Casting Time 1 round Components V, S, M/DF (a square of red cloth)
Range close (25 ft. + 5 ft./2 levels) Effect one swarm of poisonous frogs (see below) Duration concentration + 2 rounds Saving Throw none; Spell Resistance no
You summon a swarm of poisonous frogs, which attacks all other creatures within its area. You may summon the swarm so that it shares the area of other creatures. If no living creatures are within its area, the swarm attacks or pursues the nearest creature as best it can. The caster has no control over its target or direction of travel.
And here is a complete stat block for a poisonous frog swarm:
Bite—injury; save Fortitude DC 13; frequency 1/round for 6 rounds; effect 1d4 Con damage; cure 1 save.
The save DC is Constitution-based and includes a +2 racial bonus.
*Special Notes on the Stat Block: If this were truly an "animal" instead of vermin (as centipede would be) there would be many other changes to make as well. However, the spell simply says to use the centipede swarm with the following changes..." so only the changes indicated in the spell have been applied.