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3. Midwest Lata Emergence

(refers to lata itself)

(Note: Caucci & Nastasi write a bit about how lata is a midwestern species only, and cornuta and others account for the eastern reports. So I can take these notes to refer to its midwestern behavior.)

Lata is a first-rate hatch int he midwest. General emergence in MN, WI, and MI is from the end of June to mid-August. Best hatching on northern rivers, like Michigan's Au Sable and Wisconsin's Wolf, is from mid-July through the first week in August.

Unlike the more feeble-legged Ephemerella nymphs, these flattened nymphs live in faster stretches, especially those with gravel bottoms. The emergence characteristics of these nymphs are typical of the entire genus. They wiggle enticingly to the surface, often making several attempts to break through the surface tension. In the Drunella subgenus, they have a tendency to hatch 6 to 12 inches below the surface and float to the top, buoyed by gases previously released by the nymph.

In early July, before the hatch is in full swing, emergence may occur in the afternoon, especially on cloudy days. During this period, there is little other activity during the day, so trout may feed on the sparse emergence of duns if they float by convenient lies.

In mid-July when the water gets warmer, good hatching normally takes place in the mornign whent he water is still cool. During this time, emergence can occur anytime between 5am and noon, but the best hatching and feeding activity will usaully take place between 7 and 10am.

Lata duns are sporadic emergers which usually hatch over a four-hour period.

The best time for these ideal fly-fishing sessions is generally the 3rd and 4th weeks of July.

Due to their frequent subsurface emergence, the hatched lata duns normally float complacently, drying their wet wings before takeoff. This characteristic, and the fact that htey are often funneled into pools and backwaters having smooth surfaces, makes them ideal for the Compara-dun application.

The spinner flights are both impressive and productive. About an hour before dusk, the male spinners will usually appear over the riffles. On Midwestern waters, these spinner-falls usually precipitate some of the best feeding activity of the year. The spinner-fall and subsequent feeding activity will last about an hour; usually between twilight and dark.

A riffle with good trout-holding capacity and one that also has good lighting conditions (preferably to the angler's rear) is of primary importance. If the trout seem to be slashing at the ovipositing imagoes we often start out with full-hackled spinner patterns and manipulate them to imitate the dipping spinners.

(refers to syn. cornuata)

Cornuta hatching takes place on northern and westenr PA streams between mid-May and early June, but the best activity occurs between May 25 and June 3. Catskill emergence lags by a week or two. We photographed Beaverkill specimens on June 15th while we camped at Wagon-Tracks pool.

Northern streams, like those in the Adirondacks and northern New England, continue hatching throughout June. General emergence in the Midwest is from late May to the beginning of July, while emergence in northern MN, WI, and the uP of MI usaully continues until the second week in July.

Although cornuta nymphs are found in slower waters, their flattened profile, which is typical of the Drunella subgenus, extends their habitat to runs and riffles and eddies of pocket-water.

Cornuta nymphs live in medium-to-fast riffles having gravel, pebble, or medium-sized rock bottoms. During emergence the may migrate to slower sections and eddies. As do most Ephemerella nymphs, they make several trips to the surface during emergence.

The nymphs, in most cases, seem to split their shucks several inches below the film or right in or beneath the film. The trout key in on the emerging nymphs or freshly emerged duns.

Unlike most Ephemerella species, the body of the dun changes its color drastically once it hits the atmosphere. As the duns hatch in or beneath the surface film, their body is a pale greenishyellow color (almost chartreuse). Within seconds after emergence (when the duns are floating on the sruface) the bodies turn a medium olive. By the time they fly to the nearest shrubbery, they are a dark dirty olive.

They emerge in the morning, at a time when the peak of other mayfly activity occurs during the evening hours and at dusk.

Finally, we believe that cornuta's obscurity was due to a simple case of mistaken identity. We are convinced that even the most serious experts have mistaken the activity of cornuta for that of Ephemerella attenuata.

Our experience with cornuta indicates that they ill hatch anytime between 8am and midday, that emergence usually lasts from 60 to 90 minutes and that the best hatching activity takes place when water temp is between 50 and 60F.

The cornuta duns hatch in riffles and medium-to-fast runs as well as in eddies and back-waters adjacent to these areas. AFter emergence, they ride the current momentarily before they become airborne.

The most effective imitation for this hatch is a sparsley tied deerhair compara-emerger with a greenish yellow body (almost a chartreuse) fished in the surface film.

The glassy-winged imagoes are still somewhat of a mystery to us although we have sighted them many times over the riffles about an hour before dusk. Thus far we have found their significance questionable, as most spinners seem to drop their eggs a safe distance above the stream.

(described for cornuta)

They emerge during midsummer mornings in eastern and midwestern streams.

The nymphs of E. cornuta and those of their closely related species inhabit medium- to fast-running portions of streams. They may also be found in the sluggish margins of deep pools, clinging to dthe debris and organit detritus that collect in them.

Daily emergence of E. cornuta and all species that follow is from nine in the morning until noon. As a general rule, spinner falls of these species appear to be of limited importance to anglers with the exception of E. lata, an extremely common midwestern species that emergers during July and August.

Their large size and early seasonal occurrence in June serve to separate them from E. cornutella, which is almost morphologically identical though noticeably smaller, and which follows it in emergence.

(described for longicornis)

Good populations of E. longicornis are found in the trout streams of North Carolina and Tennessee, and the species is capable of causing fair BWO hatches for the Smoky Mountain angler. Its seasonal emergence takes place from the early part of June until the end of July, with daily appearances between ten and one o'clock in the afternoon.

