"Garth Agarwen . . . The ruins of an ancient fortress of Rhudaur, now overrun by corrupted nature and a vile necromantic power out of Angmar. The most terrible power still remains to be confronted."
It may seem impossible that so small a creature can have so large an impact on the world, but it is the case that the small insects driven to madness by the caretaker of the woods of Agamaur are such creatures. Grimbark has long held control of the Arboretum at the behest of the Red-maid and with his corruption has driven all lining denizens of the swamp mad.
You are tasked with destroying Grimbark, but you should avoid harming the bees under his dominion.