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Insect Order Ephemeroptera (Mayflies)

Taxonomic Navigation -?-
Kingdom Animalia (Animals)
» Phylum Arthropoda (Arthropods)
» Class Insecta (Insects)
» Order Ephemeroptera (Mayflies)
Family in EphemeropteraNumber of SpecimensNumber of Pictures
AmelitidaeBrown Duns429
BaetidaeBlue-Winged Olives55264
BaetiscidaeArmored Mayflies24127
CaenidaeAngler's Curses925
EphemerellidaeHendricksons, Sulphurs, PMDs, BWOs164740
EphemeridaeHexes and Big Drakes47285
HeptageniidaeMarch Browns, Cahills, Quill Gordons118628
IsonychiidaeSlate Drakes20105
LeptohyphidaeTricos427
LeptophlebiidaeBlack Quills and Blue Quills40210
MetretopodidaePseudo-Gray Drakes1038
Neoephemeridae17
PolymitarcyidaeWhite Flies01
PotamanthidaeGolden Drakes00
SiphlonuridaeGray Drakes840

8 families aren't included.
Common Name
MatchCommon Name
****Mayflies
Fly Imitations by Orvis
Pictures Below
Mayflies may be the most important insects for trout anglers to understand. They are famous outside the fly fishing world for their fragile beauty and short adult lifespan, usually a single day to mate and die. The mayfly's poignant drama attracts poets and fishermen alike, but fishermen make the most of it.

Hatching Behavior

Mayflies live as nymphs for 3 months to 2 years, depending on the species. When they're mature, the entire generation emerges from the stream as adults, often within the span of a couple weeks. They emerge as "duns," an immature winged adult stage, and molt within a day or two into "spinners," the mature adults, which I discuss below.

The duns most often emerge during an hour or two each day for a couple weeks sometime in the spring or summer, though there's great variation between species. These events are barely noticeable in some species and reach nightmarish proportions in others.

There are three ways mayfly nymphs emerge into duns. Most often, the nymph swims to the water's surface and splits open its exoskeleton above the thorax (Thorax: The thorax is the middle part of an insect's body, in between the abdomen and the head, and to which the legs and wings are attached.). The dun wriggles out onto the surface, and many species float along on the surface for a while as their wings dry. These species make prime targets for hungry trout, and they are the dry fly fisherman's favorites. But many important species don't follow this pattern, and anglers benefit from knowing when to match a different style of emergence.

In a some species, the winged dun emerges from its nymphal case several feet underwater and swims to the surface, wings and all. Old-style winged wet flies match these hatches, but newer sparkle yarn patterns work better. Other species emerge by crawling out onto streamside rocks or logs as nymphs. The adults emerge there on land, so they offer little to the angler unless there's enough wind to blow them back into the water. Most writers suggest matching the migrating nymphs when these hatches are underway.

Spinner Behavior

Once mayflies have molted into spinners, they usually gather in swarms over the river to mate. When they're done they usually fall dead, or spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.), on the water. These very coordinated events are often the angler's best chance to see a good rise of trout.

Mayfly females face the extra duty of laying their eggs after mating. Many species release their eggs as they fall spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) on the water. Some land on the water, release a few, and take off again. Others fly low over the water and tip the tips of their abdomens below the surface for just a moment to release eggs. Other species drop their eggs from high in the air. In one very common genus, Baetis, the females land near shore and crawl underwater to lay their eggs in neat little rows on rocks and logs.

Like most things in nature, mayfly spinners aren't as predictable as we'd like. Sometimes clouds of thousands of spinners will gather over a riffle in the evening and fly back into the woods as quickly as they came, never falling spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.).

Spinner falls can happen at any time of day, depending on species, but dusk is by far the most common time. These events are usually much more concentrated than the dun emergence of the same species, which means that many species which are unimportant as duns due to sporadic emergence become very important as spinners.

Some spinner falls take place over every type of water, but most species choose riffles.

Anglers imitating spinners can learn much by carefully watching the real things drifting on the water. Their silhouette and posture does not match the shape of "traditional" spinner patterns; they're more accurately imitated by innovative fly patterns like the Ellis Triple Wing and Galloup's Crippled Spinner described in Kelly Galloup's outstanding book, Cripples & Spinners.

