Hendrickson mayfly hatch (Ephemerella subvaria) is is a major mayfly on the freestone streams throughout Northern Wisconsin. The abundant nymphs are found in the riffles among the rock and gravel bottom. Depending on the Spring weather patterns and stream conditions, the Ephemerella subvaria nymphs will be hatching anywhere from mid-April to mid-May. If the temperatures stay cooler the hatch can last for 2 to 3 weeks, offering fly fishermen some great Spring dry fly fishing.
During the morning hours trout will begin to key in on the Ephemerella subvaria nymphs. The Hendrickson nymphs become very active, and their wing cases will turn very dark before emergence. A size #12 hare's ear nymph can be deadly before the hatch. Once the hatch first begins a CDC wing emerger or a soft hackle-wet fly can take a lot of trout. When the small gray-winged sailboats start to cover the water a size #12 or #14 comparadun, or Sparkle Dun pattern can make an exciting afternoon of fishing.
The male Ephemerella subvaria duns are generally smaller than the females, including larger eyes and dark reddish body color. The classic male Hendrickson dun pattern is the Red Quill. The female Hendrickson duns (Classic Light Hendrickson pattern) are more of a gray-brown color with a touch of pink and have smaller eyes. This can be important to take notice of because at times feeding trout may become very selective for either the male or female emerging duns. Hendrickson duns have three tails.
In cooler Spring weather the Hendrickson hatch will begin around 1:00-2:00 pm and can last for a couple of hours. On overcast days the hatch may sporadically occur from late morning through the afternoon, depending on temperatures. If the weather is unseasonably cold the duns may be forced to ride on the water for a long time before being able to fly off which makes the helpless duns an easy meal for rising trout.
In the evening don't pass up the terrific Hendrickson spinner falls. They generally occur around dusk over the riffles and faster sections of the river. Hendrickson spinner falls may also appear in the morning during unusually warm Springtime temperatures. A Rusty Spinner pattern in sizes #12 or #14 is the best choice for the Hendrickson spinner falls.