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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Amphizoa (Amphizoidae) Beetle Larva from Sears Creek in Washington
This is the first of it's family I've seen, collected from a tiny, fishless stream in the Cascades. The three species of this genus all live in the Northwest and are predators that primarily eat stonefly nymphs Merritt R.W., Cummins, K.W., and Berg, M.B. (2019).
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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Caddisfly Genus Arctopsyche (Great Gray Spotted Sedges)

Arctopsyche grandis, the western species, is by far the most important in this genus. It produces excellent fishable hatches.

Where & when

In 132 records from GBIF, adults of this genus have mostly been collected during July (39%), June (37%), and August (13%).

In 281 records from GBIF, this genus has been collected at elevations ranging from -30 to 19701 ft, with an average (median) of 1365 ft.

Genus Range

Larva & pupa biology

Diet: Smaller insects

Shelter type: They spin and tend their nets instead of building a case.

The larvae live for two years before emerging and are especially prone to behavioral drift at dawn and dusk.

Specimens of the Caddisfly Genus Arctopsyche

2 Larvae

Discussions of Arctopsyche

Arctopsyche grandis in waterton canyon
1 replies
Posted by Krikut on May 16, 2016 in the species Arctopsyche grandis
Last reply on May 17, 2016 by Bnorikane
Discovered one of these guys or (gals?) back on March 20 of this year up in Waterton Canyon. He was so chunky I first thought it was a small hellgrammite (I grew up in Virginia, where the hellgrammite was the bug of choice in most smallmouth rivers). This particular one measured about half an inch and had a bright green tail/foot segment. I'm curious if you guys have a favorite immitation? Thanks!
Arctopsyche Grandis
6 replies
Posted by Epeorus on Jul 2, 2014
Last reply on Jul 6, 2014 by Entoman
A while ago there was some discussion of this bug in Colorado. I first came across this beast in early July 2011 on the Eagle River, just downstream of Edwards, Co. Met him again this week on the Eagle. It's quite the blast - big bugs and big trout. Especially the ones rising with abandon in the fast water in the middle of the day.

Funny thing is we don't seem to see these guys most years. The commonality between 2011 and this year is an extended runoff leading to cold and high - though clear water in early July. I wonder if they normally hatch during the peak of the runoff when no one is on the water.

I remember people commenting about these caddis allegedly being in parts of Colorado. The hatches the last two days on the Eagle and what I saw in 2011 would add some level of credence to that belief.

A size 10 (on a Partridge L3A) sponge body caddis with a dark gray body, and a size 10 Lafontaine sparkle emerger with a gray body and a clear shroud were the ticket.
Arctopsyche grandis
6 replies
Posted by Flymonster on Sep 7, 2011 in the species Arctopsyche grandis
Last reply on May 20, 2013 by Flymonster
Here in the Willamette Valley the McKenzie Caddis (as Arctopsyche grandis is known locally) usually begins its emergence sometime around mid-May and can continue into mid-June. The most emergence activity will be noted on warm days once the water temperature reaches @ 52f. Most hatches occur on warm sunny days from 4pm-7pm. Arlen Thomason goes into great detail about the life-cycle and behaviors of a. grandis in his book "Bug Water".

At least for me, the McKenzie Caddis, marks the beginning of summer and excellent fly fishing for trout on the McKenzie, Middle Fork Willamette, North Fork of the Middle Fork Willamette, and our other local rivers and streams.

Start a Discussion of Arctopsyche


Caddisfly Genus Arctopsyche (Great Gray Spotted Sedges)

Species in Arctopsyche: Arctopsyche grandis, Arctopsyche irrorata
2 species (Arctopsyche californica and Arctopsyche ladogensis) aren't included.
Genus Range
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