Black fly and mosquito peak season upper peninsula
I expect the black fly season to extend through June for sure. You should also be prepared for an extremely heavy ceratopogonid (no-see-ums) season too, especially in places which border swampy areas. Of course whether or not it will reach nuisance levels for you will depend on where you're staying and what you are planning on doing. I expect that there will be several black fly species out in force at that time, but if I were pressed to pick one that will distinguish itself among the crowd it would be Simulium vittatum (which is generally regarded as a species complex). It's multivoltine so its numbers can grow through the season as long as it's wet, which it appears to be...very, very wet. As long as the rains continue, expect banner number of mosquitoes too.
Good luck up there,
It’s certainly very wet this spring. What are your predictions for one month from now?
Somewhere between horrible and unbelievably horrible.