Anti-Vermin Barrier

With this spell, the caster creates an invisible force field that repels nonmagical insects, rodents, spiders, snakes, worms, and similar vermin of less than 1 Hit Die. The spell has no effect on giant-sized versions of these creatures unless they are less than 1 Hit Die. The barrier affects summoned creatures, such as those called by a Summon Insects spell.
Any vermin within the area of effect when the spell is cast are not affected; however, when these creatures exit the area, they cannot return.
The spell affects a cubic area whose sides are 10 feet times the caster's level (for instance, a 2nd-level priest could affect a 20' x 20' x 20' cube.

[Tome of Magic]

Sphere: Wards
(Abjuration)
Level: 1

Range: 30 yards
Components: V, S, M
Duration: 1 hour/ level
Casting Time: 1
Area of Effect: 10-foot cube/level
Saving Throw: None

Material Components:
the caster's holy symbol and a rodent's whisker