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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Caddisfly Family Rhyacophilidae (Green Sedges)
See Rhyacophila for details. It is an extremely important trout stream genus, containing well over 100 American species.
The other genus, Himalopsyche, contains only one relatively unimportant American species.
The other genus, Himalopsyche, contains only one relatively unimportant American species.
Where & when
In 1217 records from GBIF, adults of this family have mostly been collected during June (24%), July (21%), May (18%), August (17%), September (7%), and April (6%).
In 610 records from GBIF, this family has been collected at elevations ranging from 10 to 23622 ft, with an average (median) of 3652 ft.
Family Range
Identification
To further identify a specimen of Rhyacophilidae to the genus level, use the Key to Genera of Rhyacophilidae Adults.
Specimens of the Caddisfly Family Rhyacophilidae
1 Adult
3 Pupae
This was a neat, rare view into a Rhyacophila caddisfly just beginning to pupate, with the features of the larva still clearly visible inside.
I collected this pupa and several like it from the same stream and on the same day as this larva. I suspect they're the same species. Every pupa I collected was in a brown casing like the one shown in one of the pictures below. I cut this pupa out of its case after a picture so you can see more details. It is close to but not fully developed.
Even though I already have pictures of a Rhyacophila pupa in its cocoon, I took this one and then tried to keep the pupa alive, hoping to photograph it in several stages of development. That didn't work out; it seems to have died without changing much. Oh well.
9 Larvae
This specimen is very tentatively placed in Rhyacophila vocala, but see the caveats given by Dave Ruiter in its identification: "There are two species (hyalinata and vocala) currently within the group and this looks closest to R. vocala. It is likely, however, there are several undescribed species in the group and this is one of those."
Dave Ruiter identified this specimen as part of the Rhyacophila betteni group, but with over 20 species it's difficult to narrow down beyond that.
This specimens shows that the name "green rockworm" doesn't quite fit all Rhyacophila larvae, even though it does fit the majority. This is actually the first of their larvae that I've found in a different color. I'm not sure if it's because of the species or because this is a young one, but I have found equally small green larvae, so I'm guessing it's the species.
This is the first Rhyacophila larva I've seen with this striking black banded appearance. I caught several larvae of this species in a fast riffle in a mid-sized trout stream.
I collected this larva and several like it from the same stream and on the same day as this pupa. I suspect they're the same species.
Start a Discussion of Rhyacophilidae
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.
- LaFontaine, Gary. 1981. Caddisflies. The Lyons Press.
- 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.
Caddisfly Family Rhyacophilidae (Green Sedges)
Taxonomy
Genus in Rhyacophilidae: Himalopsyche, Rhyacophila
