Minnesota Mayflies

Order Ephemeroptera

Ephemeroptera is the order of small to medium-sized flying insects known as mayflies. They have elongated, very soft bodies. The forewings are triangular, very large, and have many veins. They are held together above the body when at rest. The hindwings are small and round, or in some species missing. The abdomen has 2 or 3 hair-like tails. The antennae are short, bristle-like, and inconspicuous. The last part of the leg (tarsus), corresponding to the foot, has 3 or 5 segments. The mouthparts are small, poorly developed, and non-functional. Adults often emerge in large numbers, sometimes piling up on the shore. Many species engage in swarming flights, where they fly up and down in unison. They do not feed and seldom live more than 1 or 2 days.

The young, called nymphs, are aquatic. They have leaf-like gills along the sides of the abdomen, and 3 hair-like tails at the end of the abdomen. Most mayfly nymphs develop in streams and rivers, some develop in lakes and ponds. The feed on small aquatic organisms and organic debris. They swim to the water surface or crawl onto emergent vegetation or rocks to complete the second-to-last molt. This subadult stage has functional wings and is called a subimago. They fly to nearby vegetation and molt one last time, emerging as adults. Mayflies are unique as the only insect that molts again after developing functional wings.

Mayflies are an important food source for freshwater fish. Fly fisherpersons use mayflies as bait.

There are more than 3,000 species in more than 400 genera in 42 families of mayflies worldwide. There are 611 species in 59 genera in 21 families in North America north of Mexico. There are estimated to be 100 to 119 species in Minnesota.

giant mayfly
Photo by Luciearl
Recent Additions

Giant mayfly


Giant mayfly (Hexagenia limbata) is a large “common burrower” mayfly. It is very widespread, occurring in the United States and southern Canada from the east coast to the Great Plains and on the west coast. It is mostly absent from the desert and mountain regions in the west. It is the most common mayfly in the Midwest, and is common in Minnesota.

Larvae are found in organic, silty or mucky bottoms of lakes, ponds, and rivers, usually about three meters below the water surface. They feed on organic material suspended in the water. Immature adults are found on trees and bushes on shores near the bodies of water from which they emerged. Adults are found flying in swarms over land near the water body. They do not feed and live from just a few hours to a few days. Emergences are synchronized and can produce swarms so large that they can bee seen by weather satellites. Snow plows are sometimes used to clear dead mayflies off of roads.

Giant mayfly is said to be the largest mayfly in the United States. It can be more than one inch in length, not including two hair-like “tails” that can be equally long. The body may be yellow, yellowish-brown, brown, or even white. Aside from its very large size, giant mayfly is identified by the wing veination, and by the four-segmented end part (tarsus) of the hind leg.

  giant mayfly  
    Photo by Luciearl  

Pond olive


Pond olive (Cloeon dipterum) is a small minnow mayfly. It occurs throughout Europe, where it is native, and in Asia and North America, where it has been introduced. The earliest North American record is from Illinois in 1953. It is now widespread across the continent. In the United States it is currently mostly restricted to the northeast and to Washington state. It is rare in Minnesota. Nymphs are found mostly in ponds, but also in the shallow margins of lakes and in slow areas of rivers and streams. They feed on algae, small aquatic organisms, and organic debris. Adults are found on vegetation near ponds. They do not feed and seldom live more than 1 or 2 days.

Adults are reddish-brown and have 2 very long hair-like tails at the end of the abdomen. The compound eyes on the female are on the sides of the head. On the male the compound eyes have additional large, orange, turban-like parts that meet at the top of the head. These adaptations are said to allow the male to isolate in a swarm females that are not yet paired with another male. Some authors say that pond olives have no hindwings. Carl Linnaeus in 1761 described the hindwings as “hardly present.”

  pond olive  
    Photo by Alfredo Colon  
Other Recent Additions







This list includes only mayflies that have been recorded in Minnesota, but not all of the mayflies found in Minnesota.

Profile Photo Video    

Aphrodite’s flat-headed mayfly (Leucrocuta aphrodite)


a small minnow mayfly (Paracloeodes minutus)


big river small minnow mayfly (Pseudocloeon longipalpus)


brown drake (Ephemera simulans)


brown small minnow mayfly (Baetis brunneicolor)


brush-legged mayfly (Isonychia velma)


cloudy prong-gilled mayfly (Leptophlebia nebulosa)


common small minnow mayfly (Baetis tricaudatus)


common small square-gilled mayfly (Caenis latipennis)


common spiny-headed burrowing mayfly (Pentagenia vittigera)


confused small minnow mayfly (Acentrella turbida)


dark cahill (Stenonema femoratum)


Dark Hendrickson (Ephemerella subvaria)


early brown spinner (Leptophlebia cupida)


emergent mayfly (Hexagenia bilineata)


filtering small square-gilled mayfly (Amercaenis ridens)


fragile prong-gilled mayfly (Paraleptophlebia debilis)

Profile Photo Video  

giant mayfly (Hexagenia limbata)


glassy flat-headed mayfly (Epeorus vitreus)


golden drake (Anthopotamus distinctus)


Hebe’s flat-headed mayfly (Leucrocuta hebe)


lake hex (Hexagenia atrocaudata)


Laprairie small minnow mayfly (Labiobaetis frondalis)


