Evolution is a gradual, continuous process. It's impossible to fit every type of relationship into the seven well-known taxonomic levels. That's why biologists actually use an even more detailed system:

  • Kingdom
  • Phylum
  • Subphylum
  • Class
  • Subclass
  • Cohort
  • Superorder
  • Order
  • Suborder
  • Infraorder
  • Superfamily
  • Family
  • Subfamily
  • Tribe
  • Genus
  • Subgenus
  • Species
  • Subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.)

(Botanists use a slightly different system for plants.)

Anglers rarely need to refer to any of the these. But in a few cases the distinction between two well-known groups of insects falls into one of the obscure levels. For instance, dragonflies (Anisoptera) and damselflies (Zygoptera) are both suborders of the order Odonata.

For simplicity's sake, the extra levels aren't included on this site. But it can be interesting to investigate them on sites like the USDA's Integrated Taxonomic Information System to learn which well-known insects are more closely related. This may yield interesting surprises. For example, the Isonychiidae mayflies, which have fast-swimming streamlined nymphs, are in the suborder Setisura along with the flat-bodied clinging mayflies of Heptageniidae, so they are more closely related to clingers than to other swimming mayflies like Siphlonurus.

Inconvenient Changes


Even with the sublevels, it's hard to fit everything into its proper place because it's hard to determine the exact evolutionary relationships. That task belongs to an entire branch of biology called phylogenetics, which is constantly making new progress.

As our phylogenetic knowledge grows, the taxonomic hierarchy is adjusted to reflect the new information. This is important to science, but it creates a major headache for anglers trying to keep track of which bugs are which. The Internet has made it easier for entomology-minded anglers to stay on top of the wave of name-changes on well-updated websites like the Mayflies of North America Species List.

There are three common types of changes:

  • Taxa may be moved to different taxonomic levels. For example, Drunella and Attenella and several other former subgenera of Ephemerella were all recently moved up to the level of genus in the same family, Ephemerellidae.

  • Subtaxa may be moved into different taxa. Most often, a species is moved from one genus to another closely related genus. This happens frequently to the prolific little mayflies of the Baetidae family.

  • Taxa are found to be synonyms (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) of other taxa, originally described as different species because a wide degree of individual variation gave their discoverers the wrong impression.


The third type of change is the most common in the mayfly species of importance to fly anglers. Some of the most famous species have been synonymized with others. For example:

  • Ephemerella rotunda is now a synonym (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) of Ephemerella invaria.

  • Baetis vagans is now a synonym (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) of Baetis tricaudatus.

  • Stenonema fuscom is now a synonym (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) of Maccaffertium vicarium.



Sometimes there are differences between the taxa that get synonymized, but they aren't great enough to warrant separate species. In fact, even the precise definition of a species (and just about every other taxonomic level) is a fuzzy area.

While the details of insect classification work themselves out in entomology journals in the decades to come, we anglers can kick back and thank the trout for not reading the Transactions of the American Entomological Society. But we should not give up on keeping our taxa straight, either. When we swap tips about fishing techniques to match each hatch, it's important to use the right names so that our apples are apples and our oranges are oranges.