The Mayfly: This James Dean of Insects is Good News for the L.A. River


Throw your hands up in the air and celebrate the thriving mayfly population that keeps our L.A. River nice and healthy. Photo by 


Flickr Creative Commons License


The Los Angeles River may not have the grandeur of east coast rivers, that roar through cities and rambles through verdant greenery, but its waters are still far from the toxic sewer sludge many Angelenos assume it to be.

“We have been monitoring Los Angeles River water quality for years and we can see the trend. The water quality in the river is fairly good,” says Dr. Christopher Solek, senior scientist at the Council for Watershed Health. The council checks whether small invertebrates and fish are able to survive in the water and whether they’re able to reproduce. The answers to these two questions indicate how well the river can support habitat. They’re not testing for drinking quality, clarifies Solek.


In its brief adult life, the mayfly leaves out nonessential activities, like eating, to focus on its true purpose -reproduction. Photo by 

Mark Robinson

Flickr Creative Commons License


For those of us not equipped with fancy scientific equipment or PhDs in biology, Lila Higgins, manager of citizen science at the L.A. County Natural History Museum (NHM) and program coordinator for Play the LA River suggests keeping our eyes peeled for mayflies, or swarms of flying insects over the Los Angeles River.

Though insect swarms conjure images of Biblical plagues, a gathering of mayflies actually means the opposite of death and destruction. “These aquatic insects can be indicators of health,” says Higgins.

Unlike a gathering of flies over rotting food (or over anything really), the presence of a mayfly horde indicates good water quality. The mayflies spend 99 percent of their lives at the river bottom, feeding on algae, decomposing matter, and they need clean water to survive. It may not be pristine, Alpine water, but it’s certainly good enough to support life.

NHM Entomology Curator, Brian Brown says, you could spot mayflies along different parts of the Los Angeles—whether concreted or soft-bottomed. “They’re small and live under rock and algae, so the greenery on the shores is irrelevant,” said Brown.

So, mayflies can live in that little patch of algae at the bottom of a concreted river or that rocky, jagged surface in the Glendale Narrows, but you’re likely to find more kinds of mayflies in greener areas. “You’ll find more types of mayflies in the upper Los Angeles River watershed where the water is colder and cleaner than you would in warmer, more urbanized parts of the river downstream,” said Solek.

But more than a simple way to tell a water source’s cleanliness, the mayfly in itself is an interesting subject of study. Although the word “fly” appears in their names, these insects aren’t really flies. “Mayflies (Ephemeroptera) are their own group of insects,” says Higgins, “Just like there’s a group of butterflies and moths (Lepidoptera), flies (Diptera), and beetles (Coleoptera).

There are more than 3,000 described species that we all call mayflies, “They’re a whole order of insects unto themselves,” said Higgins, “There are just so many of them, people don’t know what they’re about.” Encyclopedia Britannica says many species of mayflies are still waiting to be discovered or described.


Old-school mayfly: Fossil adult Mickoleitia longimanus(



) from the 

Lower Cretaceous

Crato Formation



, c. 108 


. By 

Dr. Günter Bechly

 (Own work), via Wikimedia Commons.

A mayfly lives a fleeting life as an adult. Once they mature, their lives can last as little as a few hours or as long as a couple of days. This is why their order name, Ephemeroptera, comes from the Greek word ephemerosmeaning, “lasting but a day.” Their common name comes from their predisposition to come out in swarms during the summer months, particularly May. Other common names include “shadfly,” “Canadian soldier,” or “fishfly.”

Mayflies have a one-track mind as adults, according to Leslie Mertz of Know Your Insects. As full adults, these insects don’t have functional mouths for eating, their whole purpose is reproduction.

Higgins herself has seen mayflies at dusk along the Glendale Narrows, followed closely by what she thinks are Northern rough-winged swallows, barn swallows, and white throated swifts, swooping into the aerial buffet meal the mayflies represent. “Mayflies are generally very abundant animals. They have a strategy of laying lots and lots of eggs, they just have a massive reproduction cycle. When you do that, you produce a lot of food for other animals like bats, swallows, and swifts,” said Brown.

Their hyper-productive state is good news for Angelenos, who delight in seeing birds on the LA River. These mayflies are one reason why birds can still be spotted along the riverbanks.


Mayfly fishing flies, from Charles and Richard Bowlker's Art of Angling, 1854. 

Wikimedia Commons


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