Hex Mayflies
Hexagenia limbata
The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
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This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
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Stonefly Family Nemouridae (Forestflies)
Where & when
Time of year : Late winter to mid-spring
In 357 records from GBIF, adults of this family have mostly been collected during April (27%), May (22%), March (15%), June (15%), July (8%), and February (6%).
In 120 records from GBIF, this family has been collected at elevations ranging from 20 to 11135 ft, with an average (median) of 6070 ft.
Family Range
Specimens of the Stonefly Family Nemouridae
1 Male Adult
This is the smallest stonefly I've ever collected, with a body only 5.5 mm long.
Although not in-focus in my pictures, its first tarsal segment is similar in length to the third, while the second is much shorter. This helps with family-level identification.
Examining this specimen under a microscope shows a membranous lobe on the dorsal base of the cerci, which is the key characteristic in Merritt & Cummins (4th ed.) to place the genus definitively as Malenka.
Following the species key in Jewett Jr's Stoneflies of the Pacific Northwest, the species appears to be Malenka tina. My dissecting microscope seems to show sternite 9 ending in a rounded knob, which distinguishes it from Malenka bifurcata, but the detail is hard to work out.
Also worth noting is that Montana appears to have this species, whereas birfucata is not know there: http://fieldguide.mt.gov/displaySpecies.aspx?family=Nemouridae
Although not in-focus in my pictures, its first tarsal segment is similar in length to the third, while the second is much shorter. This helps with family-level identification.
Examining this specimen under a microscope shows a membranous lobe on the dorsal base of the cerci, which is the key characteristic in Merritt & Cummins (4th ed.) to place the genus definitively as Malenka.
Following the species key in Jewett Jr's Stoneflies of the Pacific Northwest, the species appears to be Malenka tina. My dissecting microscope seems to show sternite 9 ending in a rounded knob, which distinguishes it from Malenka bifurcata, but the detail is hard to work out.
Also worth noting is that Montana appears to have this species, whereas birfucata is not know there: http://fieldguide.mt.gov/displaySpecies.aspx?family=Nemouridae
3 Female Adults
A few of these tiny stoneflies were among the only species of aquatic insect adults in the air on this particular afternoon, with most of the action coming from a species of Epeorus mayfly. I somehow forgot to photograph this one on the usual ruler, but I recall it was very, very small, with an abdomen no more than 1mm in girth and the body, not counting the wings, probably just 5-7mm long.
From N. Touchet River at Touchet Corral.
1 Adult
2 Nymphs
Nymphs of this species were fairly common in late-winter kick net samples from the upper Yakima River. Although I could not find a key to species of Zapada nymphs, a revision of the Nemouridae family by Baumann (1975) includes the following helpful sentence: "2 cervical gills on each side of midline, 1 arising inside and 1 outside of lateral cervical sclerites, usually single and elongate, sometimes constricted but with 3 or 4 branches arising beyond gill base in Zapada cinctipes." This specimen clearly has the branches and is within the range of that species.
Discussions of Nemouridae
deligon
2 replies
Posted by Deligon on Jan 15, 2010
Last reply on Jan 22, 2010 by Martinlf
FISHED THE HIWASSEE RIVER IN TENN , TODAY JAN 15 2010 WEATHER HIGH 50,S
AFTER A COUPLE OF WEEKS OF TEMPS IN THE TEENS, EXPECTED MIDGE HATCH,
WE HAVE A SHAD KILL WHICH I WANTED TO FISH STREAMERS HOPING TO TAG A BIG BROWN. BUT THE WINTER STONEFLY HATCH TOOK THE SHOW. DRY FLY FISHING IN JAN. WHAT IS THE LIFE CYCLE OF THESE FLIES? CAN THEY TOLERATE THE COLD NIGHT TEMPS? DO THEY EAT AND DRINK? WHOW DO THEY MATE?
THE MORE I LEARN THE MORE I DISCOVER I DON'T KNOW
DELIGON
AFTER A COUPLE OF WEEKS OF TEMPS IN THE TEENS, EXPECTED MIDGE HATCH,
WE HAVE A SHAD KILL WHICH I WANTED TO FISH STREAMERS HOPING TO TAG A BIG BROWN. BUT THE WINTER STONEFLY HATCH TOOK THE SHOW. DRY FLY FISHING IN JAN. WHAT IS THE LIFE CYCLE OF THESE FLIES? CAN THEY TOLERATE THE COLD NIGHT TEMPS? DO THEY EAT AND DRINK? WHOW DO THEY MATE?
THE MORE I LEARN THE MORE I DISCOVER I DON'T KNOW
DELIGON
Start a Discussion of Nemouridae
References
- Baumann, Richard W. 1975. Revision of the Stonefly Family Nemouridae (plecoptera) : a Study Of The World Fauna At The Generic Level. Smithsonian Contributions to Zoology undef(211): 1-74.
- Merritt R.W., Cummins, K.W., and Berg, M.B. 2019. An Introduction to the Aquatic Insects of North America (Fifth Edition). Kendall/Hunt Publishing Company.
- Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.
Stonefly Family Nemouridae (Forestflies)
Taxonomy
6 genera (Lednia, Nanonemoura, Ostrocerca, Paranemoura, Shipsa, and Visoka) aren't included.