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.
Herbalist in the group mistakes one plant for another and mistakenly poisons the group. Not to death, but pretty darn ill with recurring symptoms until the cause and cure are realized. (Local people may be able to help rather easily. "You ate Dragon's Rot you fool, looks and smells just like mint except it has these small thistles on the root. Only grow in the Hornwood Forest, that must be where ya got them. Eat this and you will feel better in 4 hours."