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.
Where & when
Time of year : September through early November
Time of day : Morning and afternoon
Specimens of the Mayfly Species Paraleptophlebia bicornuta
This species is interesting because it is common in lakes as well as streams. It is one of the last species of the year to emerge in western Montana. Adults have been collected as late as October 15 weather permitting.