Mayflies are fascinating insects known for their unique life cycle. These delicate creatures play a vital role in ecosystems, contributing to nutrient cycling and serving as food for various predators. The life cycle of a mayfly comprises several stages, including the egg, larval (nymph), subimago, and adult (imago) stage1. Each stage plays a crucial role in the overall development and reproduction of the mayfly.
Mayfly eggs are laid on water surfaces, where they quickly sink to the bottom before hatching into aquatic nymphs[^2^]. These nymphs, also known as naiads, can live underwater for months to years, breathing through gills while foraging on organic debris and algae[^3^]. Once the nymphs are ready to emerge, they transform into subimagos – an active, mobile phase unique to mayflies.
Life Stages of the Mayfly
- Mayfly nymphs, also known as naiads, live underwater for months to years.
- They crawl around rocks and vegetation, feeding on organic matter.
- The subimago stage is unique to mayflies among extant insects.
- It is an active and mobile stage between the ultimate larval instar and the mature adult stage (imago).
- Mayflies are the only insects to have two “adult” molts, reaching the imago stage after passing through the subimago stage.
- Imago mayflies have a short life span, lasting only a few minutes to a few days depending on the species, with the sole purpose of mating before they die.
|Nymph||Months to years||Underwater, around rocks and vegetation||Feeds on organic matter|
|Subimago||Between nymph and imago||Transitioning from underwater to above water||Active and mobile stage|
|Imago||Few minutes to few days||Above water, mates and then dies||Two “adult” molts, short lifespan|
Rivers and Streams
Mayfly larvae, also known as nymphs, are commonly found in rivers and streams. They often have flattened heads which help them adhere to rocks in fast-flowing water1. Some specific characteristics of mayfly nymphs in rivers and streams include:
- Sharp claws: Nymphs have sharp claws for clinging onto rocks and stones.
- Gills: They have leaf-like or feathery external gills for breathing underwater.
Ponds and Lakes
Although less common, some species of mayflies can thrive in ponds and lakes1. The primary differences in the habitats may affect the nymphs’ features and behaviors:
|Rivers and Streams||Ponds and Lakes|
|Fast-flowing water||Slow-moving or still water|
|Flattened head for adhering to rocks||May have a less flattened head|
|Sharp claws for clinging to rocks||Less need for sharp claws|
In these environments, mayfly nymphs may display different adaptational traits:
- Swimming: Nymphs in ponds and lakes may be better adapted for swimming than their river-dwelling counterparts.
- Depth preferences: They may prefer different depths, depending on the available resources and water conditions.
Importance in Ecosystem
Mayflies play a vital role in the ecosystem. They serve as an essential food source for various predators like fish, birds, and amphibians. Some examples of animals that feed on mayflies include:
Pros of mayflies in the ecosystem:
- Contribute to the food chain
- Help recycle nutrients in aquatic ecosystems
Cons of mayflies in the ecosystem:
- Mayfly swarms can cause inconvenience for humans, especially near rivers or lakes
Indicator of Water Quality
Mayflies are considered an excellent indicator of water quality. A healthy population of mayflies can signal good quality water and a well-functioning ecosystem. On the other hand, the absence or decline of mayflies may suggest water pollution or degraded habitat.
|Water Quality||Mayfly Population|
In conclusion, mayflies serve as important components of the ecosystem and help us assess water quality, contributing to the overall health of our environment.
Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.
Letter 1 – Possibly Mayfly Exuvia
Subject: larvae insect
Location: Los Angeles
August 19, 2016 4:08 am
Since a week, my house wall outside is filled with 100-200 tiny larvae.
I live in Los Angeles. I would say they are 4-5mm long maybe.
Do you live near the LA River or some other body of water? Or, do you have a pond in your yard? This looks like the aquatic larva of a Mayfly, or more accurately, the exuvia of a Mayfly. When they near maturity, the aquatic naiads climb out of the water and molt, flying off as a subadult. The subadult of a Mayfly is one of the only insects that molts a second time once it is winged, eventually emerging as a mature adult Mayfly. Since the larvae are aquatic, they need a body of water in which to develop. Do the larvae move? If not, then they are simply the exuviae, or cast-off exoskeletons.
