This story was originally published in August 2019. Emerging in full force mid-summer, deer flies and horse flies are among the most intimidating creatures in the Northeast. Their bites are painful, and once they’ve home in on a target, they’re nearly impossible to shake. When pest experts talk about these types of flies, it sounds like they’re discussing monsters or aliens from a Hollywood thriller. “Their mouthparts are described as knife-like or scissor-like,” said Jim Dill, a pest management specialist for the University of Maine Cooperative Extension.