(described for cornutella)

SEasonal emergence takes place from late June through August, with daily occurrences during the morning from 9am to 11am. The best hatches are in moderate-flowing streams common throughout the Allegheny mountain ranges.

(actually described as lata)

Some rivers in the East, such as the Beaverkill and Saranac, support fair to good populations. Morning hatches can be expected to occur from late June until the end of August. Immense spinner swarms gather at dusk. The spinner falls are very impressive, and usually entice the frenzied feeding of trout.

They usually exhibit bright, crimson dashes on their legs, thorax, and abdomen; however, the species is known to have distinctive and different color phases.

Habitat: Nymphs occur widely in gravel riffles in steams of all sizes

Emergence: June 25-August 13

The evening hatches stimulate trout feeding activity for several weeks after the majority of our mayflies have completed their adult life.

(about cornuta)

Habitat: Nymphs inhabit gravel- and stony-bottomed streams in moderate to fast current.

Emergence: July 1-8

Emergence: First week May through second week August

(described for lata and synonyms cornutella/longicornis/cornuta, as well as walkeri)

The eastern BWOs appear on stream from early May to mid-August, with eastern species, influenced by a more temperate climate ,producing hatches several weeks before the same species on midwestern waters.

Several days before the duns' emergenc,e the nymphs begin a migration from fast open waters to slower currents.

Emergence may take place randomly anywhere from the riverbed to the water's surface. Subsurface emergers are buoyed to the surface by tiny gas bubbles trapped between the folded wing tissue to arrive at the surface with their wings in a wet and bedraggled state, whereas surface emergers are more prepared for flight. Because of such random emergences, many duns, especially those emerging during spells of cool weather, drift considerable distances downstream befor etheir wings are sufficiently dry and rigid for flight.

Eastern BWOs usually emerge during the morning hours as the river is warming from its overnight lows.

When the nymph, emerger, and adult stages of the eastern BWOs are presented to the trout as a food source, a definite preference is directed toward the emerging dun.

The dun's body darkens rapidly on exposure to air and continues to darken during its downstream drift and while maturing on streamside vegetation. Such color transformations are often confusing to the uninformed fly fisher and may result in the sue of a darker eastern BWO imitation than what the trout are actually feeding on.

The actual importance of any eastern BWO hatch is determined by the absence of other mayflies on the water.

(discussed specifically)

Male D. lata spinners gather in swarms about an hour before dusk to court the females over riffly sections of the stream. AFter completing the mating act and resting, the females begin egg-laying just as dusk approaches and oftne produce impressive spinner falls that last for about thirty minutes. The spinner fall is especially important for the fly fisher during the last days of July, when other mayfly species are absent from the water.

(discusses the lata synonyms together with walkeri)

Common name: Eastern Blue-Winged Olives

With few exceptions, large populations of all five species inhabit the gravelly bottome,d fast-water sections of both rivers and streams.

On those rivers and streams where Eastern BWO thrive, hatching activity begins in May and continues into early September.

They get within inches of the surface before suddenly stopping short and then slowly drifting back down to the bottom. After several failed attempts, the nymphs finally reach the surface.

The trout take the helpless nymphs as they swim toward the friend and greedily feed on the nymphs as they are emerging, suspended below the surface film.

In typical mayfly fashion, Eastern BWO spinners return to the stream within twenty-four hours after emergence. Normally they reach the stream at dusk. But depending on conditions, the spinners may not hit the water until late evening, well after dark. Eastern BWO spinner falls are not hit-or-miss affairs. For the most part, they do not generate much of a response from the trout.

Emergence: July 1 to August 10
Nymph habitat: Gravel riffles in streams of all sizes

Emergence can begin as early as 6:30am and continue until noon, with the peak period occurring from 7 to 9am. The duns appear sporadically over an extended period, rarely hatching in large numbers at one time.

The nymphal imitation is sometimes effective before any surface activity is noticed. As the hatch commences, an emerging pattern is productive when floating in the film dead-drift.

The spinners of Drunella lata return just before sundown and fall for almost an hour after dark, providing tremendous evening fishing.

The spinners are far more important than the duns for two reason. First, the duns hatch sporadically over a 4- or 5-hour period in the morning, resulting in a low-intensity emergence and slow feeding activity. Second, the duns must compete with other more numerous species.

FROM CAUCCI & NASTASI (2004):
Finally, we believe that cornuta's obscurity was due to a simple case of mistaken identity. We are convinced that even the most serious experts have mistaken the activity of cornuta for that of Ephemerella attenuata.

This got my attention. What does everyone think about this speculation? Has anyone followed up on this? It seems possible to me.

Finally, we believe that cornuta’s obscurity was also due to a simple case of mistaken identity. We are convinced that even the most serious experts have mistaken the activity of cornuta for that of Ephemerella attemuata. Both are typical of the Blue-Winged Olive varieties that hatch in the morning hours during the season. To get to the base of the angler’s identification problem, let’s scrutinize these similarities. To the untrained eye, cornuta and attenuata look alike. Yet, up close, they are physically different and they have different emergence traits. The cornuta dun is larger, averaging about 9 mm, while attenuata averages around 7 mm (a difference of one hook size). Although the wings are identical in color, the olive body hues are each different.
These differences along with the contrasting subsurface emergence traits of attenuata and cornuta causes trout to exercise extreme selectivity to the respective naturals. This selectivity probably explains the lack of success most anglers report during alleged attenuata hatches. Our stream research indicates, surprisingly, that cornuta is much more prolific on Eastern streams than is the more publicized attenuata. Therefore, in most cases when anglers believe that trout are rising to attenuata duns, they are in reality probably taking the larger and darker cornuta mayflies.

As mature nymphs, and under magnification, their frontal horn differences are quite distinctive.