Insect Identification

*** Note: KnowYourInsects.org does its best to include correct identifications of insect photos. It’s always possible that we made a mistake, however, so if you see a misidentification, please contact us and we will correct it. Thanks!

Order Ephemeroptera: the mayflies — Examples
For more information, see the article: “How to Survive a Massive Mayfly Swarm” on the Entomological Society of America’s blog Entomology Today.

Families represented below:

Baetidae

Ephemeridae, the common burrower mayflies

Hexagenia limbata (no specific common name), family Ephemeridae.
□ This photo of an adult Hexagenia limbata shows a row of small square cells on the leading edge of the forewing, as well as the many square cells on the rest of its wings.
□ Adult mayflies have neither functioning mouthparts nor digestive systems, but that is OK, because they only live a day or so — long enough to mate and lay eggs. The adult Hexagenia limbata may reach more than an inch (2.5 cm) in body length, with cerci (the “tails”) stretching back another inch or more.
Photographed by: Tyson Yarborough. Identified by: KnowYourInsects.org/. Location: Kerrville, Texas, USA. Date: 21 May, 2023.

Hexagenia bilineata (no specific common name), family Ephemeridae.
□ Notice the brown stripe on the head and the brown marking on its front femur (“thigh”). These are characteristic features of Hexagenia bilineata. A similar-looking species is Hexagenia limbata, which is about twice the size (a body length up to inches or 3 cm) and swarms in the spring, vs. Hexagenia bilineata, which is about three-quarters of an inch or 1.8 cm, and appears in mid-summer in Kansas where this photo was taken.
□ This may be a subimago, also called a dun, which is the unique developmental stage in mayflies that has wings but it not yet a reproductively mature adult. See the photographer’s comment below.
Photographed and identified as a mayfly by: Lauryn Filby. Location: De Soto, Kansas, USA. Date: 8 July 2016.
Lauryn says, “This specimen lacks significantly dark characteristics. It may be younger which would cause a lack of pigmentation.”

Anglers abbreviate the giant mayfly’s scientific name of Hexagenia limbata to simply Hex. This species typically emerges from the water en masse in the spring. This so-called “hex hatch” causes the fish to go into a feeding frenzy, which can make for some excellent fishing.

The Ephemeridae family are known as burrower mayflies because the nymphs runnel into the underwater substrate and live there.

Mayfly, possibly a giant mayfly in the genus Hexagenia, family Ephemeridae.
□ In more temperate areas of the United States, many species of giant mayflies become adults altogether and engage in a short-lived mating spree before dying. In warm climates, such as Louisiana where this one was spotted, adults may emerge almost year-round. This one was photographed in late August.
□ This is a typical posture of mayflies: the forelegs are held forward so they look almost like antennae.
Photographed and identified by: Jennifer Green. Location: New Iberia, Louisiana, USA. Date: 28 August, 2021.
Jennifer found this one “hanging from our ceiling fan chain.”

Mayfly, possibly a giant mayfly in the genus Hexagenia, family Ephemeridae.
□ This swarm of mayflies hatched altogether in early July in Tennessee. The photographer described “groups of thousands.” A feature of the giant mayflies (in the genus Hexagenia) is a thin, dark border on the hind wing, as seen here, although not all individuals exhibit the border.
Photographed by: Youssef Eryan. Identified by: KnowYourInsects.org. Location: Nashville, Tennessee, USA. Date: 13 July, 2020.

Green drake, Ephemera danica, family Ephemeridae.
□ This large green drake has a body about an inch (2.5 cm) long, and tails that can extend another 2 inches (5 cm).
□ As a naiad (immature), this insect lives in at the bottom of clean lakes, and fast-moving rivers and streams. The similar and closely related species Ephemera vulgata has naiads that live in still water, such as stagnant ponds, and can survive even in polluted water.
Photographed and identified to order by: Ellie Russell. Identified to species by: KnowYourInsects.org. Location: Lough Derg, Ireland. Date: 3 June, 2021.
Ellie says, “We saw this fly on our car today beside Lough Derg looking out at Holy Island.”

Burrower mayfly, family Ephemeridae.
□ This photo of the underside of burrower mayfly shows its forelegs stretched forward and its other four legs out to the sides, which is a typical pose for mayflies. Notice also the tiny segments in the two long and filamentous cerci The cerci are also known as caudal filaments.
Photographed by: Nicky Schauder. Check out the Schauders’ Permaculture Gardens program. Identified to species by: KnowYourInsects.org. Location: Erie, Pennsylvania, USA. Date: 17 June, 2023.
Nicky says she and her family “saw this little critter hanging out on our windy window.”

Polymitarcyidae, the pale burrowers

Pale burrower, Ephoron virgo, family Polymitarcyidae.
□ Pale burrower is an apt name for this mayfly. With its light-tan coloration, it is definitely pale, and the aquatic larva is a burrower in that it digs a tunnel in the substrate underwater. The larva lives in the tunnel, using its gills to fan water past. This fanning motion also brings in prey (smaller invertebrates).
Photographed by: Ingmar Janssen. Identified by: KnowYourInsects.org. Location: The Netherlands. Date: 20 July, 2018.

