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.
|Option 1||Option 2|
|Mesonotum enlarged to form a shield extended to abdominal segment VI (in other words, they look like they're wearing a turtle shell) ||Mesonotum not enlarged as above|
|Abdominal gills enclosed beneath shield||At least some abdominal gills exposed|
|Remaining families: Acanthametropodidae, Ameletidae, Ametropodidae, Arthropleidae, Baetidae, Behningiidae, Caenidae, Ephemerellidae, Ephemeridae, Euthyplociidae, Heptageniidae, Isonychiidae, Leptohyphidae, Leptophlebiidae, Metretopodidae, Neoephemeridae, Oligoneuriidae, Palingeniidae, Polymitarcyidae, Potamanthidae, Pseudironidae, and Siphlonuridae|
5 Example Specimens
I took a few group picture of a bunch of Baetisca laurentina nymphs to show the degree of individual variation in size, color, and shape that can occur within the same species in the same pool of the same river. This variation is one important reason why trout are forgiving of some small degree of variation in our imitations--the naturals themselves vary, too.
5 Example Specimens
This Isonychia bicolor nymph from the Catskills displays the prominent white stripe sometimes characteristic of its species. This is the first such specimen I've photographed, because members of the same species in the Upper Midwest have a more subdued stripe (and were once thought to be a different species, Isonychia sadleri). The striking coloration on this eastern nymph is more appealing.
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.
I caught this Ameletus nymph with several others of the same kind. This was the most vivid example, but they all had quite a bit of striking and unusual red shading, especially on the last few abdominal segments.
I keyed it out under the microscope using Larvae and adults of Ameletus mayflies (Ephemeroptera: Ameletidae) from Alberta with slightly larger (10 mm), mature specimen with darkened wingpads. Microscope pictures are from that specimen. The characteristics in the key and most of the verification table point pretty clearly to Ameletus cooki, except that the coloration of the antennae more closely resembles Ameletus sparsatus. However, on other characteristics in which these species differ (spines on the dorsal surface of the front femora, which seem very short in this specimen; length of posterolateral spines on segments 8–9; length of spines on posterior edge of tergites 6–9), this is a better match for cooki, and that's probably the correct ID.
|Go to Couplet 2|