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Caddisfly Species Arctopsyche grandis (Great Gray Spotted Sedge)

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Common Name
MatchCommon Name
***Great Gray Spotted Sedge
Pictures Below
Gary LaFontaine regarded this species as very important in the West, and wrote of it in Caddisflies:

A. grandis is one of those special insects that is worth making the focus of a fishing trip because it gets the best trout in a river interested in feeding.

It owes much of its importance to its large size.

Where & When

Region: West

Time Of Year (?): July

Preferred Waters: Mountain streams

Hatching Behavior

Time Of Day (?): Mostly nighttime

Egg-Laying Behavior

Time Of Day: Mostly nighttime

Arctopsyche grandis Fly Fishing Tips

Swisher and Richards remark in Selective Trout that imitations of the large adults make good searching patterns (Searching pattern: Any artificial fly pattern used when trout that aren't feeding selectively on anything in particular. A searching pattern may be an attractor or an imitation of something specific that the fish might favor even though it's not currently hatching.).

Pictures of 1 Caddisfly Specimen in the Species Arctopsyche grandis:

Arctopsyche grandis (Great Gray Spotted Sedge) Caddisfly LarvaArctopsyche grandis (Great Gray Spotted Sedge) Caddisfly Larva View 14 PicturesAt first I had trouble believing this giant Hydropsychidae larva was actually a member of its family, because of the size. I had never seen such a thing. It turned out to be a member of this exceptionally large species with a fitting name, grandis.
Collected August 3, 2020 from the East Fork Big Lost River in Idaho
Added to by Troutnut on August 19, 2020

Recent Discussions of Arctopsyche grandis

Arctopsyche grandis in waterton canyon 1 Reply »
Posted by Krikut on May 16, 2016
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!
ReplyArctopsyche grandis 6 Replies »
Posted by Flymonster on Sep 8, 2011
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.

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