In my world there are pixies/fairy's, little humanoids no taller than a standing squirrel, with 4 bug like wings yet intelligent as a human. Unlike traditional lore they have no magic. They do however have strong ties to nature believing that mans encroachment and devastation is an imbalance that must be corrected.
They are masters of camouflage and guerilla warfare. They fight with bows and spears tipped in deadly natural poisons. They can multiply like bunnies.
So question: As a medieval ruler tired of his peoples starving from the pixie raids killing his farmers. How can I organize the eradication of these vermin and bring an end to these tinkerbell like pests.
So I get exterminating the little guys is a tough concept given the intellectual confines of the dark ages. I will allow modern science so long as you can justify how a medieval mind could reason such a plan AND how/where they obtained the resources to enact it.
I forbid digital systems because its absurd for any single person in the dark ages to come up with ALL the advances needed to make them work. By consequence this rules out elaborate chemical reactions whose reactants would be difficult to obtain in the dark ages as well as mechanical systems requiring elaborately machined parts. Bare in mind its the dark ages not the renaissance.