Do come prepared to protect yourself. Large numbers of black flies are usually gone by July. Some years, the island has relatively few. In a heavy year, they may not be completely gone until frost. Fortunately unlike mosquitoes, black flies do sleep at night.
Mosquitoes mostly hatch in standing water during warm weather.
In a typical year they get off to a quick start and then slowly taper down as the summer dries out. In a rainy summer, they will stay at high numbers. At least some mosquitoes will hang on until a heavy frost finally ends their season. Deer flies and horse flies are most prevalent during the warmer months. Stable flies can be quite numerous during periodic hatches, mostly along shorelines.