Ask The Entomologist

Mayflies

True to schedule, the mayflies have returned. Of course, the mayflies didn’t wait for May proper… they’ve been with us for the past month at least.

Here’s the shed skin of one I watched emerging this past week. Note the three tail filaments – this is how you can tell it is a mayfly skin.

It’s hard to get an ID from a cast skin –
I’ll be keeping my eyes peeled for an adult to photograph.

Our pond tends to have the smaller species of mayflies in good abundance – primarily genus Callibaetis. Here are some higher-quality photographs of other mayfly nymphs, so you can get a sense of the variety.

All mayflies belong to Order “Ephemeroptera”, which is Greek for “ephemeral things with wings”. While their winged life-stages may be here today and gone tomorrow, their aquatic young live much longer – a year or more below the surface before taking to the skies.

Mayflies are of an ancient lineage – they were around before creatures with backbones colonized the land. In those early days, the skies were relatively free of predators, far safer than below the water. Far different from the world they inhabit now.

Today, mayflies are a staple food for many creatures – fish, birds, and bats (as well as many insects)… All eat prodigious amounts of mayflies. Fly-fishers are well aware of fish’s dependence on mayflies. Many fly-fishers tend to be insect-watchers, and tailor their flies to match the most abundant mayflies are in their location and season.

We can anticipate our mayflies staying around far longer than the month of May – new adults will emerge all summer long, and can be found well into October, depending on the weather. Their presence can also be used to assess how healthy a body of water is – mayflies don’t do well in polluted areas.

Here’s an adult Callibaetis mayfly that joined me on a walk last fall.
And here’s a writeup on flyfishing to match Callibaetis mayflies’ emergence patterns.

This adult’s size is about right for the shed skin in the top image,
but it’s quite possible that our area contains several species from this genus.

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