Thanks for your answer.
We live about 2 blocks ~8 minutes walk from the LA river which is really the suburban area…all concrete.
There are 2 swimming pools nearby neighbors, but they are usually taking care if them. Otherwise no other water besides sprinklers.
Letter 2 – Mayfly: Angler's Blue Winged Olive
Little mayfly tempting me to skip work
Location: Yakima, WA
November 12, 2010 6:53 pm
I came into my office one morning in late March and found this little Baetis mayfly, or ”blue winged olive” as anglers know them, on my computer screen, tempting me to blow off work and go fly fishing. Oh, well, Windows is known to be buggy.
Signature: Paul Huffman, President-for-Life, Moclips Surf Club
Hi again Paul,
There can never be too many opportunities to hang the “Gone Fishing” sign. Thanks for relaying the Blue Winged Olive moniker. We will link to the genus Baetis on BugGuide.
Letter 3 – Mayfly, but what species???
Hexagenia limbata ?? Lovely and yellow
Mon, Jul 6, 2009 at 5:33 PM
Dear Bug Person,
As a family of amateur naturalists, we implore you to help us correctly identify this lovely yellow specimen my son found near the banks of the James River today. We’d love to be able to add it’s name to our nature journals! It was struggling to fly when we found it and lifted it to a branch so it could be upright.
A Thousand Thanks
Sincerely, The Farmer Family
Dear Farmer Family,
We cannot say for certain that this Mayfly is Hexagenia limbata, but that is a good possibility based on the images posted to BugGuide. We will post your letter and hopefully, one of our readers who knows more about the order Ephemeroptera will be able to provide a definite answer. We do believe this is a subimago, or preadult and that it will molt one more time before becoming a true reproductive adult with clear wings. You may read more about Mayflies on BugGuide.
Letter 4 – Mayfly Metamorphosis
and some mayflies
I thought you might want to take a look at this bug that I noticed in my car while driving. It was right in front of my fiancee’s face, but she didn’t see it. I stopped the car and told her to get out, and took this picture. If she had noticed it first, I’m sure we would have crashed, because let’s just say she doesn’t share my love of insects! Anyway, from the best I can tell, this is a large mayfly. I have seen some photos of the genus Hexagenia that look somewhat similar, but I know next to nothing about these. I assume the other thing in the picture is the result of a molt similar to what we see from cicadas?What do you think? Keep up the good work!
P.s. the two images are the same, but one is rotated. I wasn’t sure which one had better feng shui.
Hi again Bobby,
Though we have never really thought of the fact that we rotate images so they will better fit the format of our site as being feng sui, that is kind of correct. Also correct on the Mayfly metamorphosis identification, though we would not commit to a genus name on this.
Letter 5 – Mayfly Metamorphosis
Is this a dragonfly?
In the past few days I’ve seen lots of these yellow insects hanging around outside work. Today I saw this one that had just emerged from its former body and had to take a closeup photo of the two. It is an awesome looking bug; is it a dragonfly? Thanks,
(found in Chesterfield, Missouri)
Don’t let the name fool you. Even though it is September, this is a Mayfly. Like dragonflies, the aquatic nymphs are known as Naiads. Mayflies do not feed as adults and sometimes appear in great numbers, only to disappear in a few days to return the following year.
Letter 6 – Mayfly Metamorphosis
I was vacationing last week in Salt Creek, NY along the Wappinger Creek and took a double portrait of this bug which was resting nears it’s newly shed exoskeleton & just thought I would share.
What a wonderful photo of a newly metamorphosed Mayfly. Despite their name, Mayflies mature during other months as well. Adults only live a few days, long enough to mate..
Letter 7 – Mayfly Naiad
New species of a water bug?
