Mayfly – 8 Facts About This Aquatic Insect


An adult mayfly.

Have you ever heard of a mayfly?  Here are some basic facts about this aquatic insect that can be found in rivers and lakes throughout North America and the world.

If you are into fly fishing, like me, then I’m sure you know all about mayflies.  However, for the rest of you I want to give you a little bit of information about this cool bug that you have probably seen around rivers or lakes.  In the middle of winter you generally won’t see them flying around above the water.  But, if you pick up some rocks you may see the larval form of these insects crawling around.  Yes, like many insects, the mayfly undergoes metamorphosis from a larva to an adult.


Bottom photo via Flickr.

8 Mayfly Facts

Mayflies undergo complete metamorphosis.  They begin their life hatching from an egg underwater.  Then they live underwater in their larval stage as a nymph for 2-3 years!  Next they undergo metamorphosis, changing from a nymph to a winged insect.  At this point they rise to the surface of the water, dry their wings and fly off.  Finally, they change into a full adult form, reproduce, and return to the water to lay their eggs.

One cool, little know fact about mayflies is that they are the only bugs to have a stage where they are a winged insect, but not yet a reproductive adult.  This sub adult stage is called, subimago.  Mayflies change from a nymph to this subadult winged stage.  Then within a few hours it changes into a full-grown adult!  Most aquatic insects start out as a larva or nymph, living under water.  They then change into their adult form, emerge from the water, grow wings and fly away.


A mayfly nymph that lives underwater and breathes through gills.

Insects have different strategies to survive the harsh cold winters.  Mayflies survive winters in their nymph form, living on the bottom of rivers or lakes.

As I said above, I enjoy fly fishing.  All stages of the lifecycle of a mayfly are good sources of food for fish, such as trout.  Fly fishers, such as myself, will try to catch trout by using a fly that imitates a mayfly nymph or winged adult.


This adult mayfly has no mouth and only lives a short time. Photo via Flickr.

Adult mayflies have an incredibly short life span.  After they emerge from the water they only live for a few hours or few days.  Basically, when they become an adult their goal is to reproduce.  After they reproduce, the final stage of their life is to return to the water and lay their eggs as they sit on the surface of the water.  While they do this, they only hope that a hungry trout doesn’t see them and eat them up!

Adults do not have mouths, meaning they can’t eat!  On the other hand, the nymphs eat algae under the water.

The nymphs have gills that are used for breathing, just like fish.

Mayflies can only live in clean water and so they are often used to measure the water quality of a stream, river, or lake.  If mayflies can live in an area then the water is clean.

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