Horseflies belong to a broad category of nuisances in the order Diptera, which also includes common house flies, deer files, and the rest of their hundred-eyed kin. But horseflies pack the biggest wallop, often drawing a wheal worthy of a hornet. Regrettably, they are found worldwide. Fun facts: Horseflies always take off in an upward direction to escape confinement. That's why commercial horsefly traps, or Manitoba traps as they are called, have their capture jar at the upper end, into which the horsefly must inevitably crawl to its well-deserved death. Also, only female horseflies bite humans.