Westside river insect ID help


Active Member
I've been meaning to post this pic for some time. It's what looks to be a stonefly of some kind. Here's the link to the gallery pic: http://www.washingtonflyfishing.com/gallery/showphoto.php?photo=5436&cat=514&page=1
I found it, along with a large mayfly (two other pics in the freshwater fish food gallery), http://www.washingtonflyfishing.com/gallery/showphoto.php?photo=5437&cat=514&page=1 in a westside river that some have declared "unfishable" due to the color of the water. Still, I found it interesting to see a yellow stonefly on this side of the Cascades. Anyone have some knowledge to share?


Active Member
Yellow Sallies certainly occur on the west side, as do the small stoneflies that some call the "Lime Sally', about the same size but of a pale green color. A fly that I was surprised to find was an adult Hexagenia down low on the Snoqualmie near its confluence with the Skykomish. It was the biggest damned mayfly I've ever seen; nearly three inches from head to tail.


Active Member
A Hex, no less? A couple of years ago, I was leaving a zipper-lipped lake near Monroe at around sunset. To my surprise, I started seeing these huge mayflies taking to the air. Yes, about three inches. There was no mistaking they were mayflies, as their forked tails were clearly visible in the fading light. To this day, I keep wondering if they might have been Hexs. I suppose that if you saw some down at the sno/sky confluence, there's no reason why my lake mays couldn't be the same. Interesting, no?


Active Member
Hexes are an annual occurrence at Merrill Lake in Lewis County but I don't recall hearing reports (other than yours) of them at any other Washington lakes. The one I fished out of the Snoqualmie was already dead and floating, and I assumed that since hexes are burrowers in muddy bottoms that it was a river resident (since the Snoqualmie is pretty slow with more mud than gravel down there). Interesting, anyone have any other hex spottings to report?
When I was an undergrad, I worked with a group researching stream water quality. There is information out there that linked the number and variety of aquatic insects with the relative health of a stream. Pretty interesting stuff. While we did most of our sampling on the east side of the state, we also did a bunch of sampling on the wet side. I can attest the we found all sorts of genera of stonefiles over here on the west side. Incedentally, the water quality thing seemed to have been influenced more by the types and numbers of mayflies in a stream than stoneflies (or any other group for that matter). The mayfly in your pic looks like an Ephemerella mayfly.

The big mayfies you saw on the lake were most probably hexagenia (giant mayflies). It's been a few years since I took aquatic entomology, so don't quote me on this, but I believe that members of Hexagenia prefer still to slow moving water. Our lakes do get some relatively small hex hatches during the summertime. I've had a few good evenings fishing this hatch with a hex emerger on my local lake. It's good fun just to watch the fish slam these huge beasts off the water surface.


Old Man

Just an Old Man
Well I know absolutly nothing about bugs of any kind. But I did find a couple of bugs under a bridge on the Foss river that were quite big. All that was there was the outer skin(don't know what it's called) and they were up to at least 2 1/2" long. All I know is that I don't want them diving at me.

those were most likely stonefly exoskeletons under the bridge. if they were really 2.5 inches long, they could have been pteronarcids (giant stonefly). when we were sampling we quite often found them in small streams and creeks that were sometimes just barely a trickle.

here's a link to some info. http://www.origins.tv/entomology/stories/BotW3.7.04GiantStonefly.htm

If you've seen one in real life, you'll know that the stonefly in the picture is just about actual size.

As Sci-Fly said, Hexagenia are known to hatch from Padden and Whatcom Lakes. As burrowing mayflies, they're likeliest to occur in silt-bottom lake shallows. Emergence here occurs in July and August.