Willow Catkin Gall
Hello. I'm a wetland scientist based in West Michigan. Attached is a photo of galls on a Salix interior that I have never seen. I shared the photo with our botanist, Bill Brodovich, and he's never seen it either. Hopefully it's not a new introduction.
Kent County Michigan
I could only find references to a mossy willow catkin gall in the UK.
I would recommend sending your picture to Dr. Howard Russell, entomologist for the MSU Diagnostic lab and ask the question. His email is appropriately, firstname.lastname@example.org. He can tell you if this is a normal occurrence here in the US. Let's hope its not a new introduction.