Mayflies and stoneflies are two fascinating aquatic insects that play crucial roles in the ecosystems of freshwater streams and rivers. Both of these insects serve as important bioindicators of water quality, as their presence or absence is a reliable indicator of a stream’s health.
In their nymph stages, mayflies and stoneflies contribute to the food chain by consuming algae, living plants, dead leaves, wood, and each other. Mayflies are known for their unique subimago stage in their metamorphic cycle, which is an active and mobile stage between the ultimate larval instar and the mature adult stage or imago. Stoneflies have a simple life cycle, starting as eggs, developing through the nymph stage, and eventually become adults.
Differences between mayfly and stonefly nymphs include factors such as their habitats and feeding behaviors. Mayflies are often found in fast-flowing streams and are considered nimble swimmers, while stoneflies prefer rocky environments and are known to be stronger crawlers. Understanding these insects and their similarities and differences will enable better insight into the ecological dynamics of freshwater environments.
Mayflies and Stoneflies: An Overview
Mayflies and stoneflies both have unique life cycles featuring aquatic nymph stages before they reach adulthood. Mayflies undergo a subimago stage between the ultimate larval instar and the mature adult stage, or imago1. Adult mayflies typically live for only a day, whereas stoneflies have longer adult lifespans.
Examples of life cycle stages:
- Mayflies: egg, nymph, subimago, imago (adult)
- Stoneflies: egg, nymph, adult
Mayfly adults are slender, soft-bodied insects with:
- Four membranous, extensively veined wings2
- Short antennae
- Large compound eyes
- Two long, threadlike cerci2
Stoneflies, on the other hand, have:
- Four membranous wings folded flat over the body
- Long antennae
- Two long cerci
Distribution and Habitat
Mayflies and stoneflies are found in various freshwater environments, and their presence or absence in a stream is a reliable indicator of water quality3. They typically prefer clean, well-oxygenated water, making them important indicators of ecosystem health. Regarding distribution, mayflies are commonly found in small streams4, while stoneflies can also be found in both streams and rivers.
- Indicator species for water quality
- Prefer clean, well-oxygenated water
- Sensitive to pollution
Ecological Roles and Importance
Both mayfly and stonefly nymphs play critical roles in the food chain:
- They consume algae, living plants, dead leaves, wood, and each other3
- They serve as an important food source for fish species, such as trout
Pros and Cons of Mayflies and Stoneflies:
- Pros: Indicator species for water quality, essential food source for fish
- Cons: Sensitive to pollution, high mortality rates
Aquatic Ecology and Water Quality
Importance in Food Web
Mayflies and stoneflies are essential components of aquatic ecosystems, particularly in streams and rivers. They play a vital role in the food web as they consume algae, living plants, and dead organic matter. In turn, they serve as food for larger predators, such as fish and birds.
For example, mayfly nymphs feed on algae, helping to maintain a balance of nutrients in the water. Similarly, stoneflies contribute to breaking down dead leaves and wood, recycling nutrients back into the ecosystem.
Indicator of Water Pollution
Aquatic insects like mayflies and stoneflies serve as bioindicators of water quality due to their sensitivity to pollution. The presence or absence of these organisms can signal changes in water quality, thus providing valuable information for environmental monitoring.
Here is a comparison table of mayflies and stoneflies:
|Located on abdomen
|Located on thorax
|Prefer slow-moving water
|Prefer fast-moving water
|Generally muted browns and greens
|Various, including brightly colored species
|Short, ephemeral adult stage
A decline in mayfly and stonefly populations can be an early warning sign of water pollution, such as increased sedimentation, pesticides, or nutrient imbalances. For instance, in Colorado, entomologists have documented concerns regarding pesticide contamination and its impact on mayflies and stoneflies.
In conclusion, understanding the role that mayflies and stoneflies play in aquatic ecosystems and their sensitivity to pollution is crucial for maintaining water quality and protecting these ecologically vital species.
Metamorphosis and Growth
Complete vs Incomplete Metamorphosis
- Complete Metamorphosis: This process includes four stages – egg, larva, pupa, and adult. Examples include midges and caddisflies.