Most of a mayfly’s life is spent underwater as a youngster (naiad). Most naiads eat algae and vegetation, although a few species will eat other little critters in their freshwater environment.

Heptageniidae, the flatheaded mayflies

Flat-Headed Mayfly, Heptagenia culacantha

Heptagenia culacantha (no specific common name), family Heptageniidae.
□ First discovered in 1985, Heptagenia culacantha is a rare and quite beautiful mayfly. It is found in a small area of New York and Pennsylvania. This species and others in this family (Heptageniidae) are collectively known as flatheaded mayflies. Compared to other mayfly families, flatheaded mayflies have naiads (aquatic immatures) with flatter bodies — they almost look as if they have been stepped on — and their eyes are on top of the head rather than on the sides.
□ It is a large mayfly with a body length of about nearly an inch (about 2 cm), and that is not counting the long caudal filaments (the “tails.”
Photographed by: Sam Decker. Identified by: Tony Ertola. Location: Delaware River near Long Eddy, New York, USA. Date: June, 2020.

Heptagenia culacantha, subimago, family Heptageniidae.
□ This is the subimago of Heptagenia culacantha. Subimago means that it is in the stage just before it will become a reproductively capable adult. Anglers often call the subimago a “dun.” Mayflies are unusual among the insects in having a non-adult that is capable of flight.
Photographed and identified by: Tony Ertola. Great find and identification, Tony! Location: Delaware River near Long Eddy, New York, USA. Date: June, 2016.
Tony says, “I wish the pic was clearer.” KnowYourInsects.org says, “We are just thrilled you got a photo at all, Tony!”

Mayfly naiads (immatures) have gills not behind the mouth as fish do, but skirting the outside of the abdomen. Usually the gills are rounded, but some species, such light cahill mayflies, have gills that are pointed.

Light cahill mayfly, quite possibly Stenacron interpunctatum, female, family Heptageniidae.
□ The dark veins at the top of each forewing of this light cahill mayfly show up nicely, along with a single elongated dark spot. This mayfly is common along streams in the Upper Midwest of the United States.
Photographed and identified by: Milo Smith. Nicely done, Milo! Location: Williamstown, Ontario, Canada. Date: 5 July, 2022.

Flatheaded mayfly, possibly in the genus Stenacron, family Heptageniidae.
□ This flatheaded mayfly has huge eyes and very long caudal/tail filaments.
Photographed by: Denise Rulason. Identified by: KnowYourInsects.org. Location: Interlochen, Michigan, USA. Date: 24 June, 2018.

Baetidae, the small minnow mayflies

Small minnow mayfly (Baetis flavistriga)

Baetis flavistriga (no specific common name), subfamily Baetinae, family Baetidae.
□ As an adult, this species of small minnow mayfly known by the scientific name of Baetis flavistriga reaches a body length of about 6-7 mm (0.2-0.3 inches), not including the tail filaments. The alternating dark-light-dark sections on its body are characteristic of this species.
Photographed by: Marv Goldberg. Identified by: KnowYourInsects.org. Location: Tamarac, Florida, USA. Date: 2 June, 2023.

Pond olive, female, Cloeon dipterum, subfamily Cloeoninae, family Baetidae.
□ This pond olive is a small mayfly that is sexually dimorphic: the female (shown here) looks different from the male. The female has brown shading along the edge of her forewings, while the male has clear forewings. In addition, the male has a second pair eyes, one pair stacked on top of the other. This second “superpositioned” pair look rather like brown hamburger buns. To see the male, click here (BugGuide).
Photographed and identified as a mayfly by: Diana Luntena. Identified to species by: KnowYourInsects.org. Location: Riga, Latvia. Date: 3 September, 2023.
Diana says, “I only noticed it because of the long tails it has. Otherwise quite small, almost unnoticeable.”

A small minnow mayfly in the genus Callibaetis, subimago, family Baetidae.
□ This species of small minnow mayfly is definitely small — this one is perched at the bottom of the photographer’s thumb. In most mayflies, females mate and start laying eggs almost immediately with the eggs hatching a few days later. Females in the genus Callibaetis, however, retain their eggs until they mature, so when she lays them, they hatch almost immediately.
□ The photographer saw these mayflies emerging from the water. Anglers often call them speckled duns.
Photographed and identified to family by: John Cary. Nice job, John! Identified to genus by: KnowYourInsects.org. Location: near Pinecrest, California, USA. Date: 4 August, 2021.
John spotted this species while fly fishing in Emigrant Wilderness, “on the outlet of Kennedy Lake at an elevation of 8000 feet (2400 meters).”

Small spurwing, adult, Centroptilum luteolum, family Baetidae.
□ This small spurwing has a dark thorax, big eyes and a dark end on its abdomen.
Photographed and identified to order by: Simon Adams. Identified to species by: KnowYourInsects.org. Location: Colchester, England. Date: 4 June 2014.

