Mayflies of North America

By Donny Benkendorf (@benkedonny on instagram)

There are 23 mayfly families in North America. However, just 3 of these mayfly families contain over half of all the mayfly species and are by far the most commonly encountered on trout streams! These 3 families are Baetidae (the small minnow mayflies), Ephemerellidae (the spiny crawler mayflies), and Heptageniidae (the flat-headed mayflies).

As a quick taxonomy refresher, mayfly (or Ephemeroptera, which means short-lived wing in Latin) is a taxonomic order.

1. Within each order there are several families – for example, Baetidae is one family within Ephemeroptera. All family names end in ‘dae’.
2. Within each family there are several genera – for example, Baetis is one genus within the family Baetidae.
3. Within each genus there are several species – for example, tricaudatus is a species within the genus Baetis and the full species name is written Baetis tricaudatus. The genus and species names are always italicized.

NOTE: All of the photos in this article were provided by fellow aquatic insect enthusiast Bob Hendricks (@buddhabob2hanlubo)!

Baetidae (the small minnow mayflies)

Species in Baetidae are called minnow mayflies because the nymphs swim by undulating their bodies and they do look a lot like small minnows when they swim. Most of their time in streams and rivers is spent underneath rocks or among submerged vegetation in moderate currents. The adults are commonly called blue winged olives (or BWOs), but they can be several different colors ranging from more brown to more grey depending on the stage (dun or spinner) and depending on the species. There are 28 genera (genera is plural, genus is singular) within Baetidae.

Ephemerellidae (the spiny crawler mayflies)

The spiny crawlers are so named because they have a scraggly, almost clumsy appearance and spiny legs that are good at clutching onto submerged structure. They generally inhabit the underside of submerged stones in moderate currents. There are 14 genera within Ephemerellidae. Two of the most well-known genera are Ephemerella (which are often called pale morning duns or PMDs) and Drunella (which are often called the western drakes).

Heptageniidae (the flat-headed mayflies)

The flat-headed mayflies have very flattened, streamlined bodies that allow them to live in the swiftest currents where they masterfully cling to submerged stones and graze the fine layer of microbes and algae that grow there. In the fly fishing literature, the family is also often called the clinger mayflies. There are 16 genera within this family.