Mayflies are one of the most ancient and fascinating groups of aquatic insects, known for their delicate beauty, short adult lifespans, and important role in freshwater ecosystems. Found in rivers, lakes, and streams worldwide, these insects belong to the order Ephemeroptera and include hundreds of species across various genera. In this guide, we explore 21 notable types of mayflies—from tiny Tricos to the large Hexagenia—each with its unique appearance, habitat, and life cycle traits. Whether you’re a nature enthusiast, fly angler, or simply curious about aquatic life, this list offers an insightful look into the world of mayflies.
1. Baetis Mayfly
Baetis is one of the most widespread and diverse genera of mayflies, commonly found in freshwater streams and rivers across North America and Europe. These mayflies are small, fast-swimming, and are a favorite among fly anglers due to their active nymph stages and prolific hatches.
Identification
- Small size, typically 5–10 mm in length
- Olive to brown body coloration
- Two long, slender tails (cerci)
- Clear wings with distinct venation
- Nymphs have streamlined, torpedo-shaped bodies
- Gills located on the abdomen, often plate-like
Habitat
Baetis mayflies prefer cool, clean, and well-oxygenated streams with moderate current. They are especially abundant in riffle zones where rocks and gravel provide good shelter.
Behavior
Baetis nymphs are agile swimmers and often dart through the water column. Adults have brief lifespans and are typically seen flying low over the water during emergence.
Diet
As nymphs, Baetis feed on algae, diatoms, and fine organic matter scraped from submerged rocks and vegetation.
Reproduction
Adults emerge in large synchronized hatches, often triggered by temperature or light changes. Mating takes place in flight, after which females lay eggs on or under the water surface.
2. Ephemera danica
Ephemera danica, commonly known as the Green Drake, is one of the most recognizable large mayflies in Europe. It is especially popular among fly fishers due to its prominent emergence and sizable appearance. This species plays a vital role in freshwater ecosystems as both prey and a bioindicator of water quality.
Identification
- Large body, up to 25 mm in length
- Pale green to yellowish body with dark banded legs
- Two or three long, delicate tails
- Broad, heavily veined wings that are held upright when at rest
- Nymphs are robust with well-developed gills and burrowing legs
- Prominent tusks or frontal protrusions on the head of nymphs
Habitat
Ephemera danica thrives in slow-moving rivers, large streams, and lakes with sandy or silty bottoms where nymphs can burrow deeply into the substrate.
Behavior
The nymphs are burrowers and spend most of their life underground. Emergence typically happens in late spring or early summer, often in the evening. Adults are short-lived, usually surviving only 1–2 days.
Diet
Nymphs feed on fine organic particles filtered from the sediment. Adults do not feed; they rely on energy stored during the nymphal stage.
Reproduction
After mating mid-air, females deposit their eggs in the water. These eggs sink to the bottom, where they hatch into burrowing nymphs. The full lifecycle can last one to two years.
3. Hexagenia limbata
Hexagenia limbata, also known as the Giant Mayfly or Burrowing Mayfly, is one of the largest mayfly species in North America. Their synchronized mass emergences over lakes and rivers often attract public attention due to their sheer volume and short adult lifespan.
Identification
- Large body length up to 30 mm
- Light brown to tan coloration with yellowish legs
- Three long, filamentous tails
- Prominent upright wings with strong venation
- Nymphs are soft-bodied with large tusks for digging
- Fringed abdominal gills for breathing in sediment
Habitat
Common in soft-bottomed lakes and slow-moving rivers, especially across the Midwest and Great Lakes regions. Nymphs burrow deep into the mud or silt, making them essential for sediment turnover.
Behavior
Hexagenia nymphs are burrowers, rarely seen unless unearthed. Emergence occurs in early to mid-summer, often at dusk, with swarms visible around water bodies and lights. Adults are strong flyers but only live a few days.
Diet
Nymphs consume detritus and organic particles in the mud. Adult mayflies do not eat, as they lack functional mouthparts.
Reproduction
Adults mate in flight. After mating, females lay eggs directly onto the water surface. The eggs sink and hatch into nymphs that will live for a year or more before emerging as adults.
4. Isonychia bicolor
Isonychia bicolor, often referred to as the Slate Drake or Mahogany Dun, is a fast-swimming mayfly found in clean, cool-running streams and rivers. It is favored by anglers due to its extended hatching season and larger size compared to many other mayflies.
Identification
- Medium to large size, about 10–15 mm long
- Dark brown to slate-gray body with pale legs
- Two tails (unlike many mayflies that have three)
- Smoky or dusky-colored wings
- Nymphs have strong legs and a dark stripe along their back
- Fringe of fine hair along the front legs used in feeding
Habitat
Prefers well-oxygenated streams with moderate to fast currents. Nymphs cling to submerged rocks or debris in riffles and runs.
