We just got back from Wilderness too. Those yellow flies were horrible. the kids kept calling them "yellow ladybugs" until they got bit and that was the end of that cute little name! They bothered my husband much more than me, but he said they hurt when they bite. The bug spray didn't keep them away. I don't think we used a very strong one, though. We went the third week of June. I don't know if they are all gone by August. Hopefully they will be.