Mayflies are arguably the most elegant insect of the fly fishing world.  They vary in size and color and are a staple in the trout’s diet.  As fly fisherman, we imitate this order with patterns like the parachute adams, adams dry fly, pheasant tail, comparadun, and the mercury baetis.

Mayflies offer year round nymphing and dry fly fishing and are located across the world.  Some of the most prolific hatches are mayflies.  I have heard stories of snow plows unburying bridges that were swarmed with mayflies.  Baetis will hatch year round giving mayfly dry flies a necessary place in your box anytime you’re on the water.  In the spring and summer you have dozens of different species that hatch.  If it weren’t for mayflies, entomology would really be rather simple.  Mayflies hatch at all different times of years, the nymphs can look pretty different from species to species and they vary greatly in size.  It’s best to refer to local hatch charts and talk to local fly shops on the rivers you plan to fish to discover what flies are currently hatching, though with this knowledge and a seine, it isn’t necessary as long as your box is stocked.

In this course we will go over many, but not all of the major species of mayflies that are important to anglers.  What’s important to remember is with the knowledge in this course and a way to collect insects under and above the water (fishing seine) you can identify what you need to throw without any knowledge of what you are actually throwing.  You don’t need to know it’s a BWO, you need to know it’s a small olive mayfly with blue/grey wings.  Then match that to what is in your box and present it well for fish catching success.

How to Identify a Mayfly

The key characteristics for a mayfly nymph are 3 tails and single pronged legs.  For emergers and dry flies, the sailboat like wings are the key to identifying it’s a mayfly.  They are delicate, slow flying and beautiful.  When the sunlight hits them, it’s something out of dream.  Though identifying the species from each other can be more of a challenge, mayflies themselves are likely the easiest dry fly to identify.  A spinner (dead dry fly) will often have the wings layed out to the sides on the water.

Mayflies have 2 wings that sit vertical, and have transparency to them and often detailed designs.  the nymphs have long legs, short antennae, and have  3 tails.  Some mayfly nymphs have 2 tails, but you can be certain that a 3-tailed nymph is a mayfly. 

How to Identify Mayflies vs Stoneflies

Mistaking stonefly nymphs for mayfly nymphs is common for anglers.  Here’s the rules to identify the differences:

1- If it has 3 tails, it’s always a mayfly

2- If it has 2 tails, look at the legs.  Mayflies have one hook on their legs while stoneflies have two hooks on their legs.  If the foot doesn’t split into two, then it’s a mayfly.  

Check the tails first, then the legs and you should be able to tell the difference with ease.

As a general rule (not always but often), you will see more prominent and visible antennae on the front of stoneflies and thicker tails.  This can vary of course, but often it is an easy way to ID them as well when you’re trying to figure out if the insect you’re looking at is a stonefly nymph or a mayfly nymph.

Life Cycle of a Mayfly

For the angler, you only need to focus on the nymph, emerger, dry fly and spinner stages to catch fish.  Nymphs and dries are easily identifiable, and you can tell if the fish are eating emergers because when a fish rises to eat an emerger, you will rarely see a mouth and always see a tail.  This is because the emergers and the fish are actually near the surface but oriented down towards the bottom of the river waiting for the mayflies to detach and emerge and then they eat them and swim back down exposing their tail.  Let’s dive into the 4 stages of a mayfly that you need to know to catch more fish.

Mayfly Nymphs

Mayfly nymphs are broken down into 4 groups:  Swimmers, Clingers, Crawlers, and Burrowers.   Common entomology classes will distinguish these 4 types, but the reality is it doesn’t matter much to the angler.  If the goal is to match an identified insect from your seine to a fly in your box, then this knowledge, though interesting, isn’t of much value.  I haven’t heard many anglers say on the river, “Man, those crawler mayflies were way more productive than the burrowers today…”.    If we don’t imitate it as fly fishermen, we don’t really care.  Instead, the way in which it’s fished will determine what the fish are eating.  Most mayfly nymphs are imitated with the same patterns, but fished at different depths and different styles.  Swimmer nymphs for example can be stripped like a streamer to get a strike, burrowers, are often drifted along the bottom.   Identifying which bugs the fish are eating is always a process of elimination.  However, if you use a seine to see what’s in the water and choose the most prevalent insect found, you greatly increase your chance of success. In addition, most mayfly nymph patterns mimic all of these types with moderate accuracy so there isn’t always a need to decipher mayfly behavior patterns.

Common colors and sizes

Colors: Black, white, brown, red, orange, yellow, olive, blue, purple, pink, tan

Sizes: #8, #10, #12, #14, #16, #18, #20, #22, #24, #26

Mayfly nymphs come in all colors and range in sizes #8-#26.  With a range this large, process of elimination or guesswork is difficult and time consuming.  It’s for this reason a seine is so valuable.  A 5 minute seine will show you the color and size of the mayfly nymphs in the water allowing you to match the insects faster and with better accuracy.  Most nymph patterns that have pheasant tails coming out the back imitate mayflies.  Mayfly nymphs, though 3-tailed, when in the water often slicks into one tail.  This is why the pheasant tail fibers work so well for a mayfly nymph imitation.

Pheasant tails, mercury baetis, lightning bug, skinny nelson, and others are great mayfly nymph imitations.  Often sparse, thin patterns with tails and beadheads do the best imitations.