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 an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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Alderfly Genus Sialis
Alderflies are typically mistaken for small hellgrammites as larvae and large caddisflies as adults. They turn up often enough in nymph samples that it's nice to know what they look like. There are rumors of their occasional importance to trout, but the average anglers is not likely to encounter it.
Genus Range
Egg-Laying behavior
Time of day: Daytime
They lay their eggs on dry objects near the water. Ernest Schwiebert describes their egg placement in Matching the Hatch:
The egg masses are deposited on rocks, limbs, leaves and bridges where they are over running water and in the sunlight. They are placed so that the hatching larvae fall into the stream.
Larva & pupa biology
Current speed: Slow
Substrate: Silt
Specimens of the Alderfly Genus Sialis
1 Male Adult
4 Larvae
Start a Discussion of Sialis
References
- Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.
- 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.
- Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.
Alderfly Genus Sialis
Taxonomy
Species in Sialis
Sialis hamata
1
2
Species in Sialis: Sialis hamata
23 species (Sialis aequalis, Sialis americana, Sialis arvalis, Sialis bilobata, Sialis californica, Sialis concava, Sialis contigua, Sialis cornuta, Sialis dreisbachi, Sialis glabella, Sialis hasta, Sialis infumata, Sialis iola, Sialis itasca, Sialis joppa, Sialis mohri, Sialis nevadensis, Sialis nina, Sialis occidens, Sialis rotunda, Sialis spangleri, Sialis vagans, and Sialis velata) aren't included.