Laurentian armored mayfly (Baetisca laurentina)


little black spiny crawler mayfly (Teloganopsis deficiens)


maculated small square-gilled mayfly (Sparbarus maculatus)


mahogany dun (Isonychia bicolor)


Manitoba small minnow mayfly (Labiobaetis dardanus)


march flat-headed mayfly (Maccaffertium vicarium)


meager flat-headed mayfly (Maccaffertium exiguum)


Minnetonka flat-headed mayfly (Stenacron minnetonka)


modest flat-headed mayfly (Maccaffertium modestum)


northern small square-gilled mayfly (Caenis diminuta)


northern summer mayfly (Siphlonurus alternatus)


orange cahill (Stenacron interpunctatum)

Profile Photo Video   pond olive (Cloeon dipterum)

pretty flat-headed mayfly (Maccaffertium pulchellum)


pretty small minnow mayfly (Callibaetis pretiosus)


red speckled dun (Callibaetis ferrugineus ferrugineus)


ringed small minnow mayfly (Acentrella parvula)


Rock Island small minnow mayfly (Labiobaetis propinquus)


Say’s small square-gilled mayfly (Caenis hilaris)


small mayfly (Pseudocloeon propinquum)


small minnow mayfly (Acentrella rallatoma)


small square-gilled mayfly (Cercobrachys etowah)


southern flat-headed mayfly (Maccaffertium mexicanum)


stream mayfly (Nixe kennedyi)


tardy small square-gilled mayfly (Caenis tardata)


terminal flat-headed mayfly (Maccaffertium terminatum)


tiny blue winged olive (Acerpenna pygmaea)


Walker’s tusked sprawler (Anthopotamus verticis)


Walsh’s hackle-gilled burrowing mayfly (Anthopotamus myops)


white fly (Ephoron leukon)


white fly (Ephoron leukon)


yellow-streaked small minnow mayfly (Baetis flavistriga)


Young’s small square-gilled mayfly (Caenis youngi)


Acentrella parvula (ringed small minnow mayfly)

Acentrella rallatoma (small minnow mayfly)

Acentrella turbida (confused small minnow mayfly)

Acerpenna pygmaea (tiny blue winged olive)

Amercaenis ridens (filtering small square-gilled mayfly)

Anthopotamus distinctus (golden drake)

Anthopotamus myops (Walsh’s hackle-gilled burrowing mayfly)

Anthopotamus verticis (Walker’s tusked sprawler)

Baetis brunneicolor (brown small minnow mayfly)

Baetis flavistriga (yellow-streaked small minnow mayfly)

Baetis tricaudatus (common small minnow mayfly)

Baetisca laurentina (Laurentian armored mayfly)

Caenis diminuta (northern small square-gilled mayfly)

Caenis hilaris (Say’s small square-gilled mayfly)

Caenis latipennis (common small square-gilled mayfly)

Caenis tardata (tardy small square-gilled mayfly)

Caenis youngi (Young’s small square-gilled mayfly)

Callibaetis ferrugineus ferrugineus (red speckled dun)

Callibaetis pretiosus (pretty small minnow mayfly)

Cercobrachys etowah (small square-gilled mayfly)

Cloeon dipterum (pond olive)

Epeorus vitreus (glassy flat-headed mayfly)

Ephemera simulans (brown drake)

Ephemerella subvaria (Dark Hendrickson)

Ephoron album (white fly)

Ephoron leukon (white fly)

Hexagenia atrocaudata (lake hex)

Hexagenia bilineata (emergent mayfly)

Hexagenia limbata (giant mayfly)

Isonychia bicolor (mahogany dun)

Isonychia velma (brush-legged mayfly)

Labiobaetis dardanus (Manitoba small minnow mayfly)

Labiobaetis frondalis (Laprairie small minnow mayfly)

Labiobaetis propinquus (Rock Island small minnow mayfly)

Leptophlebia cupida (early brown spinner)

Leptophlebia nebulosa (cloudy prong-gilled mayfly)

Leucrocuta aphrodite (Aphrodite’s flat-headed mayfly)

Leucrocuta hebe (Hebe’s flat-headed mayfly)

Maccaffertium exiguum (meager flat-headed mayfly)

Maccaffertium mexicanum (southern flat-headed mayfly)

Maccaffertium modestum (modest flat-headed mayfly)

Maccaffertium pulchellum (pretty flat-headed mayfly)

Maccaffertium terminatum (terminal flat-headed mayfly)

Maccaffertium vicarium (march flat-headed mayfly)

Nixe kennedyi (stream mayfly)

Paracloeodes minutus (a small minnow mayfly)

Paraleptophlebia debilis (fragile prong-gilled mayfly)

Pentagenia vittigera (common spiny-headed burrowing mayfly)

Pseudocloeon longipalpus (big river small minnow mayfly)

Pseudocloeon propinquum (small mayfly)

Siphlonurus alternatus (northern summer mayfly)

Sparbarus maculatus (maculated small square-gilled mayfly)

Stenacron interpunctatum (orange cahill)

Stenacron minnetonka (Minnetonka flat-headed mayfly)

Stenonema femoratum (dark cahill)

Teloganopsis deficiens (little black spiny crawler mayfly)


























giant mayfly




















pond olive


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Created 11/5/2020

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