Hey bug guys,
Here on vacation in Minnesota, we spend plenty of time in lake Kabekona, the lake we’re staying at. However, picking up and moving rocks today, this little bugger somehow found his way to my finger, just kind of hung on but wasn’t really holding on too tightly to me. He acted like a fish out of water on my finger, didn’t move or do anything, I thought I accidentally killed it trying to find a frisbee to put water in so it would be happy. After putting it back in some water, it perked up and swam around using it’s 6 legs and 3 tails, awkward looking little guy.. I was hoping you guys could tell us if this is maybe a parasite or just another weird bug, he was very small only about a quarter of an inch, perhaps a little less. Thanks for your time, hope to hear back from you soon!
This is an immature Mayfly, known as a Naiad. Mayflies belong to the order Ephemeroptera. Adults do not feed and only live a few days. Naiads feed on algae and microscopic organic debris.
Letter 8 – Mayfly Naiad
Is this a water scorpion?
Location: Woodacre, CA
September 12, 2010 11:30 am
We live in west Marin County, CA. My son Jonah and I found this small bug in the water at the edge of our local creek on April 21, 2010. My son, who was 6-1/2 at the time, casually commented that it looked like a scorpion, and dubbed it ”water scorpion.” Last night when I was looking at other bugs on your web site, I saw that there is a bug called a water scorpion. Did my son hit the nail on the head?
Signature: Mark & Jonah
Hi Mark & Jonah,
Your insect is not a Water Scorpion. This appears to us to be the aquatic nymph of a Mayfly in the order Ephemeroptera, and like other aquatic nymphs, it is commonly called a Naiad. It bears a close resemblance to the nymphs in the genus Epeorus, as evidenced by this image on BugGuide.
Letter 9 – Mayfly Nymph
Subject: Strange prehistoric water dweller
Location: Little grass valley reservoir california
July 2, 2017 7:21 pm
This bug was caught chasing my husband as we swam in a lake. It has what looks like feathers along it’s back side and pinchers.
This is the aquatic nymph or naiad of a Mayfly in the order Ephemeroptera. Anglers often devote major portions of websites to insects used as bait, so we found nice images that match yours posted to Fly Fishing God and Trout Nut as well as on BugGuide. According to BugGuide: “most nymphs develop in streams and rivers that are well-oxygenated and relatively free of pollution; some species develop in lakes or ponds, usually in shallow water where the oxygen content is highest.”
Letter 10 – Mayfly on Steroids!!!
Wanted to start off by telling you what a fantastic site you have. I must say that your site has given me a new appreciation for the wonderful and beautiful world of bugs. As a person who used to think bugs were yucky, I now find myself instead seeking them out. I was hoping that I’d find something interesting for you to identify so when I found this little guy hanging out on a wall, I got excited. However, I was quite disappointed at how easily I found my answer on your site. Either way i wanted to share this gorgeous insect with you, which I am almost certain is a mayfly, in July in the San Joaquin Valley. Thanks for your time, and of course, keep up the good work!
Goodness Gracious Kelly,
Are your Mayflies in the San Joaquin Valley on steroids? It is nearly as large as that VW Beetle.
Letter 11 – Mayfly, but which species????
Subject: march brown or sulphur?
Location: western maryland, usa
May 16, 2014 4:47 am
March Brown or Sulphur? In a debate with a buddy. North Branch Potomac river, May 13, 2014
This debate will most likely take someone with far greater Mayfly identification skills than our own. From our research, the March Brown is a European species, Rhithrogena germanica, and it is not found in North America, so we would eliminate that as an identity of the individual in your images. The images of the March Browns on the First Nature website have patterned wings like the ones in your submitted images, but the pattern appears to be distinctly different. According to Trout Nut, the Sulphur Dun is Ephemerella invaria, and that species, as pictured on BugGuide, does not have patterned wings, so we don’t believe that is the correct identity for this Mayfly either. We tried browsing through the images on BugGuide, and this might be Hexagenia bilineata based on this BugGuide image as well as this Bugguide image. We are looking at the darker border on the hind wings and the shape of the eyes as distinguishing features. There is no common name for Hexagenia bilineata on BugGuide, however the genus is know collectively as the Giant Mayfly, Golden Mayfly or Burrowing Mayfly, according to BugGuide. Since BugGuide readers have different interests than anglers, and we are guessing you and your buddy are anglers, we tried to learn if there is a common name for Hexagenia bilineata among trout fishermen. There is no common name on Trout Nut, but the site does state: “These are huge mayflies. Hexagenia limbata, by far the most important species, is the second largest mayfly in the United States.” Again we cannot confirm that our identification is correct, but we believe you are both incorrect.
