Many anglers that I know in Northern Michigan consider the Sulphur hatch to be the very best hatch of the year. It is a fairly long and usually very prolific hatch. It can last as long as a month in northern Michigan. Due to the usually large numbers of bugs, Sulphurs will produce some very large fish for the size of the dry fly.
There are two Sulphurs, the Ephemerella invaria and the dorothea. The first to hatch the invaria is a size 12-14 and the next bug, dorothea is a size 16-18. Don’t worry, that’s the last of the Latin!
What you really need to know about sulphurs follows. It is good to carry Sulphurs from size 12 to 18. I’m a big fan of the Robert’s Yellow Drake pattern and use it primarily for my sulphur imitation. I carry it in all four sizes. Hatch times vary by bug and weather but look for them anytime from mid afternoon until dark for the little guys. Fish can get very selective on these flies. At times you may encounter duns of one size hatching and spinners of another size falling at the same time. They can also get focused on emergers of any size. Close observation is key here.
Speaking of spinners, they are a different color than the duns. Instead of the sulphur yellow they spin having changed to a tannish to rusty color. So again you need to have three or four sizes of rusty spinners. Sulphurs will spin over riffles very late in the day, even at dark.
To effectively fish the Sulphur hatch a fly angler should have emergers, duns and spinners in at least two sizes, 14 and 18. It is better to carry them in all four sizes, 12-18 if possible. You should be on the water by 3:00 pm and stay until close to dark. You need to be very observant because this time of year is generally the most complex time of year hatch wise. In addition to all of the sulphurs there are many other mayflies that may be present.
Good luck, see you on the water.