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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
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.

Lateral view of a Onocosmoecus (Limnephilidae) (Great Late-Summer Sedge) Caddisfly Larva from the Yakima River in Washington
This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Giant Water Bug Species Belostoma flumineum (Electric Light Bugs)

Where & when

In 141 records from GBIF, adults of this species have mostly been collected during September (18%), August (15%), October (15%), July (13%), May (12%), and June (11%).

In 12 records from GBIF, this species has been collected at elevations ranging from 246 to 1083 ft, with an average (median) of 620 ft.

Specimens of the Giant Water Bug Species Belostoma flumineum

2 Adults

Discussions of Belostoma flumineum

Anyone else find these to be important?
2 replies
Posted by Troutnut on Jul 26, 2006
Last reply on Oct 9, 2006 by GONZO
Back when I was just starting to learn to fly fish and still kept quite a few fish, I autopsied the stomachs of a couple 17-19 inch brown trout in August and found them packed with these Belostoma flumineum bugs.

I haven't tied a reasonable imitation yet, but if those fish (from a few miles apart on the same river) were so fond of them an imitation is probably a great idea. It would be good to figure out where and when these things are important.

None of the fly fishing literatue I've seen has dealt with them at all, except for mentioning their existence in passing.

Start a Discussion of Belostoma flumineum

Giant Water Bug Species Belostoma flumineum (Electric Light Bugs)

Taxonomy
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