Behavior
Nymphs are excellent swimmers and often cling or crawl rather than burrow. Adult Isonychia mayflies emerge over several months, offering a long season for observation or fly-fishing.
Diet
Nymphs are collectors and filter feeders, trapping small organic particles from the current with their hairy forelegs.
Reproduction
After mating in the air, females fly over the water and dip their abdomens to release eggs. These settle on the substrate and hatch into active nymphs.
5. Ephoron leukon
Ephoron leukon, also called the White Fly, is a late-summer emerging mayfly found in warm, large rivers across North America. It is known for its pale coloring and mass evening emergences that draw attention from fish, birds, and humans alike.
Identification
- Medium size, around 8–12 mm in length
- Pale cream to white body and wings
- Three delicate tails
- Males have large, bulbous eyes
- Nymphs have soft bodies and are burrowers
- Frilly gills along the abdomen aid in respiration
Habitat
Prefers large, slow-flowing rivers with muddy or silty bottoms where the nymphs burrow and feed undisturbed.
Behavior
Ephoron leukon emerges in great numbers at dusk, typically in July and August. Adults live only a few hours and do not eat.
Diet
Nymphs feed on organic debris within the sediment. Adults do not feed at all.
Reproduction
Adults mate in large aerial swarms, often just before dark. Females quickly lay eggs on the water surface, which sink and begin the cycle again. The lifecycle completes in about one year.
6. Callibaetis
Callibaetis mayflies are small but highly adaptable insects commonly found in still or slow-moving waters such as ponds, lakes, and marshes. Known as the Speckled Duns, they are one of the few mayfly genera well-suited to calm waters.
Identification
- Small size, about 5–8 mm in length
- Mottled or speckled wings with distinct spotting
- Slender, light brown or grayish body
- Three fine tails
- Nymphs are elongated with mottled patterns and feathery gills
- Wing venation is more irregular compared to other mayflies
Habitat
Found in lakes, ponds, and the quiet backwaters of rivers. Their nymphs thrive in aquatic vegetation and silty bottoms.
Behavior
Callibaetis is one of the few mayflies with multiple generations per year (multivoltine), especially in warm climates. Emergence often occurs during mid-morning under calm, sunny conditions.
Diet
Nymphs feed on algae, biofilm, and microscopic plant material. Adults do not feed.
Reproduction
Females drop their eggs onto the water surface while flying low or dipping. Eggs sink and hatch quickly, allowing for several cycles in one season.
7. Drunella
Drunella mayflies, commonly known as Blue-Winged Olives (though some species vary), are robust, cold-water-loving insects often found in mountainous and forested streams. They are important for both aquatic ecosystems and fly fishing.
Identification
- Medium size, around 6–12 mm in length
- Stout body with olive, green, or brown hues
- Clear wings with blueish tinge
- Two or three tails
- Nymphs have flat, broad bodies with heavily armored thoraxes
- Pronounced legs and fringed gills
Habitat
Found in cool, high-elevation streams with strong currents. Their flattened body shape helps them cling to rocks in fast water.
Behavior
Drunella nymphs are clingers, well-adapted to resisting swift flows. Emergence is often sporadic, with adults flying low over riffles in spring and early summer.
Diet
Nymphs graze on algae and organic debris coating submerged stones.
Reproduction
After aerial mating swarms, females deposit their eggs by dipping into fast-moving sections of streams. Eggs settle between gravel and hatch into tough, clingy nymphs.
8. Caenis
Caenis mayflies, often called Angler’s Curse due to their tiny size and dense hatches, are one of the smallest mayflies found in freshwater habitats. Despite their size, they are incredibly abundant and play a significant role in aquatic food chains.
Identification
- Very small size, typically 3–5 mm in length
- Pale to white body with delicate features
- Three short tails
- Wings are proportionally large and clear
- Nymphs are flattened and compact with frilly gills
- Often appear dust-like during mass emergence
Habitat
Commonly found in lakes, ponds, and slow-moving rivers with silty or muddy bottoms. They thrive in both clean and slightly nutrient-rich waters.
Behavior
Emergences occur in massive swarms, typically at dawn or dusk during summer months. Adults are short-lived and can cover the water’s surface in white clouds.
Diet
Nymphs feed on algae and detritus scraped from bottom sediments. Adults do not feed.
Reproduction
Females scatter eggs on the water’s surface after mating. Eggs hatch quickly, and the nymphs develop over several months, often with more than one generation per year.