Thanks for the info The insect was approximately a #12 (fly fisherman sizing) I think the bilineata is a much larger (#06-08) mayfly than the one I sent. Any other ideas? PJ
Letter 12 – Mayfly with detritus
Subject: Bug with a flower butt?
May 26, 2013 4:44 am
I saw this bug last summer at Smith Mountain Lake, Virginia (near Roanoke). It is on a size 10 flip flop in the photo. And it appeared to have a flower growing out of the hind end.
Signature: Collins, VA
This insect is a Mayfly in the order Ephemeroptera. The flower is most likely just detritus that has accidentally stuck to the Mayfly, perhaps just after metamorphosis when the insect was softer and damp.
Letter 13 – Mystery Mayfly from Singapore
What is this bug?
Love the site… great fun for a fly tier like
myself! A friend from Singapore found many of the following insect on a resevoir there and wondered what is was… any ideas? Thanks!
This is some type of Homopteran, we believe. We are still checking though. Eric Eaton came to the rescue: ” Wondering now if the Homopteran from Singapore might actually be some kind of mayfly. Looks like it might have had two tails that broke off, and at least some mayflies have only one pair of wings, which this insect seems to have. Lastly, the fact that it was found by a fly fisherman floating in a reservoir just about seals the deal”
Hi guys… Hi there,
LOL, this is indeed a mayfly and not a Homopteran. This species has very short tail (not broken) but similar species up north (Malaysia and Thailand) do have longish tails. I have read elsewhere that identification is in order. This species burrow and feed on drift wood , the aquatic nymphs are favourite food for many types of fishes found in the reservoirs. I have seen the females ascending from sky in the morning and land on the water, and start fluttering (more like vibrating and sending ripples) its wing and dragging the egg sack attach via a strong silk like stuff to the end of the tail. It will keep fluttering until it attaches the egg sack to any structure dotting the shorelines and die there. The egg sag will absorb water and within days grow bulkier and look very much like frog eggs! Once the nymphs leave the clear jelly sack they start to look for drift wood to burrow and feed. Singapore is an seasonal country so this species lay eggs almost every morning with no particular peak season. I have been trying to find literature on this species to no avail for the last 2 decades. Save the short tail, they have very Mayfly like body anatomy (side fins along abs), which I therefore told my friends as much. That’s the story 🙂 Strangely I have yet to see the hatching and mating, only the spent stage as mentioned above. Where do you think I should look for the actions? I never see any shack so far! What a mystery Mayfly…. Regards,
Hi Yu Hock,
Thanks for all the valuable information on this unusual Mayfly. Sadly, we are unable to provide you with any additional information.
Letter 14 – Naiad might be immature Mayfly
Subject: Strange looking bug in ohio
Location: Mason, oh
May 1, 2014 5:28 pm
A friend was walking around in the woods in ohio and stumbled across this weird looking bug(?) it almost looks like a scorpion and frog bred. What is it?!
Letter 15 – Newly Metamorphosed Mayfly
May Fly Transformation
Here is a picture of some sort of may fly freshly coming out of its nymph shell. Found in the mountians of West Virginia. Thanks
Thanks for your image Jed, even though our posting is late.
Letter 16 – Small Squaregilled Mayfly
Subject: What is this bug?
Geographic location of the bug: Iowa
Time: 11:58 PM EDT
Your letter to the bugman: Can you please help identify this bug? it was trying to burrow into the siding on my house. Thanks!
How you want your letter signed: Thanks
This proved to be quite a challenge for us, but we eventually found this BugGuide image (which is eerily similar to your image) and this BugGuide image of a Small Squaregilled Mayfly in the genus Caenis. There is a nice image on Yobi Adventures. Mayflies have aquatic larvae and adults are generally found near bodies of water. We believe you were mistaken in your interpretation that it was trying to burrow into the siding of your house. Mayflies are popular bait for fly fishermen and many tied lures used by anglers are patterned after Mayflies.
