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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As far as I can tell, this species has only previously been reported from one site in Oregon along the Columbia gorge. However, the key characteristics are fairly unmistakable in all except for one minor detail:
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
— 4 small yellow spots on frons visible in photos
— Narrow occipital spinule row curves forward (but doesn’t quite meet on stem of ecdysial suture, as it's supposed to in this species)
— Short spinules on anterior margin of front legs
— Short rposterior row of blunt spinules on abdominal tergae, rather than elongated spinules dorsally
I caught several of these mature nymphs in the fishless, tiny headwaters of a creek high in the Wenatchee Mountains.
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Caddisfly Genus Hydatophylax (Giant Cream Pattern-Wing Sedges)
These are huge caddisflies. The larvae may be nearly an inch and a half long and build three-inch cases. Hook sizes 4-6 are appropriate for the pupae.
Where & when
Time of year : Late May to fall in the East; August to October in the West
Preferred waters: Medium to large streams
In 69 records from GBIF, adults of this genus have mostly been collected during June (46%), July (22%), May (19%), and August (7%).
In 14 records from GBIF, this genus has been collected at elevations ranging from 33 to 2740 ft, with an average (median) of 2008 ft.
Genus Range
Egg-Laying behavior
The egg-laying adults are not important.Larva & pupa biology
Diet: Woody debris
Current speed: Slow
Specimens of the Caddisfly Genus Hydatophylax
1 Female Adult
I had some trouble working through the genus key for this one because I'm not great at interpreting caddis wing venation. Fortunately, figure 19.707 in An Introduction to the Aquatic Insects of North America (Fifth Edition) shows the distinctive color pattern of the striking forewings on Hydatophylax argus, which is a perfect match for the pattern as well as venation. As there are no other species in that genus in this area, I can be pretty confident in the species ID.
Start a Discussion of Hydatophylax
References
- 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 Genus Hydatophylax (Giant Cream Pattern-Wing Sedges)
Taxonomy
Species in Hydatophylax: Hydatophylax argus, Hydatophylax hesperus
2 species (Hydatophylax variabilis and Hydatophylax victor) aren't included.