How bad are the black flies?

[Latenighthound]

My husband and I started hiking the ADK 46 in February and are very excited for spring conditions. I keep hearing about the black flies. How bad are they really? I have mapped out several hikes through May and June. I really do not want to lose the momentum we have gained over the past few months...

If we backpack the Sewards June 4-5 will we be eaten alive???