Nymph Biology

Anglers recognize four categories of mayfly nymphs: swimming, burrowing, clinging, and crawling:

  • Some streamlined swimmers move like little bullets, faster then fish of the same size, and they swim upstream against strong current without a problem. Others inhabit slow water and use their speed to dart between leaves in the weed beds.

  • Clingers of the family Heptageniidae are typically flat nymphs with strong legs and claws for holding on to rocks in very fast water. Some have evolved further adaptations for clinging; for example, the genus Rhithrogena has suction-cup-like gills. There is great variation among the clingers and some species have adapted to slow water.

  • Crawlers come in the most varied forms; they are a catch-all group for "average" families which excel at neither swimming nor clinging. The Hendricksons and Sulphurs of the Ephemerella genus are typical crawlers. There are tiny crawlers like Tricorythodes, and there are oddballs like Baetisca. The crawlers in Leptophlebiidae are quite good at swimming, and those in Drunella are quite good at clinging.

  • The distinctive burrowers of Ephemeridae (and the less important Polymitarcyidae) are pale nocturnal creatures which use tusks to carve U-shaped burrows into the river bottom, where they live most of the time. Their long yellow bodies and feathery gray gills make them unmistakable. Their hatches are some of the angler's favorites, especially the giant Hexagenia limbata flies of the Midwest and the Eastern Green Drakes, Ephemera guttulata.



Entomologists have a similar system, but even their line between categories is a blurry one. Some burrowers swim well, some crawlers cling well, and some families, like Potamanthidae, straddle the boundary between categories.

If you fish a fertile stream, watch the bottom ahead of you as you walk. Sometimes, especially in April and May, you'll see lots of mayfly nymphs in front of you swimming out of your way or scurrying to the undersides of rocks. You don't need to be down on all fours with a magnifying glass to see mayfly life underwater.

516 Mayfly Specimens:

Specimen Page:1234...53
Acerpenna (Blue-Winged Olives) Mayfly DunAcerpenna (Blue-Winged Olives) Mayfly DunView 14 PicturesThis dun molted most of the way into a spinner (though the wings got stuck) the evening after I photographed it, so I took some more photos of the spinner.

I found a female nearby, probably of the same species.
Region: Northeast
Collected Sep 19, 2006
Added Oct 4, 2006
Isonychia bicolor (Mahogany Dun) Mayfly SpinnerIsonychia bicolor (Mahogany Dun) Mayfly SpinnerView 15 PicturesI got several really nice pictures of this spinner. I also collected a female on the same trip.
Region: Northeast
Collected Aug 9, 2006
Added Aug 11, 2006
Hexagenia atrocaudata (Late Hex) Mayfly SpinnerHexagenia atrocaudata (Late Hex) Mayfly SpinnerView 12 Pictures
Region: Upper Midwest
Collected Jul 24, 2005
Added Apr 15, 2006
Specimen Page:1234...53

32 Streamside Pictures of Mayflies:

Streamside Photo Page:1234
A thick mating swarm of Tricorythodes mayfly spinners hovers over a cool Catskill tailwater one early fall morning.  View the picture full-size and you'll be able to make out the wings and tails on most of those little white dots.

This was one of many such clouds visible all up and down the river.  The mayflies were impressive, but the trout did not hold up their end of the bargain -- there was not a rise in sight.
A thick mating swarm of Tricorythodes mayfly spinners hovers over a cool Catskill tailwater one early fall morning. View the picture full-size and you'll be able to make out the wings and tails on most of those little white dots.

This was one of many such clouds visible all up and down the river. The mayflies were impressive, but the trout did not hold up their end of the bargain -- there was not a rise in sight.