- Pros: Offers specialization in different developmental stages; better adaptation to changing environments.
- Cons: Longer developmental period, more energy required.
- Incomplete Metamorphosis: Involves three stages – egg, nymph, and adult. Mayflies and stoneflies are examples.
- Pros: Shorter developmental time, less energy needed.
- Cons: Less specialization for different life stages; fewer adaptations to environmental changes.
|Egg, Larva, Pupa, Adult
|Specialization, better adaptation
|Longer period, more energy
|Egg, Nymph, Adult
|Shorter time, less energy
|Less specialization, fewer adaptations
- Mayflies: Larvae are known as nymphs, living underwater, and feeding primarily on algae. They undergo multiple molts before reaching the unique subimago stage in their metamorphic cycle.
- Stoneflies: Stonefly nymphs also live underwater, but feed on a wider range of organic materials. They go through several growth stages, shedding their exoskeleton each time.
Examples of different feeding habits:
- Mayfly nymphs: Primarily feed on algae
- Stonefly nymphs: Consume various organic materials such as leaves and microorganisms
Molt and Exuviae
- Mayflies: Mayflies molt multiple times, both as nymphs and during their winged subimago stage, which precedes the final imago (adult) stage.
- Stoneflies: Stonefly nymphs molt multiple times but do not have a winged subimago stage.
Fishermen find both mayfly and stonefly exuviae attractive as bait because it closely resembles the insects’ natural lifecycle transition stage. The fragile exoskeleton of the abdomen is an appealing target for fish.
Examples of molting stages:
- Mayflies: Nymphs, winged subimago
- Stoneflies: Only nymphs
Conservation Efforts and Environmental Impact
Threats to Mayflies and Stoneflies
- Loss of habitat
- Water pollution
- Temperature changes
- Invasive species
Mayflies and stoneflies are often considered “canaries of our streams” because their presence or absence indicates the water quality in a stream. They play a fundamental role in the food chain, consuming algae, living plants, dead leaves, wood, and each other in their nymph phase 1 . However, they face several threats, such as habitat loss, water pollution, sedimentation, temperature changes, and invasive species.
Protecting Water Quality and Habitats
Reducing Stormwater Runoff
- Planting native vegetation
- Installing riparian buffers
- Limiting impervious surfaces
One way to protect the habitats of mayflies and stoneflies is by managing stormwater runoff. By planting native vegetation, establishing riparian buffers, and limiting impervious surfaces, we can help improve water quality and reduce the negative effects of runoff.
Minimizing the Use of Fertilizers
- Conducting soil tests
- Using slow-release or organic fertilizers
- Applying fertilizers at the right time and in the right amount
Another important step in conserving mayfly and stonefly habitats is minimizing the use of fertilizers, which can contribute to water pollution and oxygen depletion. By conducting soil tests, choosing slow-release or organic fertilizers, and applying them at the right time and in the correct amount, we can help safeguard their habitats.
Supporting Environmental Laws and Conservation Organizations
- Complying with environmental regulations
- Participating in local conservation efforts
- Supporting organizations like the C.P. Gillette Museum of Arthropod Diversity
Lastly, supporting environmental laws and conservation organizations is crucial in the protection of mayflies, stoneflies, and their habitats. Ensuring compliance with environmental regulations, participating in local conservation efforts, and supporting organizations like the C.P. Gillette Museum of Arthropod Diversity can contribute to the preservation of these important species. Collecting insects and discovering new species, such as Kathroperla siskiyou, can help scientists study the effects of ecological changes on these organisms and provide valuable information for conservation initiatives.
|No subimago stage
|Depending on the species.
|Typically during the day
|Short-lived adult life (Few hours to two days)
|Longer adult life (a few weeks)
Fly Fishing and Entomology
Importance for Anglers
Anglers should have a basic understanding of entomology to improve their fly fishing success. Knowing the life cycles of mayflies and stoneflies can help determine the best fly patterns and imitations to use. Both insects are part of the order Ephemeroptera and are important for freshwater ecosystems, particularly as food for trouts.
Mayflies and stoneflies are more abundant in some regions like the East Coast. Their life cycles generally include molting and the exuviae stage, where they shed their skin.
