Cimbex Americana americana
Leaf miner of Alnus alnobetula
Leaf miner in Betula neoalaskana
Host: Betula neoalaskana
Maybe?
These are absolutely everywhere, on almost every leaf of every birch tree
About 1.5” long. Black “antennae” on its head and black tassel(s) on its rear. On what looks like Salmonberry.