May is the month spring aquatic insect hatches begin on local rivers and lakes.

Daytime temperatures finally climb out of the 40s and 50s, for the most part, to hover in the mid-60s with occasional daytime spikes into temperatures that suggest summer will eventually come even to northwest Wyoming.

What hatches might those be you ask? Currently, the Mother’s Day caddis are very active on the Shoshone River below Buffalo Bill Dam. These insects are size 14 or 16 and imitate small moths. Their wings are tent-shaped over their backs and are a mottled gray and black. Their abdomens are a muddied olive color on the males, while the females show a chartreuse cluster of eggs at the back of the abdomen.

After a steady diet of midges and blue-winged olives since early January, the arrival of caddis appear every year near Mother’s Day, hence the name. These insects are also called black caddis and the hatch times vary and depend on water temperatures to hit 50 degrees.

Because this is the first big hatch of spring for the trout, and because caddis are tasty to trout, the response to imitations of this insect has been well-received by the trout in the lower Shoshone the past few days. Expect the hatch to continue for a couple of weeks before the yellow Epeorus mayfly hatches later in May.

Black caddis imitations that are effective before, during and after the hatch are soft hackle wet flies. Gray partridge soft hackles with a peacock body represent the emergent phase almost perfectly. These wet flies also work during the adult phase of the hatch because the females will not only lay their eggs on the surface, but they will also dive below the surface to lay eggs near the bottom before rising to the surface. Dry flies also work well when the adults are swarming over the surface of the river. Black elk hair caddis and the Hemingway caddis are both great flies to use when you see trout slurping and gulping clusters of these insects in the top of the water column.

These dark winged and bodied caddis are also present on the lower Greybull and Wood rivers near Meeteetse and the Bighorn River near the town of Greybull. The lower Clarks Fork of the Yellowstone, Shell Creek and Ten Sleep Creek also have a caddis hatch that are going on, or will occur at any time now. Mother’s Day caddis are also very active on the lower Stillwater, Boulder, Gallatin, Madison and Yellowstone Rivers in Montana should you want to “chase” this hatch for a while. Grab your fly rods, waders and boots and see how much fun fishing different trout rivers or streams can be.

In a few weeks, if not sooner, the speckled dun mayfly called Callibaetis will be appearing on local lakes. These mayflies can be quite large in early spring. Size 12 and 14 tan sparkle duns, tan Klinkhammers, hare’s ear parachute Adams and tan X Caddis patterns work well for the adults that rise to the surface at West Lake (Kanye’s lake), East and West Newton, Hogan, Luce and other stillwater impoundments throughout the Big Horn Basin.

Subsequent hatches throughout the summer months will require the angler to drop down in size to 16 and even size 18 in order to fool the fish. Nymph, or wet imitations, to use when Callibaetis appear on the lakes would be the tan North Fork Special, beaded or non-bead head hare’s ears and pheasant tails fished with short, quick strips under the surface will bring solid strikes by trout. These wet and dry fly recommendations will even work well in lakes stocked with crappie, bluegill, bass and perch.

Last to happen in the month of May is the opening of Yellowstone Park’s annual fishing season which begins on the Saturday of Memorial Day weekend. Stay tuned for recommended flies for the Madison, Firehole, Gibbon and other rivers or streams that fish well in late May on the opening weekend.

It should be said that not all waters will open to angling to protect spawning native Yellowstone cutthroat trout. It is recommended that anglers obtain and read the new Yellowstone fishing regulations. These should be available locally by mid-May. License prices have gone up, too, so be ready to pay more for the privilege of fishing in the Park.

Not all rivers and streams will be clear and fishable either. Many in the northern part of the Park will have been impacted by the heavy flows when the snows begin to leave the mountains. Make sure you possess a current 2021 Yellowstone National Park fishing license before heading off to experience the trout fishing in the Park.

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