A surge of biting black flies is sweeping across the San Gabriel Valley foothills — and officials warn the infestation could get worse. Activity is currently high, with biting expected to continue for the next several weeks, according to the San Gabriel Valley Mosquito and Vector Control District. The sudden spike is fueled by warm weather and strong water flows, creating ideal conditions for black fly breeding. Often mistaken for mosquitoes, black flies travel in large numbers and can cover