Characteristics of Mayflies and Stoneflies:
- Mayflies: compound eyes, three cerci, swarm behavior, also known as shadfly
- Stoneflies: flattened body, strong swimming abilities, two cerci
Fly Patterns and Imitations
Fly patterns and imitations are crucial for effectively mimicking the adult stage of mayflies and stoneflies. They come in general and specific designs targeting various stages of insect life cycles. Dry fly patterns are especially popular among anglers.
Examples of popular fly patterns:
- For Mayflies: Pheasant Tail
- For Stoneflies: Stonefly Nymph
Comparison Table of Fly Patterns:
|Not as common
|Target specific species
|Target stage-specific patterns
Understanding the differences between mayflies and stoneflies allows anglers to choose the best fly patterns and imitations for their fly fishing experiences. Being aware of the nuances between these insects and the fly patterns available will ultimately enhance their fly fishing skills and increase their chances of a successful catch.
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 – Stoneflies
I have what appears to caddisflies all over my house. I have a large woods(over 100 acres) behind my house there is a stream 100 feets from my house and a pond about 100 yards from my house. There are thousands covering my house. Do you have any idea what to do with them. Unfortunately, Iam not a fly fisherman.
These are not Caddisflies, but Stoneflies, Order Plecoptera. We are baffled why, having a stream and a pond, you don’t fish. Your Stoneflies are seasonal and some years there are population explosions. Soon enough, they will be gone for another year.
Letter 2 – Stoneflies
June 4, 2010
I found the two of these up at my parents a couple of weeks ago. The female appears to be the larger of the two, with her abdomen/ thorax now curled up to the back side of her wings protecting eggs. The smaller is @ 1 1/4″ in length, the larger @ 1 1/2″ in length. Can you tell me what this is? Thank you.
These are Stoneflies in the order Plecoptera. According to BugGuide in a posting with an aversion to punctuation: “nymphs occur primarily under stones in cool unpolluted streams; some species occur along rocky shores of cold lakes, in cracks of submerged logs, and debris that accumulates around stones, branches, and water diversion grills spring and summer adults may be found resting on stones and logs in the water, or on leaves and trunks of trees and shrubs near water; winter stoneflies are often attracted to concrete bridges over streams, and some species are commonly found on snow or resting on fence posts during the warmer days of late winter“.
Letter 3 – Stoneflies
type of bug
April 1, 2011 4:58 pm
Can you tell me what kind of bug these are? They are many of them on the side of my house.
These are harmless Stoneflies. They have aquatic larvae that live in freshwater streams, and they cannot tolerate polluted conditions. In your case, they indicated that there is probably a nearby stream that has not been contaminated by pollutants.
Letter 4 – Stonefly
I found this bug, would love to know what it is
Tue, Jun 2, 2009 at 12:53 PM
Me and the kids stopped off by a mountain stream at the bottom of helvellyn in the lake district on sunday and there were lots of these creatures on the rocks around the water, i would appriciate your help in finding out what type of “thing” it is – it resembled something like a flat grass hopper/ over grown earwig crossed with a scorpion, it didnt have a sting but had quite large mouth/biting bit – ithey were a good 2″ long and not particualrly friendly looking
This is the aquatic nymph of the Giant Stonefly known as a naiad. Presumably it has crawled from the stream, will soon molt its exoskeleton, and become a winged adult. Adult Giant Stoneflies do not feed, but are relished by trout, other fish, birds and many riparian predators. Anglers use both larval and adult Giant Stoneflies as bait. We have recently posted a photo of an adult Giant Stonefly for comparison. You photo and letter will not go live on our site until Tuesday at noon. We have been preparing posts to update one a day while we are out of the office planting tomatoes.
Letter 5 – Stonefly
beetle with stainedglass wings
June 6, 2010
Hi, We found this beetle hanging out on our newly built workshop. He was on the underside of the eaves. Very elegant wing patterns. Thanks for any clues on what this might be.
This is not a beetle, but a Stonefly, a member of the order Plecoptera. They are generally found near sources of water.