9. Paraleptophlebia
Paraleptophlebia mayflies, sometimes referred to as Blue Quills, are early spring emergers in cool, clean streams. These slender mayflies are among the first aquatic insects to hatch after winter, making them important indicators of water quality.
Identification
- Small to medium size, 6–10 mm long
- Slender body with dark brown or bluish-gray hues
- Two tails
- Wings are upright and finely veined
- Nymphs are streamlined with large gills and pointed heads
- Legs are relatively long and adapted for crawling
Habitat
Prefer cool, shaded forest streams and spring creeks with gravel or rocky bottoms. They avoid heavily silted or polluted environments.
Behavior
Nymphs are agile crawlers, hiding beneath rocks or among submerged vegetation. Emergence begins in early spring and often lasts several weeks depending on temperature.
Diet
Nymphs graze on microscopic algae, plant detritus, and diatoms on rock surfaces. Adults do not eat.
Reproduction
Mating swarms form in open spaces above streams. Females dip their abdomens on the water to lay eggs, which sink to the bottom and hatch into new generations.
10. Leptophlebia
Leptophlebia mayflies, often referred to as Black Quills or Brown Duns, are graceful, slow-emerging species found in cool waters. They are appreciated for their elegant flight and relatively large size among the Leptophlebiidae family.
Identification
- Medium size, typically 8–14 mm in length
- Dark brown or blackish body with reddish or rusty tones
- Two tails
- Large, rounded wings with a smoky tint
- Nymphs are slender and have paddle-shaped gills on the sides of the abdomen
- Prominent legs and antennae
Habitat
Inhabit slow to moderately flowing streams and lakes with sandy or gravel bottoms. Nymphs often live among submerged vegetation or debris.
Behavior
Emergence typically takes place in spring or early summer, often in calm evening conditions. Adults are delicate flyers and rest with wings held vertically.
Diet
Nymphs feed on detritus, algae, and fine organic particles. Adult Leptophlebia mayflies do not eat.
Reproduction
After aerial mating, females descend to the water surface and release eggs. Eggs sink and adhere to substrates, hatching into nymphs that spend months developing underwater.
11. Ameletus
Ameletus mayflies are early-season insects that emerge in the spring from cold, fast-flowing streams. Known as Brown Duns or sometimes simply Spring Mayflies, they are especially abundant in northern and mountainous regions.
Identification
- Medium-sized, usually 8–12 mm long
- Brown to reddish-brown body
- Two or three tails
- Wings are clear with well-defined venation
- Nymphs are elongated with long tails and feathery gills
- Often have a dark stripe down the back
Habitat
Prefers high-elevation or northern cold streams with gravel or rocky beds. They are usually found in riffle areas where the current is strong and oxygen levels are high.
Behavior
Ameletus nymphs are agile swimmers and often drift with the current when dislodged. Adults emerge in late winter to early spring and are one of the first insects available to fish after ice melts.
Diet
Nymphs consume periphyton, biofilm, and algae from rock surfaces. Adults, like most mayflies, do not feed.
Reproduction
Mating occurs in air. Females release eggs into the stream shortly after mating. Eggs settle into gravel and hatch as water temperatures rise. The full lifecycle usually completes within a single year.
12. Cinygmula
Cinygmula mayflies are less commonly known but important cold-water species found mainly in mountain and northern streams. They are closely related to the Heptageniidae family and are appreciated for their early and extended hatching behavior.
Identification
- Medium size, typically 8–13 mm long
- Yellowish to light brown body with darker markings
- Two or three tails
- Clear to lightly smoky wings with visible venation
- Nymphs have flat, wide bodies and sprawling legs
- Gills are plate-like, located along the abdomen
Habitat
Common in fast-flowing, well-oxygenated mountain streams, especially in colder regions. Nymphs cling to rocks and logs in riffles and runs.
Behavior
Nymphs are strong clingers that resist current by flattening themselves against surfaces. Adults often hatch during daylight in cool conditions, especially in spring and early summer.
Diet
Nymphs feed on algae, diatoms, and fine organic detritus scraped from submerged stones. Adults do not feed.
Reproduction
After mating flights, females dip or skim the water surface to release their eggs. The eggs settle in clean gravel beds and hatch into streamlined nymphs within weeks.
13. Heptagenia
Heptagenia mayflies are widespread and commonly observed species belonging to the flatheaded mayfly group. Known for their clingy nymphs and stable populations, they are important indicators of healthy streams.
