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Fly anglers live for the "hatches" when trout erupt in a feeding frenzy over the mass emergence aquatic insects from the river's surface. In these moments, trout can become so focused on one specific type of prey that they will pursue only a skillful imitation. Anglers who study aquatic insects to meet this challenge find that they're as captivating as the fish themselves. Every species has its own story, its own personality. We cross paths with these characters at the climax of a perennial drama of life and death, and--as with any great drama or sport--every play means so much more when we know the players inside and out. It's not just about catching fish. It's about knowing the stream and loving everything in it.'s aquatic insect encyclopedia is a guide to these players and their stories. Read about the behavior of each species and view thousands of closeup photos, or join the fly fishing forum to meet other devotees of the world's healthiest addiction. You can learn the basics of mayflies, caddisflies, or stoneflies. Or dive into the details of storied species like the Hendrickson hatch and the Hex hatch.

Latest updates

The blog posts below describe every update ever added to by myself (Troutnut) and other contributors, along with occasional other thoughts and stories from my adventures in fishing, hunting, research, and travel in Alaska and beyond.

Updates from August 23, 2020

Photos by Troutnut from the Snake River in Idaho

Snake River from the Clark Hill Rest Area on highway 26. Smoke from distant California wildfires was clouding eastern ID / west WY a couple weeks before this year's coast-wide smoke catastrophe. From the Snake River in Idaho.
Snake River from the Clark Hill Rest Area on highway 26. Smoke from distant California wildfires was clouding eastern ID / west WY a couple weeks before this year's coast-wide smoke catastrophe.
LocationSnake River
Date TakenAug 23, 2020
Date AddedSep 18, 2020
CameraCanon EOS 7D Mark II

Closeup insects by Troutnut from the Snake River in Idaho

Male Epeorus (Little Maryatts) Mayfly SpinnerMale Epeorus (Little Maryatts) Mayfly Spinner View 10 PicturesThis spinner appeared inside our car after a rest stop overlooking the Snake, so that's most likely where it came from.
Collected August 23, 2020 from the Snake River in Idaho
Added to by Troutnut on September 18, 2020

Updates from August 22, 2020

Sizable bull trout

By Troutnut on August 16th, 2020, 6:24 pm
On my recent trip through various parts of Montana, Wyoming, and Idaho, I enjoyed tangling with some big, wild bull trout. It was the first time I've caught them on purpose. Because of the sensitivity of the fishery and a promise to the person who told me about the spot(s), I'm only posting the fish pictures -- stripped of any identifying information or metadata -- and omitting anything of the scenery, or even which state I caught them in. Suffice it to say everything was legal, all the fish were released quickly and unharmed, and I had an awesome time. Most were caught on streamers with single barbless hooks. One took a stonefly nymph instead.

The first mature bull trout of the trip was also the biggest I landed, a gorgeous 22" male:

Of the other seven big bulls landed, one was 16" and the rest were 18.5-21". I hooked and lost at least as many, including some that probably would have surpassed the 22-incher.

One of the most memorable moments of the trip came when I was working on a big (about 20") bull I had spied holding under a log draped along one bank in some fast water. It had chased my streamer on the first cast without taking, and it was now sulking below the log, ignoring one fly after another. It was holding in the sun, right on the edge of a deep black shadow created by the log and the undercut bank behind it. I focused like a laser on the fish as I swung various streamers past its nose. On the first cast with one new streamer, I was watching the big fish's lack of reaction when, just inches in front of its nose, the shadows produced into the sunlight the gaping maw of a much larger fish hot on the tail of my Sculpzilla. It pursued the streamer half-way across the pool, then turned around and vanished into the darkness, never to be seen again.

I spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) at least another thirty minutes there and hooked and lost the 20-incher, but there was never another hint of the monster. In my memories of the ones that got away, that giant fish's head slowly emerging from the black shadow into the bright sun will be etched in a timeless frame next to the giant rainbow I lost at the base of the former set of Edoras from the Lord of the Rings movies in New Zealand.

