Mahogany Duns

This is by far the most important species of Isonychia. Many angling books once split its credit with the species Isonychia sadleri and Isonychia harperi, but entomologists have since discovered that those are just variations of this abundant species.

See the main Isonychia page for more about these intriguing mayflies.

This important Western species is one of the few mayflies outside the Ephemeridae family to possess large tusks on the front of its head. It is also one of the largest species of Paraleptophlebia.

P. bicornuta is often reinforced by simultaneous hatches of the more common Paraleptophlebia debilis. The two duns appear virtually identical to the naked eye, though bicornuta usually has an edge in size.

Paraleptophlebia bicornuta is by far the widest distributed tusked species, though there are others. Telling the tusked species apart is very difficult and even entomological texts are largely ambiguous on the characters that differentiate them. Distribution records are probably the most reliable way for anglers to know with any probability what they are looking at. Check out the Paraleptophlebia packii and Paraleptophlebia helena hatch pages for more distribution information.

This widespread species can produce memorable hatches where it is locally abundant, especially in the West where it also tends to run larger in size. It loves the margins as is typical of most Leptophlebiidae species but has a greater tolerance for current. They are often found even in riffles. This is the most important species in the West.

This large species of Paraleptophlebia is one of the tusked group. Records indicate it is endemic (Endemic: where found; native to; belonging exclusively to or confined to a particular place) to California where it fills the niche taken by Paraleptophlebia bicornuta in neighboring states. It usually hatches with the more common and very similar looking duns of Paraleptophlebia debilis.

This large western species is common in places. It is one of the few that has tusks and substitutes for the more common tusked Paraleptophlebia bicornuta in some locales, particularly the central Rockies in parts of Colorado, Utah, and Wyoming where they have been documented. Telling the tusked species apart is very difficult and even entomological texts are largely ambiguous on the characters that differentiate the nymphs. Angling texts relying on gill morphology (Morphology: The form and structure of an organism, or the study of the form and structure of organisms.), terga pattern, and tusk shape are dubious at best. For now, the angler's best bet is to rely somewhat on documented distribution.

This species may reinforce hatches of Paraleptophlebia debilis.

There are many species in this genus of mayflies, and some of them produce excellent hatches. Commonly known as Blue Quills or Mahogany Duns, they include some of the first mayflies to hatch in the Spring and some of the last to finish in the Fall.

In the East and Midwest, their small size (16 to 20, but mostly 18's) makes them difficult to match with old techniques. In the 1950s Ernest Schwiebert wrote in Matching the Hatch:

"The Paraleptophlebia hatches are the seasonal Waterloo of most anglers, for without fine tippets and tiny flies an empty basket is assured."

Fortunately, modern anglers with experience fishing hatches of tiny Baetis and Tricorythodes mayflies are better prepared for eastern Paraleptophlebia. It's hard to make sense of so many species, but only one is very important and others can be considered in groups because they often hatch together:

• Paraleptophlebia adoptiva is by far the most important species of this genus in the two regions and is an early Spring emerger.


• Paraleptophlebia mollis, Paraleptophlebia guttata, and Paraleptophlebia strigula complement each other in late spring and early summer.


• Paraleptophlebia debilis and Paraleptophlebia praepedita occur together in the fall.

In the West, it is a different story. For starters the species run much larger and can be imitated with flies as large as size 12, often size 14, and rarely smaller than 16. Another difference is the West has species with tusks! Many anglers upon first seeing them think they are immature burrowing nymphs of the species Ephemera simulans aka Brown Drake. With their large tusks, feathery gills, and slender uniform build, it's an easy mistake to make. Using groups again:

• The most important species is Paraleptophlebia debilis. This large (for the genus) Fall emerger can be found throughout the region. It is often accompanied by one of the slightly larger tusked species. Depending on locale, this can be Paraleptophlebia bicornuta (the most common), Paraleptophlebia packii or Paraleptophlebia helena. Check out their hatch pages for distribution information.


• Spring is the season for the smaller Paraleptophlebia heteronea throughout most of the region with Paraleptophlebia gregalis filling this niche in California and parts of Oregon.