The PCs traveling along the road/path/trail begin to hear a low droning sound. As they approach they find their path obstructed by hundred of thousands of droning insects. Locusts swarm though the air, feasting on the grass and plants. Passage will be slowed, but the insects pose no threat to the party, aside from being crunchy and disgusting underfoot, climbing into pouches and eating exposed food goods.
The Lord of the Flies, the Muscimancer has studied magics that summon, control and otherwise deal with flies. The Fly Mage is an unwholesome character, also likely to have magics of disease, rot and pestilence up his sleeves. After fighting through his swarms of flies and his loyal acolytes and slaves, the Muscimancer reveals his final power, transforming into a giant half man half fly hybrid. He can fly, acid vomit, as well as continue to use spells, wield weaponry and command his swarms.