Identification
- Medium size, around 8–14 mm in length
- Yellowish to olive body with banded legs
- Two tails (sometimes three)
- Wings are upright and transparent
- Nymphs have flat heads, broad thoraxes, and stout legs for clinging
- Gills appear as overlapping plates on the abdomen
Habitat
Prefers clear, fast-flowing rivers and creeks with rocky or gravel bottoms. Nymphs are abundant in riffles where water flow is strongest.
Behavior
Heptagenia nymphs cling to undersides of rocks and avoid strong currents by remaining flat. Adult emergence varies by species but usually occurs in late spring or summer.
Diet
Nymphs graze on algae, microbial film, and organic particles found on rock surfaces. Adults do not eat during their short lives.
Reproduction
Mating occurs in air, typically in the evening. Females deposit their eggs by dipping them into flowing water. Eggs hatch into sturdy nymphs that grow slowly over several months.
14. Ephemerella
Ephemerella mayflies, often known by anglers as Sulphurs or Hendricksons (depending on the species), are among the most important and widely distributed mayflies in North America and parts of Europe. They are prized in fly fishing due to their predictable hatches and delicate appearance.
Identification
- Small to medium size, about 6–12 mm in length
- Coloration varies: yellow, olive, tan, or reddish tones
- Two or three tails
- Upright, transparent wings with fine venation
- Nymphs are stocky with three tails and saw-like gills on the abdomen
- Characteristic intersegmental bands on nymphs
Habitat
Found in cold to cool streams, rivers, and spring creeks with gravel or rocky bottoms. They prefer slower riffles and pools with good water quality.
Behavior
Ephemerella nymphs are crawlers, often hiding in gravel and vegetation. Emergence occurs gradually, typically from spring into early summer, depending on the species and water temperature.
Diet
Nymphs feed on detritus, algae, and microorganisms on submerged surfaces. Adults do not eat during their brief lifespan.
Reproduction
After aerial mating, females lay eggs in clumps or trails on the water surface. The eggs sink and attach to rocks or vegetation, hatching within weeks into juvenile nymphs.
15. Serratella
Serratella mayflies are closely related to Ephemerella and were once considered part of that genus. Known for their early hatches and distinctive abdominal spines, these mayflies are found in cool streams across North America.
Identification
- Small to medium size, 5–10 mm long
- Light olive to rusty brown body
- Two or three tails
- Clear, upright wings with fine venation
- Nymphs resemble Ephemerella but have serrated spines on the abdomen
- Gills are fringed and extend outward from the body
Habitat
Common in cool, clean streams with moderate flow. Nymphs dwell in leaf packs, among rocks, and in aquatic vegetation.
Behavior
Serratella nymphs are crawlers and occasionally active swimmers. Adult emergence may begin in early spring and continue into summer in higher elevations.
Diet
Nymphs graze on algae, microbial films, and small organic debris. Adults do not consume food.
Reproduction
Mating occurs in small aerial swarms. Females deposit eggs on the surface or directly into the stream, which hatch into serrated nymphs that develop over several months.
16. Rhithrogena
Rhithrogena mayflies, often known as the Flatheaded Clinger mayflies, are important cold-water species found in pristine mountainous streams and rivers. They are essential indicators of excellent water quality and are frequently seen early in the mayfly season.
Identification
- Medium to large size, 8–14 mm in length
- Brown to reddish-brown body
- Two or three tails
- Wings are upright and usually clear with dense venation
- Nymphs are flat-bodied with broad heads and strong legs
- Gills are flat and plate-like, extending over the abdomen
Habitat
Primarily found in fast-flowing, well-oxygenated mountain streams and rivers. Nymphs cling to rocks and boulders in riffles and runs.
Behavior
Rhithrogena nymphs are excellent clingers and remain close to the substrate to resist strong current. Adults tend to emerge during daylight, especially in spring and early summer.
Diet
Nymphs feed on periphyton (a mix of algae and microbes) and organic debris scraped from stones. Adults do not feed.
Reproduction
After mating, females drop eggs into the stream while flying low or skimming the surface. Eggs sink into clean gravel beds, hatch, and nymphs develop over 1–2 years in colder regions.
17. Tricorythodes
Tricorythodes mayflies, often called Tricos, are tiny but incredibly prolific insects known for their massive morning hatches in late summer. Despite their small size, they are a critical food source for trout and other aquatic predators.
Identification
- Very small size, usually 3–5 mm in length
- Pale gray to white or black body, depending on the species and gender
- Three very fine tails
- Delicate, upright wings
- Nymphs are compact with short legs and well-developed gills
Habitat
Found in warm, slow-moving rivers and streams, especially those with silty or sandy bottoms and abundant aquatic vegetation.