In this picture: Mayfly Genus Tricorythodes (Tricos).
RegionUpper Midwest
Date TakenSep 2, 2005
Date AddedFeb 9, 2006
This Epeorus pleuralis nymph tried to hatch into a dun while attached to this rock and apparently got stuck.  This species is supposed to emerge from its nymphal shuck on the bottom of the stream and swim to the surface as a bedraggled dun.  It seems more like this one was trying to crawl out onto a rock to emerge.  The rock itself is covered with a thin layer of fast water in a riffle, and apparently it prevented the dun from making any headway.  You can see the dun's eyes and a bit of the mesonotum if you look closely.
This Epeorus pleuralis nymph tried to hatch into a dun while attached to this rock and apparently got stuck. This species is supposed to emerge from its nymphal shuck (
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.
)
on the bottom of the stream and swim to the surface as a bedraggled dun. It seems more like this one was trying to crawl out onto a rock to emerge. The rock itself is covered with a thin layer of fast water in a riffle, and apparently it prevented the dun from making any headway. You can see the dun's eyes and a bit of the mesonotum (Mesonotum: The top of the insect mesothorax.) if you look closely.

In this picture: Mayfly Species Epeorus pleuralis (Quill Gordon).
RegionUpper Midwest
Date TakenApr 19, 2006
Date AddedApr 23, 2006
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This nighttime flash photograph shows a bunch of Ephoron mayflies flying around during the hatch.  So many of them fly around with their dun shucks attached that it seems like they molt from the dun to spinner stage in mid-air.  Actually they molt on streamside vegetation like other mayflies, but they sometimes take off to mate before they're completely finished.
This nighttime flash photograph shows a bunch of Ephoron mayflies flying around during the hatch. So many of them fly around with their dun shucks (
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Here's an underwater view of the pupal shucks of several already-emerged Brachycentrus numerosus caddisflies.
Shuck: The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.
)
attached that it seems like they molt from the dun to spinner stage in mid-air. Actually they molt on streamside vegetation like other mayflies, but they sometimes take off to mate before they're completely finished.

In this picture: Mayfly Genus Ephoron (White Flies).
RegionUpper Midwest
Date TakenAug 14, 2004
Date AddedJan 18, 2006
Streamside Photo Page:1234

67 Underwater Pictures of Mayflies:

Underwater Photo Page:1234...8
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This is my favorite underwater picture so far. It shows a bunch of Simuliidae (black fly) larvae clinging to a rock and swinging in the fast current. There are also at least four visible mayfly nymphs, probably in the family Baetidae.
This is my favorite underwater picture so far. It shows a bunch of Simuliidae (black fly) larvae clinging to a rock and swinging in the fast current. There are also at least four visible mayfly nymphs, probably in the family Baetidae.

In this picture: Mayfly Family Baetidae (Blue-Winged Olives) and True Fly Family Simuliidae (Black Flies).
RegionUpper Midwest
Date TakenMar 19, 2004
Date AddedJan 25, 2006
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This Ephemerella subvaria (Hendrickson) nymph picture is one of my favorites.
This Ephemerella subvaria (Hendrickson) nymph picture is one of my favorites.

In this picture: Mayfly Species Ephemerella subvaria (Hendrickson).
RegionUpper Midwest
Date TakenMar 24, 2004
Date AddedJan 25, 2006
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There's a large Ephemerella subvaria nymph in the top left.
RegionUpper Midwest
Date TakenMar 20, 2004
Date AddedJan 25, 2006
Underwater Photo Page:1234...8

Recent Discussions of Ephemeroptera

Emergence period of green drakes 2 Replies »
Posted by Beardius on Aug 1, 2008 in the species Ephemera guttulata
Last reply on Aug 15, 2008 by Beardius
Emergence periods for green drakes usually run for 7-10 days in most streams. However, there are streams in the east where emergence periods are prolonged by some of the nymphs being parasitized by Nanocladius and Epoicocladius midge larvae. In these streams, emergence may be prolonged to 21 days. Unparasitized nymphs emerge before parasitized nymphs, with each group showing separate peaks of emergence about a week apart. This is based upon my own research on green drake emergence in streams with these midge species.

