Mayflies are an important source of food for fish

Elvis Elvis

Mayflies can not be overlooked or misunderstood. The knowledge of this insect can literally mean the difference between a successful day fishing or a miserable disappointment!

In order to fully understand the aquatic world you need to have a basic understanding of the mayflies life cycle and what types are present in your area.

Don’t worry…you don’t have to become an Entomologist (Bug Guy) anymore than you need to become a computer programmer to run your computer!

These insects account for a large portion of a trout’s diet. Being able to recognize a mayfly hatch as it is developing is the key. Many times the fish will be feeding on this insect before it fully reaches it’s adult stage. Let’s take a closer look at the lifecycle of the mayfly. The mayfly is referred to as an incomplete metamorphosis meaning that there is no pupal stage.

  • Egg
  • Larvae or Nymph
  • Adult


The female lays her eggs by either flying over the water, dipping her abdomen into the water, on a rock, or sometimes they even submerge themselves to find a suitable place to deposit their eggs. It has been said that they can lay anywhere from a few hundred to thousands of eggs, some all at once…others a few at a time. These eggs may hatch immediately or may take up to a full year to reach the correct tempature and day length.


As the egg hatches, depending on what type of insect it is, it becomes either a burrowing, swimming or crawling nymph. As you can see, if you know what type of mayflies are present in your area (info that is easily obtained from a local fly shop or state website) you can do a little research and determine what type of nymph it will hatch into.

Mayflies are an important source of food for fish

To the fly fisher, this is very important in offering a nymph that is similar to those present in the stream, and what type of presentation is required. A crawling nymph may be fished dead drift but you wouldn’t want to dead drift a swimmer. Starting to get my drift?

Nymphs feed on many different types of food. Some are predators feeding on Chironomids and others feed on algae and decaying plants. As they mature and grow these nymphs molt (shed their skins) and start making their way to the surface. Some molt on the bottom and swim to the surface while others molt on their way to the surface and some hatch on the surface.


Once on the surface or in the surface film the dun will sit there waiting for their wings to dry so they can fly. This is the subimago stage (non-fertile) and is considered by many to be their most vulnerable time. During this time their wings appear dull. After a few hours or several days they once again molt into the Imago (fertile adult spinner) stage where they have longer legs, tails and have shiny wings.

If you have spent any time on the water you know exactly what I am talking about. The mating is conducted in a big swarm with the male dipping up and down until he attracts a mate. Once the mating is complete the female deposits her eggs as stated above.

After the mating and egg laying are completed the mayfly dies and usually falls into the water as a spinner.

Again, recognizing a spinner fall and having a suitable fly to offer can really spice up your fly fishing! Every dry fly box should have a few spinner imitations just for these occasions.

One of my old timer friends even goes as far as to bend the hook shank while it is still in the vise to help with the presentation of a dead or crippled spinner.

While I was fishing the Lower Owens River in California I experienced a small Blue Winged Olive (BWO) hatch starting to take place around mid-morning. My fishing partner and I had tried throwing everything but the kitchen sink at them with no luck until the hatch started.

We quickly tied on a size 22 BWO with a size 24 Yong special as a dropper. During the next few hours I must have caught over 45 fish, mostly wild Browns, totally making that trip one that I will never forget.