Letter 6 – Stonefly
Location: Taiki-cho, Hokkaido, Japan
March 22, 2012 3:02 am
I live in eastern Hokkaido, Japan, in a small farming village. The other day I found some bugs I had never seen before in my bathtub, and then, when I left my apartment, saw literally hundreds on my apartment’s walls and windows! I have never seen these bugs before, and I’ve lived in Japan for over 3 years now (and I’ve even encountered Asian giant hornets!) This was the best picture I could take of them. They are over 1cm long.
If you could help me out that would be great!
Just because there is a large population of an insect does not mean it is an infestation or some other bad portent. This is a Stonefly and the larvae or naiads of Stoneflies are aquatic insects that can only survive in unpolluted running water like streams and brooks. The fact that there is a large population of Stoneflies is an indication that the water in your area is relatively pure, so take this spring swarm as a good sign.
Letter 7 – Stonefly
Subject: what’s this bug?
Location: Hastings, Michigan
June 4, 2014 12:44 am
When i found this bug a friend told me about your site. Looks cool!
Signature: this bug jumped up on my lap in Hastings, MO
This is a Stonefly in the order Plectoptera.
Letter 8 – Stonefly
Subject: Termite or something else?
Location: Northern Iowa
July 30, 2015 6:48 am
I have found many of these bugs inside the house over the past week. We just moved into the house a few weeks ago. We live in northern Iowa in a town where apparently there are no termites… But these bugs look exactly like termites. I have researched online and cannot find any other bug it resembles.
Thanks to this image on BugGuide, we believe we have correctly identified your Stonefly as a member of the genus Perlesta. Stoneflies have aquatic nymphs, so we are guessing you live near some body of water. Like other aquatic insects, Stoneflies frequently are part of a mass emergence of 1000s of individuals, and some species may be attracted to lights, which is why you are currently finding them in the home. The emergence will not last long and you will probably have them vanish in the near future. Though this may be a temporary nuisance, Stonefly larvae cannot live in polluted waters, so you can be comforted that your local water supply is clean.
Letter 9 – Stonefly
Subject: Please help with ID
Location: Rhode Island, USA
April 4, 2016 8:24 am
I found about ten of these clinging to the outside of my house at the end of February (unseasonably warm day). Can you help identify?
This is a harmless Stonefly. They are generally found not far from a stream or river. Additionally, according to BugGuide: “nymphs of most spp. develop in cool, well-oxygenated water and do not tolerate pollution; therefore, their presence is an indicator of good water quality, and their absence in areas where they previously occurred may indicate pollution.”
Thank you very much Daniel. I do indeed live by a river.
Letter 10 – Stonefly
Subject: pictures of bug upon awakening….
Location: Fredericksburg Va
May 19, 2017 11:31 pm
This bug was on my pillow on Wednesday the 5th of May….a bit after a biblical 3 days straight downpour in Fredericksburg Virginia…It was on my pillow above my ear ……………………..
I think it was bigger than an an inch but smaller than an inch and a half.
I’d really like to know what it was…………
Signature: susan warner
This is some species of Stonefly in the order Plectoptera. We wish you had been able to attach an in focus image of the entire insect as that would help us with identification. This BugGuide image of a member of the genus Isoperia, and this BugGuide image of Taenionema atlanticum both look similar to your individual. Do you live near a stream or river? The larvae of Stoneflies are aquatic, and they are f0und in fresh water.
the photo in BugGuide looks exactly like the fellow on my pillow….thanx. I live near the Rappahanock River hence a freshwater source. I have hand tremors and now have real trouble getting a well focused photograph…. but now it’s hard to get an in focus shot. Curses!
Letter 11 – Stonefly
Subject: Fish fly?
May 30, 2017 9:49 pm
I’ve found 3 of these in the last 3 days in my home and am wondering what they are. They’re roughly 2.5″ black and gray with multiple sets of wings. They’re quite loud when they fly and quick on their feet. I do live next to a river and have seen them outside but this is the first time I’ve seen them in my home.
This is not a Fishfly. It looks more to us like a Stonefly, another insect with an aquatic nymph that is found near water.
