Why Emergers?

Updated: Sep 23, 2019

Why emerger patterns are so effective

I discovered how well emergers work pretty much by accident. I recall a trip in which several fish were rising, but we couldn’t see the bugs they were feeding on. We were left to our best guesses on pattern selection. I started off with a standard of mine, a size 16 quill bodied thorax dun. This is a high riding pattern that doesn’t imitate any specific species, but is representative of a fully developed generic mayfly adult. My fishing partner tied on one of his go to’s, a size 16 elk haired caddis, another high riding fly. After several frustrating attempts at rising trout, I decided to do what most fly fishermen do and change things up. I pulled out a new pattern to me at the time, the Klinkhammer. What made me choose this pattern? I’m not quite sure but I’m guessing it probably had to do with the fact that I had recently tied a few for the first time and thought they looked and sounded cool. I had hook ups on my next 3 casts. My partner switched up to a parachute style fly with similar results.

Two of our favorite emerger patterns. The Hare's Ear Parachute, and the Klinkhammer.

I want to make one thing clear. I’m in the camp that believes when dry fly fishing (other than during a specific concentrated hatch), quality of presentation FAR outweighs fly selection. But when you know your getting quality drag free drifts and the trout still aren’t showing interest, something needs to change.

Why did changing from one pattern to another make such a difference for us? All four patterns I mentioned above typically fall into the “dry fly” category. Well, while all of these patterns may look similar to fly fishermen who view flies from above the water, they look totally different from a trout’s perspective which is obviously below the water. Why does this matter to a trout?

Now I’m not a trout dietitian, but I think we can all agree that the bigger the bug, the more calories it will provide. I think this is the reason that some fly fisherman believe that trout feed on the largest possible food source that’s available to them at the time. If this were the case, maybe we should have thrown on size 10 stimulators. Would that have done the trick? Maybe. We were having so much success with what we had tied on that we didn’t even try. (That, and the fact that I don’t carry anything larger than a size 14 dry fly other than a few terrestrial patterns.)

My observations:

I on the other hand, believe that trout make their menu selections based upon calories their food provides (x) minus the number of calories it takes for them to “capture” their prey (y). I am not inclined to research the difference in calories between various insects, so to demonstrate this, I’m going to use a simplified example. Hang with me here, I promise there won’t be a math quiz at the end.


Calories bug provides (x) = 10

Calories burned to capture bug (y) = 6

Then 10 - 6, the trout is net positive 4 calories.

Trout menu options:

(Remember, I’m not using exact calories here, just showing hypotheticals to explain my point of view).

Option 1.

Fully emerged “big bug” adult dun

Calories provided: 15

Calories needed to capture: 11

Net calories for the trout: 4

Option 2.

Smaller bug in the emergence stage

Calories provided: 9

Calories needed to capture: 2

Net calories for the trout: 7


“Have you had a chance to look over the menu?”


“Um yes sir, I’ll have the #2, extra crispy, light on the trailing shuck please.”

High Riding Dry Fly

Emergers almost always have a lower “calories needed to capture” value because unlike fully emerged duns that fly away quickly after getting through the surface film and drying their wings, emergers spend significantly more time fighting their way through the surface film. So our equation holds even more true if both the full adult dun and the emerger provide the trout with the same amount of calories.

Adult dun on top of the water

Calories provided: 9

Calories needed to capture: 7

Net calories for the trout: 2

Emerger fighting through the film

Calories provided: 9

Calories needed to capture: 4

Net calories for the trout: 5

Add to all of this, that because they spend so little time on the water after emergence, adult duns have a much higher likelihood of providing the trout with 0 calories than does an emerger which becomes a “sit down meal” while they are fighting through the film. If you were at a buffet and the food on the islands were on a conveyor belt, would you chose the food that is on the faster or slower one?

*Side note, there are a few species of flies that spend a significant amount of time riding on top of the water after emerging into full adults. This is the exception instead of the rule, and breaking down which flies these are is not the intent of this article.

I don’t think trout take the time to read the food labels of flies to determine their serving size and caloric makeup. I believe that through natural selection and years of genetic improvements, the trout who figure this out are the ones who survive. Remember, fly selection for fly fisherman is interesting and fun. Selecting which menu option for a trout is a life or death decision that if they get wrong too often, they wouldn’t be around for us to chase.

Noses Up!

  • Twitter