One of the most prolific Wisconsin mayfly hatches is Ephemerella subvaria, also known as the Hendrickson mayfly hatch. These mayflies are very common on the northern Wisconsin freestone streams. They generally hatch sometime in late April to early May. I have personally witnessed the hatch as early as April 8th and the Hendrickson spinners at dusk into mid-May. For the Hendrickson hatch you definitely need to tie several different patterns and carry a good supply for when you hit the hatch in full swing.
Hook: TMC 100 #12 & #14
Thread: Uni-thread 8/0 Rust Brown
Tail: Coq De Leon tail fibers
Body: Nature's Spirit #25 Pink Cahill
Wing: Fine deer hair (comparadun style) with grey Whiting dryfly hackle behind deer hair
Split the tail barbs and don't make the body too bulky.
For the dun I like to add 2 wraps of good dry fly hackle right behind the deer hair wing.
Clip the hackle underneath the body so the fly lays flush on the water.
For one type of my Hendrickson nymph patterns I use a Hends BL120 barbless jig hook to get the fly down to the bottom fast. I also tie some Hendrickson nymph patterns on light wire hooks (no bead) to fish near the surface during emergence. The Hendrickson nymphs on my favorite Wisconsin trout streams are a darker rust color and sort of stout. Tying on legs and a separate wing case I do not feel is needed. These nymphs are tumbling along the bottom and I find the trout are looking for something in the right size, shape and color.
Hook: Hends Barbless BL120 Jig Hook, Size #14 & #12
Head: Competitive Angler's 3.0mm Slotted Copper Tungsten Bead
Thread: Dark Brown thread of your choice
Tail: Grouse hackle
Ribbing: Copper Wire
Body: Australian Possum dyed rust color
Thorax: Australian Possum dyed dark rust or black color
My 2 favorite Hendrickson emerger patterns are shown below....
Hook: TMC 2487 size #12 & #14
Thread: Veevus brown or Uni-thread 8/0 Burnt Orange
Tail: Brown Zelon fibers (sparse)
Rib: Fine copper wire
Abdomen: Awesome Possum Rusty Brown
Thorax: Nature's Spirit #25 Pink Cahill
Hackle: Grey Dun rooster hackle (2-3 wraps over top of thjorax)
Wing: Grey CDC feather over top of thorax and dun hackle
Hook: Hends BL254 size #12
Thread: Veevus or Uni-thread 8/0 Burnt Orange
Tail: Grouse fibers
Rib: Live4FlyFishing UV Ribbing no. #12
Body: Dyed rusty orange Australian possum dubbing
Wing: dyed grey hen feather
Tie the hen feather in first pointing forward. Tie in the tail, ribbing and dubbing. Place the thread at the back of the thorax section and wrap the hen hackle towards the back of the hook shank stopping when you reach the thread. Secure the feather tip with two thread wraps and snip off the tip of the feather. Wrap the thread forward through the hackle wraps up to the eye of the hook then whip finish the fly.
I prefer a simple nymph pattern that is super easy to tie and extremely effective cast across and down. It is just a tail and a symmetrical body tied in the right hook size (Mustad 3906 hook, size #12) and colors. I wrap copper wire around 2/3 of the hook shank after I secure the thread onto the hook.
Then I tie in a few darker colored grouse fibers for the tail. After that I dub in some dark rusty brown Awesome Possum dubbing about 1/3rd of the way forward. Lastly I add some black Awesome Possum dubbing mixed with some dark rusty brown Awesome Possum dubbing.I wrap it tightly all the way to the eye of the hook and whip finish. That is it. I don't even bother tying in any legs and the trout don't seem to mind.
If you ever look closely at the real nymphs in the northern Wisconsin freestone streams you will notice they have a darkish rusty brown abdomen and a blackish wing case when they are ready to hatch. Also, the nymphs are fairly stout so I prefer tying the Hendrickson nymphs with dubbing rather than pheasant tail fibers to add more bulk. It is really about the silhouette, shape and color. Keeping the dubbing tightly wrapped also helps the fly sink faster.