Blue-Winged Olives

"These little critters supplant the importance of many other well-known mayfly hatches."

-Fred Arbona in Mayflies, the Angler, and the Trout

Arbona did not overestimate these critters. Their great numbers and multiple broods each season make up for their size, which is rarely larger than 16 and usually smaller than 18.

Entomologists seem to be perpetually reclassifying the species of this family. Only the stillwater genus Callibaetis is free from the confusion, as its most important species have been combined under the name Callibaetis ferrugineus.

Aside from that species, fishable Baetidae hatches nationwide are mostly likey to come from the species Baetis tricaudatus, Baetis brunneicolor, Baetis flavistriga, Diphetor hageni, and Acentrella turbida. In the West, Plauditus punctiventris joins the list. In the East and the Midwest, look for Baetis intercalaris and Plauditus dubius. The important species Heterocloeon anoka is exclusive to the Midwest.

Identification of these mayflies is difficult, and many of the lesser-known species probably produce excellent local hatches but have not caught the attention of anyone who can identify them. This is especially likely in the Southwest. The lesson is that we should not assume anything about the identity of a Baetidae hatch; it is not necessarily Baetis, and it may not be any familiar species.

This genus contains exciting hatches for both Eastern and Western fishermen. Drunella lata creates the lengthy Large Blue-Winged-Olive hatches on Eastern and Midwestern mornings, and their spinners are important in the Midwest. In the West, Drunella grandis and Drunella doddsii generate the Western Green Drake hatches.

Although by no means a superhatch, this species can be important. Authors who discuss it lament the general lack of credit it receives for the fine hatches it produces on some streams.

This intriguing species has received a lot of attention in past angling books. Recent authors suspect that much of this credit was a case of mistaken identity, with Attenella attenuata receiving praise for the hatches of Drunella lata and Dannella simplex. Much of the credit was legitimate and accurate, but this species is no longer thought to be on par with its most popular cousins in Ephemerella and Drunella.

I have several specimens listed under this species, but I'm not positive the identification is correct.

This species is best known for the summer morning action it creates in the East and Midwest. It is prolific but the emergence is often sporadic and sparse, which means it is often upstaged by blizzards of tiny Tricorythodes mayflies and other more concentrated hatches.

Recent taxonomic changes have served this species well, because several other popular species (Drunella cornuta, Drunella cornutella, and Drunella longicornis) are now recognized as synonyms (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) of Drunella lata. The combined lata hatch now lasts for months.

Angling entomology books show several differences in hatching behavior between the former species now combined with lata. I've tried to parse these into a coherent picture here based on the geography of the old species, but I recommend consulting experienced local anglers to understand which of the many variations on lata behavior is prevalent in your area.

This is the second most common East-Midwest Drunella species, but it is not very important compared to Drunella lata. Ernest Schwiebert had this to say about their hatches:

An imitation is rarely required, but notes show that when it is needed it is needed badly.

A cult following is something to which few insects can lay claim, but the tiny Tricorythodes mayflies certainly qualify. Their widespread, reliable, heavy hatches draw impressive rises of ultra-selective trout which demand the most of a technical dry-fly angler's skills.

It is surprising that such a great hatch took so long to come to the attention of fly fishermen. The Tricos were first introduced to anglers in a 1969 Outdoor Life article by Vincent Marinaro, who misidentified them as Caenis. By the early 1970s the identification had been corrected but Swisher and Richards still wrote in Selective Trout, "Few anglers are familiar with these extremely small but important mayflies." The next wave of publications boosted Tricorythodes to its current fame. I suspect their early dismissal was due in part to tackle limitations; anglers in the 1950s had no means to effectively tie and present size 22-28 flies.

Until recently, Ephemerella excrucians was a widespread species of relatively minor importance. Recent work by entomologists uncovered that it is the same species as the important Western Pale Morning Duns Ephemerella inermis, and the two combined took the name of excrucians.

The behavioral information I've given below is tentative. Because of the taxonomic shuffling and the fact that books usually describe this species together with others, it is a little bit unclear which writings specifically apply to excrucians.

The Flavs pick up about a week after the closely related but larger Western Green Drakes (Drunella grandis and Drunella doddsii) finish hatching on most Western waters.

Their hatches may be complemented by simultaneous hatches of two less prolific species, Drunella coloradensis and Drunella spinifera.