I haven't seen so many horse-flies in Normandy before this summer. Friends report being bitten by them.
They are fast, bite without warning and very-very painfully. Be aware and swat before they get you.
This is an excerpt from Wikipedia on horse-flies:
Horsefly bites are painful, the bites of large specimens especially so. Most short tongued (short proboscid) species of horse flies use their knife-like mandibles to rip and/or slice flesh apart. Flies with longer proboscides bite more like a mosquito, their stylet-like mouthparts piercing the host's skin like needles.The horse fly's bite is more immediately painful than its mosquito counterparts', although it still aims to escape before its victim responds. Moreover, the pain of a horse fly bite may mean that the victim is more concerned with assessing the wound, and not swatting the interloper. In any case defense is difficult, considering the agile nature of the fly. However, inhabitants of regions where the flies are a pest usually learn to swat immediately at the first hint of the bite, while still jumping. That usually gets the fly, especially if its escape is hampered by its having bitten through clothing. The bites may become itchy, sometimes causing a large swelling afterward if not treated quickly.