Letter 17 – Spiny Crawler Mayfly Naiad
Subject: River bug
Location: Pacific Northwest USA
August 11, 2017 11:05 pm
Hi! I have been swimming in the Mohawk River in Marcola Oregon my entire life. I have never seen one of these little critters before. It was tiny. I caught it and released. Reminded me of a scorpion. It had fluttering fins(?) behind its legs. I am wondering if it is a larva or?
Signature: Johanna Leighty
The aquatic larvae of flying insects with incomplete metamorphosis including Dragonflies and Stoneflies are known collectively as naiads. We believe this is a Naiad of a Spiny Crawler Mayfly from the family Ephemerellidae based on this and other BugGuide images, but we are unable to provide a conclusive species identification. Here is another similar looking individual posted to BugGuide.
Letter 18 – Mayfly Naiad, not Stonefly Naiad
Mystery creature in creek
March 9, 2010
I was enjoying the lovely weather yesterday and took the opportunity to wade through our creek–after flipping some rocks over, I found this guy on the underside. It was probably 4 or 5 mm long. I’ve never seen anything like it, and was hoping you could shed some light on the mystery.
Thanks in advance! I just love the site.
Black Mountain, North Carolina
You have discovered the aquatic larva of a Stonefly, known as a naiad. We are linking to an image on BugGuide that was identified as being in the genus Acroneuria, but we are not certain if that is the same genus as your specimen. According to BugGuide: “nymphs are often found under large stones in streams and rivers” and “nymphs prey mainly on small aquatic invertebrates such as larvae of chironomids, mayflies, and caddisflies; detritus and algae are also eaten.”
Correction courtesy of Karl
Hi Daniel: This naiad appears to have three tails (cerci) not two, which would make it a mayfly. It looks lake a “clinger” mayfly (Ephemeroptera: Heptageniidae), possibly in the genus Maccaffertium. You could also check out Stenonema which look very similar, but most of the species in this genus have recently been moved to Maccaffertium or Stenacron. The Heptageniidae are well known to fly fishers and include the popular March Brown (Maccaffertium [=Stenonema] vicarium) and Cahills. Regards. K
Thanks for watching our back on this one Karl. We were in a rush this morning.
Letter 19 – Mayfly Naiads, not Stonefly Naiads
Bug on Wet Wood
January 23, 2010
We pulled a stick out of the river while camping at the Great Basin National Park, and there were these bugs all over the stick.
Great Basin National Park in Nevada
Thanks for sending us such detailed images of Stonefly Naiads. We are going to post all three of them because it is nice to have them clinging to their habitat.
According to the University of Kentucky Entomology website: “Stonefly naiads occur in fast moving streams where they are most commonly found clinging to the undersides of rocks. Many stonefly naiads are predators, feeding on other aquatic arthropods. Naiads of other species eat plants and algae. Although stonefly naiads were once very common in streams, they are very sensitive to pollution. These days, stonefly naiads are only common in very clean water. Stonefly adults can’t fly very well, and are usually found sitting on rocks near the streams where they emerged. Many stonefly adults do not feed, others feed on algae, pollen, or other plant parts. Stoneflies are a very important food source for fish and birds, and they are also eaten by spiders and predatory insects.”
Letter 20 – Small Western Green Drake: Drunella coloradensis
Subject: what is it
Location: western wa state
March 25, 2014 11:07 am
Found in western wa state
Are you able to provide any additional details? Was the sighting near water? This is obviously a nymph, and the front half of its body looks aquatic, while the rear end looks arboreal. We will attempt to discover this immature insect’s identity. It is going to have really big eyes.
Immediate Update: Small Western Green Drake
Hi again sonny. We quickly identified this Small Green Drake, Drunella coloradensis, on the Troutnut website. Here is a photo from BugGuide, which reports sightings in the Pacific Northwest, including Washington.