Behavior
Nymphs are bottom-dwellers, moving slowly among sediment and plants. Adults hatch in huge swarms early in the morning, often just before sunrise, with males emerging first followed by females.
Diet
Nymphs consume fine detritus and microorganisms from the sediment. Adults do not feed.
Reproduction
After short mating flights, females return to the water and drop eggs on the surface. Eggs hatch rapidly in warm conditions, and some regions see multiple generations per season.
18. Maccaffertium
Maccaffertium mayflies, commonly known as March Browns or Gray Foxes depending on the species, are widespread in North America. These medium-sized mayflies are known for their predictable spring hatches and are a favorite among anglers.
Identification
- Medium to large size, about 10–15 mm in length
- Body color ranges from mottled brown to gray or tan
- Two or three tails
- Wings are upright and grayish or smoky, with clear venation
- Nymphs have flat, broad bodies and wide heads
- Gills are plate-like and visible on most abdominal segments
Habitat
Inhabit moderate to fast-moving rivers and streams with clean gravel or cobble bottoms. Nymphs live among rocks and submerged wood.
Behavior
Maccaffertium nymphs are clingers that move slowly along rocks. Adult hatches occur in late spring and early summer, typically during the afternoon or early evening.
Diet
Nymphs scrape algae, diatoms, and organic matter from rocks. Adults do not feed.
Reproduction
Mating occurs in flight. Females deposit eggs by dipping them into the water surface. The eggs sink and hatch into nymphs that take up residence in riffles and runs.
19. Siphlonurus
Siphlonurus mayflies, sometimes referred to as Gray Drakes, are stillwater and slow-current specialists. These elegant mayflies are more commonly found in lakes and ponds than in rivers, which is unusual among mayflies.
Identification
- Medium size, usually 10–14 mm in length
- Slender, gray to brown body
- Three long, trailing tails
- Wings are clear with few cross-veins
- Nymphs are cylindrical and adapted for swimming
- Gills are forked and feathery along the abdomen
Habitat
Common in stillwaters, including lakes, ponds, and marshes. Nymphs swim freely among submerged vegetation and debris.
Behavior
Siphlonurus nymphs are active swimmers, unlike many other bottom-dwelling mayflies. Emergence often occurs in early summer and can happen directly from the water surface or from shoreline vegetation.
Diet
Nymphs consume algae and fine organic matter suspended in the water or settled on plants. Adults do not eat.
Reproduction
Adults mate in swarms above still water. Females drop eggs onto the surface or among shoreline vegetation. Eggs hatch into swimming nymphs that can take several months to mature.
20. Epeorus
Epeorus mayflies, often referred to as Quill Gordons, are early-season clinger mayflies found in cold, swift streams. They are easily recognized by their single tail and fast emergence patterns, making them a key part of the spring trout diet in many regions.
Identification
- Medium size, typically 8–12 mm in length
- Grayish to olive-brown body
- One single central tail (unusual for mayflies)
- Upright, clear wings with prominent venation
- Nymphs have a flattened body with large, plate-like gills
- Front legs are elongated, helping them cling to surfaces
Habitat
Epeorus species inhabit cold, rocky, high-gradient streams and rivers. Nymphs cling to the undersides of rocks in fast riffles and require high oxygen levels.
Behavior
Nymphs are powerful clingers and resistant to displacement by current. Emergence typically occurs in early spring, often during sunny afternoons, making them a favorite among early-season fly fishers.
Diet
Nymphs graze on algae and periphyton growing on rock surfaces. Adults, like most mayflies, do not eat.
Reproduction
Mating occurs quickly, and females lay eggs by dipping or skimming the surface of the stream. The eggs sink into gravel and hatch into clinging nymphs, which may take a year to develop.
21. Potamanthus
Potamanthus mayflies are large and strong swimmers found in big, warm rivers. Known as Golden Drakes or River Drakes, they stand out with their size and active emergence behavior.
Identification
- Large size, often 15–20 mm long
- Yellow to golden-brown body
- Three long, elegant tails
- Wings are clear with golden veins and held upright
- Nymphs are streamlined swimmers with long legs
- Gills are feathery and extend from each abdominal segment
Habitat
Prefer large, warm rivers with sandy or silty bottoms. Nymphs are active swimmers that reside in areas with slow to moderate currents.
Behavior
Potamanthus nymphs are among the few swimming mayflies that are agile and active. Emergence usually occurs at dusk or into the night during summer months, often in large numbers.
Diet
Nymphs feed on organic debris and fine particles suspended in water. Adults do not consume food.
Reproduction
Mating flights occur at dusk. Females scatter eggs over the water surface, and eggs sink to the riverbed. The nymphs develop over several months before transforming into adults.