My question here is this: does anybody know of streams that have this type of prolonged emergence (2-3 weeks) in NY, PA, MD, or WV?
ReplyHex nymph behavior 7 Replies »
Posted by Millerpa on Jun 18, 2006 in the species Hexagenia limbata
Last reply on Aug 8, 2008 by Martinlf
I have read in many places that the Hex nymph is a mud dweller. What does this mean? Does this mean they immediately change from egg to nymph and then burrow into the mud until emergence or do they simply burrow in the mud to find food and spend some time in the open water between meals? I have heard comments from fisherman that indicate they know the hatch has been happening when they see small holes in the muddy banks of the river. This is abit confusing to me. Could someone please clarify.
ReplyTrico Tips 36 Replies »
Posted by Martinlf on Jul 21, 2007 in the genus Tricorythodes
Last reply on Aug 5, 2008 by Martinlf
I'll start with a fly patterns, follow with a bit of what I think I know about Tricos (Entomologists, please offer corrections if needed), and close with a few questions.

I love designing different patterns for Tricos, partly to keep myself entertained, and partly to show the fish something new from time to time. Jason's photos and the opinions of some fussy fish have led me to tie an extra large thorax recently on all my Tricos. My old standby is a parachute tied reverse, with a high vis post over the bend of the hook, and grizzly hackle, with no tails. It's modeled on Al's Trico, which can be found on the Little Lehigh Flyshop website. It's very visible and fish generally approve. My newest fly is a take off from one of Gonzo's (Lloyd Gonzales) patterns in his book Fly-fishing Pressured Water, and it also shows the influence of Al's Trico. Gonzo ties an upside down Trico on a wide gap hook using synthetic material for the wing. I tie this fly also, and it certainly does catch fish, but I recently tied a version with grizzly hackle, making an oversize thorax and palmering hackle over the thorax to create a full wing. I then clipped hackle from the top of the fly (which becomes the bottom, as this is an upside down fly) so that the fly would sit flat, upside down, on my tying table. A drop of Locktite brush-on super glue on the bare recently clipped thorax after darkening the hackle stem with black marker and the fly was done. (By the way, I put tails on this one to balance it [P.S. Later correction: this pattern doesn't need the tails. I've caught plenty fish now on a tailless version] .) It caught several fish the first time I tried it on a heavily fished stream.

I believe for some, if not most species of Tricos, males hatch at night, females in the morning, and that the spinners fall when the air temperature hits the upper 60's. This generally means that as the season goes on, spinners hit the water later and later. Sometimes by 7:00 am (or earlier) in the early summer, by 10:00 (or later) in the fall.

It's been unseasonably cool in the Northeast the past couple of days, and I would have gone out this morning but for taking my daughter to a midnight showing of The Order of the Phoenix (I just couldn't get up) but I'm wondering if the spinner fall happens later than normal on cool mid-summer mornings like today's. I hope to find out Monday, but am curious if anyone has experiences to share. Also, does anyone have an effective Trico pattern to share? I'm always looking for ideas.
ReplyI agree with the nymph and emergence coments above
Posted by Beardius on Aug 1, 2008 in the species Litobrancha recurvata
Caucci and Nastasi's comments and other comments above are correct. They are really hardy and impressive nymphs when they near maturity. Litobrancha nymphs prefer fine silty, mucky habitats in streams. They can be abundant in mucky side channels to the main stream. Their emergence occurs over a 5-day span, with the large majority emerging within a 3-day period. Therefore, large emergences are rarely encountered. When they do occur, they can be very impressive.

From my experience collecting and rearing these critters, they have a 2-year life cycle in PA and MD. They increase tremendously in size in their second year. Emergence occurred in late May into early June about a week before that of green drakes (Ephemera guttulata).
ReplyThe Rise: What can we learn? 4 Replies »
Posted by MarkA on Jul 7, 2008
Last reply on Jul 8, 2008 by Jjlyon01
The Rise: What can we learn?

I am new to trout fishing. The last two weeks I have been exposed to two different trout rises and takes. Neither time have I been able to observe what was on the water. Little brownish flys were in the air.
The first week I what I would describe as a ballistic rise (take). It was if rocks were being thrown in the water. Very large splashes and loud noise in the water were this rises trademark.

This week the rise was that of whale scooping up krill. The fish came to the surface with its mouth open, dorsal and tail fins above water. It would stay above water briefly and then quietly submerge. Again I did not see anything on the water but there was a cloud of flys above.
My buddy says it is different stages in the fly life cycle and I would agree, but what stages. Any help/comments are appreciated.
Reply
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