It did look like some sort of willow, but I don't recall seeing a lot of them around here. The oaks, maple and birch pretty much dominate, but I suspect there are a lot of willow species in the understory that I just don't know how to ID and probably some along the wetland just to the south of our property. If the sawfly larvae eat maple and birch, they should be happy.
Any idea if they're harmful?
Thx for the help, bendy!