Shockbulb (not the best name, but I think it'll do for now)
Low physical attributes, nearly nonexistent mental, Innate Spell (Ball Lightning), Corrosive Secretions, Immunity to Electricity, Dietary Requirement: Electricity.
Imagine you are a small and practically starving colony living off the life energy of local fish when someone plunks an arcology down in your territory.
"Sir, there's a swarm of jellyfish attached to the north wall."
"Don't bother me."
...A week later...
"Sir, there's thousands of them now. You can practically hear them moving around out there."
"Let me see," he says, putting an ear to the wall.
FWOOSH comes an immense amount of water as the weakened bulkhead, slowly dissolved by the enormous swarm in search of tasty wiring and conduit, finally gives way.