Review of "An Introduction to the Aquatic Insects of North America" 5th Edition by Merritt, Cummins, & Berg

By Troutnut on August 14th, 2020, 10:15 pm
I've been using this book a lot to identify new insect specimens for the last two summers and wanted to share some quick thoughts. An Introduction to the Aquatic Insects of North America is the definitive technical reference for identifying aquatic insects (at least to family or genus level) and has been for decades.

The 5th Edition seems like one of the most significant updates yet, especially for mayflies, as it incorporates many of the taxonomic changes of the last decade or so (for example, splitting off a lot of Paraleptophlebia into Neoleptophlebia, and various changes to the Baetids). It also adds color plates, which are a nice touch, although I think the print medium is inherently very limited in that regard. That's one reason I started this site--so people can see each bug close-up and from many angles.

I've been very impressed by the level of thought that went into producing thorough keys. For example, recent keys (based Jacobus & McCafferty 2008) identify Ephemerella tibialis (formerly Serratella tibialis) nymphs based on some small, subtle features (tiny brown "excresences" on parts of the thorax (Thorax: The thorax is the middle part of an insect's body, in between the abdomen and the head, and to which the legs and wings are attached.) and serrations on the maxillary canine) that are difficult to detect or picture from written descriptions. One of the primary sources includes electron microscope pictures of the excresences, but I don't have any electron microscopes. This book, however, contains pretty good drawings of both features (Fig. 13.85 and 13.90) which weren't found in any of the primary sources I checked, allowing me to make a more confident ID. There are still occasional couplets in the keys for which a better diagram would be helpful, but overall their coverage is really impressive.

It may sometimes be a bit dissatisfying to anglers that they can't identify most mayflies or caddisflies to the species level with this text, only to genus. That's an unfortunate reality of the difficulty of that task; this book wouldn't even fit into a binding if it contained species keys. Anglers wanting to pin an exact species name on their specimens need to either refer to the scientific literature or the angling literature. The keys in the primary scientific literature are often difficult and require looking at tiny features under a microscope with deep knowledge of insect anatomy. Even then, many species aren't fully described. Keys in books for anglers, when available, are a lot easier to follow but tend to be incomplete (especially for western species) and use characteristics that aren't 100 % reliable. For genus-level identifications, this book is as rigorous and up-to-date as anything out there. Some genus identifications can still be frustrating (for example, distinguishing Baetis nymphs from some related Baetidae passes through a couplet describing a "villipore" which is practically impossible to see with amateur equipment). However, that's more a problem for the taxonomists to figure out than for the textbook that compiles all their work. It's just a head-up to the reader that not all genus IDs will be easy, even for well-known genera.

One small inconvenience with this book is that it's almost a victim of outgrowing the printed page. There are so many useful illustrations that they can't all fit on the pages where they're needed, so using the keys means hunting back and forth a few pages at a time almost constantly to reference the relevant figures. I look forward to a time when this information is all available digitally, and not just as a scan of the printed pages, but in a format where illustrations (and perhaps also definitions) always appear where needed.

Another side effect of the book being so comprehensive is that the keys are pretty long and cover everything, so an angler is likely to end up squinting at some odd little insect body parts just to rule out a rare mayfly that only lives on the silty bottoms of large warm rivers 3,000 miles away. The keys become much easier to use once you have some experience, including knowledge of the basic appearance of most of the families and their ranges, to know which taxa to skip over at a glance en route to the real prospects. Roger Rohrbeck's Flyfishing Entomology website has distribution maps that are a very helpful supplement to these keys. Books written primarily for anglers omit these rarities altogether, but that has its own downside, because it's fairly common to find something unusual that isn't in the anglers' books. So it's beneficial to use the full keys, but often enough that you learn which parts to skip and why.

I would highly recommend this edition as an upgrade for those who are or would like to become serious angler-entomologists, especially if your previous edition is the 3rd or earlier, or if you don't have it at all yet. It would not be the right book for somebody completely new to aquatic entomology, unless maybe they have a degree in biology and are looking to dive in deep.

Updates from August 7, 2020

Photos by Troutnut from Valley Creek in Idaho

 From Valley Creek in Idaho.
LocationValley Creek
Date TakenAug 7, 2020
Date AddedAug 16, 2020
CameraCanon EOS 7D Mark II

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