I was actually going to ask that question too! We got mountain bikes last fall and have found some really out back dirt roads to ride on, but the deerflies make us miserable. I don't think bug spray is meant to work on those. Maybe one of those sound emitting devices you wear on your belt? I'm ready to try any gimmick. Someone told me you have to ride 10mph or more to get them to stay off you. But they will still follow you and get you on the hills! My husband had a swarm behind him and he said I did too. I'm sure it probably even looked like a comic strip, like us with all our flies like the pigpen character from Charlie Brown is with dirt!