round
Range Medium (100 ft + 10 ft./level)
Effect One swarm of rats/2 levels, each of which is adjacent to at least one other swarm
Duration 1 round/level
Saving Throw None
Spell Resistance No

Black balls of fur litter the ground, rolling about as they rapidly expand, growing tails, feet, and snarling, diseased mouths.

You summon a number of rat swarms (MM 239) - one per two caster levels - to a maximum of six swarms at 12th level. The swarms must be summoned so that each one is adjacent to at least one other swarm (that is, the swarms must fill one contiguous area). You can summon the rat swarms so that they share the spaces of other creatures. Each swarm attacks any creatures occupying its space. If no living creatures are within its space, a swarm attacks or pursues the nearest creature as best it can. You have no control over its target or direction of travel.

(SpC page 157-158)