What is an Emerger Fly Pattern? An Illustrated Guide

Updated: Oct 19

Klinkhammer Emerger fly fishing pattern

Emerger fly patterns are used to imitate the time period in an aquatic insect’s life when it leaves its home on the stream bed and ascends to the surface to spread its wings and take flight as an adult. These patterns are fished on or in the surface film without added weight to the fly or leader. The materials used to tie emerger fly patterns are based upon the type of insect the angler is attempting to imitate.

In this guide we will cover:

What is an emerging aquatic insect?

An emerger isn’t technically a stage of an aquatic insect’s life cycle. It refers to an aquatic insect that's ascending up the water column to transform from its nymph or larva life cycle stage, to its subimago or adult stage.

There are two types of emerging aquatic insects that are of most importance to trout fisherman.

Mayfly Emergers

Mayflies spend the vast majority of their lives underwater. After hatching from an egg, a mayfly enters into its nymph stage. Nymphs have six legs, an exoskeleton shell, and are between 3mm and 35mm in length, depending upon species. Their early lives are spent crawling on underwater rocks and weeds to find algae and other vegetation to eat. At some point, weather conditions, barometric pressure, and other unforeseen natural forces signal to them that it’s time to move to the next stage of their lives. When this occurs, their bodies fill with air and they begin their vertical ascent toward the surface where they will become winged adults. During this ascent they struggle to escape from their exoskeleton skin and untuck their wings in preparation for taking flight once on the water’s surface.

Caddis fly Emergers

After hatching from their eggs, caddisflies enter their larva stage and appear as small grub-like worms. They have short legs located at their thorax, a tapered body that they “wiggle” to swim upside down, and range between 1 mm to 30 mm in length depending upon species. They spend their early lives crawling on steam bed rocks and “drifting” in the underwater currents. After about 30 weeks, a caddis moves into its pupa stage and dwells in a case that it builds around itself. At this point, it has developed wings that are tucked against its body, and within a few weeks it chews its way through the case to begin its ascent to the surface. During this ascent, they struggle to get to the surface where they will attempt to spread their wings away from their body and dry them off so they can take flight.

Why are Emerger Fly Patterns are Effective?

Trout quickly learn to consume more calories than they burn. Throughout their lives they see several “”opportunities” for food and learn some meals require less work than others. After struggling up the water column, emergers often become exhausted and get stuck in the surface film while trying to unfold their wings and fly away. Becoming “stuck” in the surface film and unable to swim away makes them “sitting ducks” for rising trout. (It would be like us trying to take off a waterlogged sweatshirt while at the same time trying to run away from a lion.) Emergers require less work and fewer calories burned for a trout to catch than would a fully winged moving target.

I’m not a trout dietitian, but I think we can all agree that the bigger the bug, the more calories it will provide. This is the reason some fly fisherman believe trout feed on the largest food source available to them at the time. If this were the case, maybe we should always tie on size 10 simulators?

Not exactly. Oftentimes trout prefer an emerger of a smaller insect stuck in the film over a larger one moving on the water’s surface.

Trout prefer emergers for 3 reasons:

  1. If an insect is fully emerged and moving on the water’s surface, a trout may have to expend more energy to capture its prey than it actually gains in calories from the meal.

  2. Emergers stuck in the film are exhausted and have limited fleeing capabilities. This significantly reduces the possibility a trout would “miss” its target at the time of attack.

  3. Trout see objects in the film and below the surface much better than they do above it. This clarity of vision gives them confidence in their choice of meal.

Types of Emerger Fly Patterns