Entomology Part 3 – Mayflies 101

PC – Brandon Miller Photography

We’ve learned about the three types of flies: Immature, Dry and Streamer in Entomology Part 1.  We’ve also covered the three factors when choosing a fly in Entomology Part 2 – Choosing a Fly.  Now let’s dive into the different bug species, their life cycles and fishing specifics for each species. We’re going to start with the Mayfly Life Cycle.

DISCLAIMER: I am by no mean an expert on this subject, nor do I have a degree in entomology.  This information comes from my personal experiences, countless hours being on the water and even more time spent researching, reading and learning from other anglers.  It’s highly recommended that you take advantage of the many online resources and local classes offered.  This is the “Back to Basics” series with the goal of keeping this information simple and not overwhelming.  With more than 3,000 species of Mayflies things can get a little confusing! We recommend the Entomology Course with The Catch and the Hatch.

United Women on the Fly is happy to announce a collaboration with The Catch and the Hatch to give the UWOTF Community 50% off of their Online, Lifetime Access, Entomology Course.  The course is easy to understand, written for the general angler, has incredible graphics, photos and videos of the different life cycles for each species, fly size and fly recommendation as well as fishing techniques for the different life cycles.  This is an incredible deal!!!  All you have to do is go to   https://thecatchandthehatch.com/uwotf-course-deal/ to purchase your course.  Use the Coupon Code uwotf-course-deal if needed.

Most days you will be graced by the presence of mayflies.  They might be immature or adults ranging from size #8 to #24. I can remember my best day of fishing was floating the Clark Fork River in March during a snow storm with hundreds of fish sipping on Gray Drakes.  Sailboats as far as the eye could see.  Beyond an epic day!!!

Mayflies have 4 different stages in their life.  They are unique as they have two winged adult stages, the Dun and Spinner stage.  As anglers, we fish all four stages of the Mayfly Life Cycle.

Water Temperature

Spring and Fall – Mayfly hatches will start in water temperatures in the low 40s. Peak hatches will occur with water temps of 46° and warmer. Summer mayfly hatches will be seen with water temps in the mid 50s – 60s. 

TIP – Check water temps when fishing.  Pick up rocks and debris in the water.  Do you see any Mayfly Nymphs?  If so, do you see a split near their head?  The split indicates that mayfly nymph is ready to emerge and you might have a good dry fly hatch when the water temps cooperate.

Life Cycles

  • Nymph
  • Emerger
  • Dry (Dun)
  • Spinner


Nymph is the immature stage of a mayfly.  This stage falls into four different categories describing their subsurface behavior. Burrowers, Clingers, Crawlers, or Swimmers.  Depending on the species and environment, mayfly nymphs can spend 3-4 weeks or up to two years under water before they emerge to an adult.  NYMPH CHARACTERISTICS: Two or three tails.


This is the most vulnerable mayfly stage.  When it’s time to emerge, the nymph works its way to the surface.  The nymph will free itself of its shuck into an adult (Dun) resting on the water surface.  The adult mayflies are now in a holding pattern as they are suspended on the water surface “drying off their wings”.  Technically the vulnerable time is the adult mayfly redistributing their bodily fluids into the newly emerged wings.  The opportunistic trout take advantage of this state and feed leisurely.

Think of Clark Kent in his nerdy reporter outfit as he splits open his button down shirt and emerges as Superman.

Adult (DUN)

Adult mayflies (dun) are a favorite food of many fish.  The dull-colored wings stand upright and are nicknamed “Sailboat Wings”.  The lifespan of an adult mayfly is very short, varying with the species.  This could be a few hours up to a couple of days.


The second winged adult stage is the transformation of a Dun to a Spinner.  The clear winged, large eyed mayflies, fly in swarms and mate in the air.  Spinners die shortly after mating, usually within a couple hours.  Spent females tend to be lifeless on the water surface and males tend to fly towards vegetation to live their last hours.

FISHING NOTE – Male and Females can differ in size or color.  Fish the appropriate size fly.  Consider down sizing if needed.


  • Varied Sizes #8-#26
  • Water Temps – 40s – 60s
  • 4 Stages to Mayfly Life Cycle
    • Nymph, Emerger, Adult (Dun), Spinner
  • Nymphs – Most Common Have Three Tails
  • Vulnerable State During Emerger Stage
  • Adult have a Sailboat Wing
  • Spinner Lifecycle Happens in the Evening

UP NEXT – Entomology Part #4 – Mayflies 101 Continued…

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