In my experience, any measurable rain in July brings them out in droves. If rain halts, they’ll be gone in a few weeks. There is a technique if out running them doesn’t work: (don’t wear bibs, or tight fitting jerseys) Stop. Wave your hands around to keep em off torso and keep a close eye on both legs. Wait for one to land and wait about 1 second. They can’t fly when they’re about to bite. Easy to kill them with a slap. Killed 17 of them once on GB. It’s not fun, but works.