"You conjure a swarm of voracious insects to envelop your body. Enemies that strike you in battle attract their ire, and have a 50% chance of being swarmed in turn.
Enemies with this effect take 3 untyped damage initially, and an additional 3 untyped damage every 2 seconds for 6 seconds."
This is a level 4 spell, 25 SP cost, 1 minute per level duration. I think a 50% chance of 12 damage might be a little bit low for the sp cost. Maybe give it 3d4 plus 3d4 every 2 seconds for six seconds 100% chance. Something to make the spell a little bit more worthwhile.