People go to National Parks for many different reasons. They go for adventure. They go to wonder at the natural world. They go to learn a little bit about the story of America. Sometimes people go because they just don’t know any better. In the summer of 2005, Tyler Karp and I were working at Cuyuna Scout Camp in northern Minnesota trying to develop an off-site adventure program based at our camp. As part of our planning, we were scouting a variety of canoeing and hiking routes within a couple hours of the camp. A couple weeks into the camp season, we decided to take a two-day 50-mile hike of a portion of the North Country National Scenic Trail where it passes through the Chippewa National Forest. We had a set of trail notes and a moderately detailed map of the trail. We quickly packed water, a tent, stove, food, and other hiking essentials, yet we neglected to plan on encountering two particular foes as we set out in mid-July. In the woods of northern Minnesota are two especially pernicious pests. Many people initially think about mosquitoes, and they certainly can be a bother when they are swarming on a calm, muggy evening. However, the two insects most likely to threaten one’s sanity on a hike through the northern Minnesota woods are the horse fly and its relative, the deer fly.