Meet the horseflies of the genus Hybomitra—powerful, aggressive aerial acrobats and the ultimate test of endurance for any outdoor adventurer. Only the females bite, requiring a rich blood meal to secure the proteins needed to develop their eggs, while the completely harmless males feed strictly on flower nectar. Rather than stinging, females use microscopic, saw-like mouthparts to slice open skin, injecting an anticoagulant saliva that causes blood to pool so they can easily lap it up. Yet, despite their ruthless habits, their eyes are absolute masterpieces of nature: massive, shimmering globes of brilliant green and purple, marked by striking horizontal bands of color. Driven by sight and heavily attracted to movement, dark colors, and carbon dioxide, these flies are among the fastest insects on Earth—males of the related Hybomitra hinei can reach mind-boggling speeds of up to 145 km/h (90 mph) to chase down mates. While cycling through northern Sweden on sunny days, swarms of these relentless interceptors constantly surrounded me; I only escaped their jaws by wearing long sleeves and slathering exposed skin in thick sunscreen. On a few occasions, when a particularly bold fly landed on me, I managed to briefly knock it out. Stopping my bike, I used the few moments it took for the fly to recover to capture some jaw-dropping macro shots of their astonishing eyes. I made sure not to kill them, though I must admit, horseflies are among the very few organisms on Earth I wouldn’t mind euthanizing!