...and I'm going to fucking give it to them. (Note: This submission is largely so I don't forget the details of this plan once I'm less pissed off.)
I can explain! Really! (Note: This is for my Demon Hunting Campaign set in 1640's Ireland, so here be campaign specific dragons.)
My take on Dracula for my 1640's Demon Hunting Game
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.