Unidentified small minnow mayfly in the family Baetidae.
□ Small minnow mayflies may have two or three caudal/tail filaments, depending on the species. The caudal filaments comprise two cerci, and sometimes a central filament. The caudal filaments are quite fragile, and can easily break off (as is the case here).
Photographed by: Hannah Doviak. Nice job, John! Identified by: KnowYourInsects.org. Location: Federal Way, Washington, USA. Date: 9 September, 2021.
Hannah says, “This was on my window and is tiny (no bigger than my thumbnail).”

Unidentified small minnow mayfly in the family Baetidae.
□ This appears to be a small minnow mayfly in the family Baetidae, which was found in India.
□ Note: A new species of minnow mayfly in the Baetidae family was discovered recently in India — just 4-5 mm (0.16-0.19 inches) in body length and with only one pair of wings rather than the typical two pairs. To read about this new species (Labiobaetis soldani) click here (ScienceDaily).
Photographed and identified to order by: Dr. Somashekhara Achar. Identified to family by: KnowYourInsects.org. Location: Tumkur, Southern Karnataka, India. Date: 22 February, 2020.

Additional unidentified mayflies

A swarm of unidentified mayflies.
□ The little white specks in this photo are all mayflies — a big swarm on this bridge in Indonesia! As seen, mayflies are attracted to lights at night. See the next photo for a close-up of one individual from this swarm.
Photographed by: Galuh Prasetyawan. Identified by: KnowYourInsects.org. Location: Indonesia. Date: 25 January 2017.
Galuh says the mayflies swarmed at dusk, caused slippery driving conditions when they landed on the road surface, and “a lot of motorcycles fell.”

Unidentified mayfly.
□ This is a closeup of a mayfly from the swarm shown in the previous photo. This photo shows the underside of the mayfly.
Photographed by: Galuh Prasetyawan. Location: Indonesia. Identified by: KnowYourInsects.org. Date: 25 January 2017.

Mayfly, family unidentified.
□ Nearly all mayfly species have two pairs of wings: one large front pair (the forewings), and one much-smaller pair (the hindwings). When resting (not flying), mayflies usually hold their wings folded, which can make it difficult to see the hind wings.
Photographed and identified by: Dayana Gonzalez-Saez. Location: Connecticut, USA. Date: 25 May, 2017.

Fly fishermen often call mayfly naiads (immatures) “drakes”. The term comes from England, which is where fly fishing originated, and refers to mayfly-mimicking lures, which often are decorated with feathers from a male duck. Male ducks are called drakes. Somewhere along the line, the fishermen started calling naiads drakes, too.

Unidentified mayfly, adult and exuviae (shed casing).
□ The one on the left is an adult mayfly that may have hatched out of the casing (or exuviae) on the right. With these insects, the young (naiads) live underwater for many months. When they are ready to turn into adults, they develop wings, swim up out of the water and onto the land, and molt one last time into adults. The adults live only 1-2 days.
Photographed by: Christie Remaly. Identified by: KnowYourInsects.org. Location: Club Deb in Knoxville, Tennessee, USA. Date: 6 July 2018.

Unidentified mayfly, exuviae (shed casing).
□ This is the shed casing, or exuviae, of a winged but immature mayfly. Such an immature mayfly is called a subimago. The adult mayfly emerges and leaves behind this exuviae. Mayflies are unusual in that they have an immature version that has functional wings. (Among other winged insects, only the adults have functional wings.) Fly fishermen call the immature, winged mayflies “duns.”
Photographed by: Lori Sughroue. Identified by: Kelly McKinne (@gonzonaturalist). Location: Elk Rapids, Michigan, USA. Date: 31 August 2016.
Lori says, “There were dozens of these in varying sizes, approximately half an inch to this one, about three inches long.”

Unidentified mayfly, exuviae.
□ Look at the amazingly long cerci (the two caudal/tail filaments) on this shed casing of a mayfly!
Photographed by: Victoria Abbott. Identified by: KnowYourInsects.org. Location: United Kingdom. Date: 26 July, 2017.
Victoria says, “I was wondering if you could help ID this wonderful insect. My friend found it on her shed today in the UK. Would be absolutely tremendous to find out what it is.” KnowYourInsects.org loves Victoria’ enthusiasm and we’re happy to help!

Unidentified mayfly, exuviae.
□ The photographer found shed casing of a mayfly near the shore of Lake Erie in the fall. Most mayfly species become adults earlier in the year, but a few hold out until early fall.
Photographed by: Jack Hawkins. Identified by: KnowYourInsects.org. Location: Southern Ontario, Canada. Date: fall 2017.
Jack likens mayflies to straw tail or whydah birds, which have 12- to 14-inch (30-35 cm) straw-like tails, on an island off the southeast coast of Africa.

Unidentified mayfly, exuviae.
□ The photographer spotted this shed casing of a mayfly between the window panes on a jetliner! The wing of the plane is visible through the window. See his comment below.
Photographed and identified by: Geo Christi Eapen. Nice job, Geo! Location: In flight. Date: 26 July, 2017.
Geo says, “I had an unusual sighting of this mayfly exhuviae sitting in the middle glass of of the three-layered aircraft windowpanes and it’s really a mystery how this animal even find its way in to this aircraft.”

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