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 a striking caddis larva with an interesting color pattern on the head. Here are some characteristics I was able to see under the microscope, but could not easily expose for a picture:
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
- The prosternal horn is present.
- The mandible is clearly toothed, not formed into a uniform scraper blade.
- The seems to be only 2 major setae on the ventral edge of the hind femur.
- Chloride epithelia seem to be absent from the dorsal side of any abdominal segments.
Based on these characteristics and the ones more easily visible from the pictures, this seems to be Grammotaulius. The key's description of the case is spot-on: "Case cylindrical, made of longitudinally arranged sedge or similar leaves," as is the description of the markings on the head, "Dorsum of head light brownish yellow with numerous discrete, small, dark spots." The spot pattern on the head is a very good match to figure 19.312 of Merritt R.W., Cummins, K.W., and Berg, M.B. (2019). The species ID is based on Grammotaulius betteni being the only species of this genus known in Washington state.
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CalebBoyle has attached these 2 pictures to aid in identification. The message is below.
CalebBoyle on May 23, 2007May 23rd, 2007, 2:27 pm EDT
Hi guys,
I found this female mayfly near where I live and wanted to see what you all thought about it. It was found in gaston county (near Charlotte) in North Carolina. When I first glanced at it I thought it must be some kind of drake, but quickly realized it couldn't be. There are only 2 tails and this monster is 36-37mm long. I have never heard of Hexagenia in North Carolina, but isn't this a H. limbata? If so what records are there for NC hatches and how common are they? Most of the pictures that I have seen of limbata have darker markings on the abdomen, but then what other mayfly is this size other than a Litobrancha recurvata?
Caleb Boyle
I found this female mayfly near where I live and wanted to see what you all thought about it. It was found in gaston county (near Charlotte) in North Carolina. When I first glanced at it I thought it must be some kind of drake, but quickly realized it couldn't be. There are only 2 tails and this monster is 36-37mm long. I have never heard of Hexagenia in North Carolina, but isn't this a H. limbata? If so what records are there for NC hatches and how common are they? Most of the pictures that I have seen of limbata have darker markings on the abdomen, but then what other mayfly is this size other than a Litobrancha recurvata?
Caleb Boyle
Taxon on May 23, 2007May 23rd, 2007, 3:03 pm EDT
Nice photos, Caleb. You have (3) Hexagenia species in N. Carolina, H. atrocaudata, H. bilineata, and H. limbata. However, given its size and date of emergence, it is almost certainly H. limbata. Incidentally, notice the characteristic vestigal terminal filament! That is one I've been saving for you, Gonzo.
Troutnut on May 23, 2007May 23rd, 2007, 3:20 pm EDT
It's H. limbata. That's a widely variable species, and back in the 1940s it was actually broken into about 6 sub-species with different looks and geographic ranges. The sub-species aren't considered valid anymore (it's all just one undivided species now, I think) but the point is that H. limbata comes in many flavors.
Somebody recently emailed me asking me to identify one from Texas, too.
Somebody recently emailed me asking me to identify one from Texas, too.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
Troutnut and salmonid ecologist
GONZO on May 23, 2007May 23rd, 2007, 4:08 pm EDT
Roger--Thanks for the terminal filament reference. You've been saving that one for a while!
Caleb--Beautiful specimen! The variability in color/markings that Jason mentions always amazes me when I view specimens of this transcontinental species.
Caleb--Beautiful specimen! The variability in color/markings that Jason mentions always amazes me when I view specimens of this transcontinental species.
CalebBoyle on May 24, 2007May 24th, 2007, 8:43 am EDT
Thanks guys for the confirmations-- I had just never heard about limbata this far south. I agree Gonzo, I have seen some photos of color variations that are really different.
Caleb
Caleb
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