Visit the Team Iceshanty Proshop
You can read about them at http://www.dnr.state.mn.us/volunteer/janfeb06/raw.html
I first started seeing the yellow grubs up in Minnesota in perch that were caught in shallow weeds,we would catch perch out in deep water off rock reefs that they would be clean of grubs but catch one in the weeds and they would be loaded with grubs.