Letter 12 – Stonefly
Subject: Can someone ID this?
Geographic location of the bug: Pennsylvania
Time: 12:42 PM EDT
Your letter to the bugman: I found one in a bedroom closet, and another on my patio. Please help! I need to know what this is.
How you want your letter signed: Samantha
Do you live near a body of water? This is a Stonefly, an insect with an aquatic larval form. It is harmless. We surmise it accidentally found its way into your closet. Here is a BugGuide image for comparison.
Letter 13 – Stonefly Exoskeleton
What is it?
I took a pic of an insect that appears to be skeletal remains that had been on a rock near a river. I have no idea what type of bug it is. I used a super macro shot on it. The actual size is about 1/2". Looking forward to hearing from you,
This is the exoskeleton of a Stonefly. The larvae are known as naiads and they are aquatic.
Letter 14 – Stonefly Exuvia
Subject: The bug in your drawing
Location: Bank of Clearwater River Kamiah ID
October 27, 2012 12:48 am
I took photos of several of these exoskeletons (at least I am assuming that is what they are) on rocks by the Clearwater River near Kamiah Idaho last week (mid-Oct.). When I opened up your website I was so excited, because there was a drawing of this creature. But it doesn’t tell me what it is. I’ve searched your lists (not all, but many) and can’t find it either. Can you help me scratch the buggy itch in my brain? Thanks!
The bug in the drawing is an Earwig, but this is the exuvia of a Stonefly naiad.
Letter 15 – Stonefly Exuvia
Location: Red Deer, Alberta, Canada
February 9, 2014 11:48 am
In April 2013, we were sitting under a bridge by the river, when we noticed these guys all over the wall. They were about 5 cm long and didn’t move much (we however found we moved very quickly).
Signature: with love, confusion and the heebie jeebies
This is the exuvia of a Stonefly, a flying insect that spends its immature development as an aquatic naiad. When maturity approaches, the naiad leaves the water and molts for the last time, emerging as a winged adult Stonefly. Here is an image of a similar looking Stonefly Exuvia from BugGuide.
Letter 16 – Stonefly Exuvia from Scotland
Subject: What bug is this?
Location: Bracklinn Falls, Callander, Scotland, UK
May 27, 2017 6:35 am
My friend saw this bug while out walking and was wondering what exactly it is. I think it looks like some sort of earwig or mantis but I honestly have no idea. It has six legs, medium-long antenna at the back and short ones at the front, black and white with stripes on its back and it doesn’t appear to have wings. It’s currently Summer and I believe it was around the Bracklinn Falls area in Callander.
Signature: Lauren Pearson
We are surmising that Bracklinn Falls means a waterfall on a stream or river. This is the exuvia or cast-off exoskeleton of a Stonefly, an aquatic nymph that eventually develops into a winged adult. Here is a FlickR image of a Scottish Stonefly nymph and here is an image of an adult Stonefly from Encyclopedia of Life.
Letter 17 – Stonefly Exuviae
Subject: Strange bug
Location: Maine USA
May 28, 2016 7:00 am
My friend took pictures of these bugs and we cannot figure out what they are.
Signature: Emil Falkenberry
These are the Exuviae or cast off exoskeletons of aquatic nymphs of Stoneflies, known as a naiads, so we are guessing these images were taken close to a stream or river. Of the Stonefly family, BugGuide notes: ”
nymphs occur primarily under stones in cool unpolluted streams; some species occur along rocky shores of cold lakes, in cracks of submerged logs, and debris that accumulates around stones, branches, and water diversion grills. spring and summer adults may be found resting on stones and logs in the water, or on leaves and trunks of trees and shrubs near water; winter stoneflies are often attracted to concrete bridges over streams, and some species are commonly found on snow or resting on fence posts during the warmer days of late winter.” Though we cannot be certain of the species, your images resemble the Exuviae of the Beautiful Stone, Paragnetina immarginata, which is pictured on BugGuide. Since one of your images appears to be up-side-down, we are guessing they may have been taken on a bridge overhang.
Thank you so much and yes they were under a bridge by water. 🙂 Have a great weekend.
Letter 18 – Stonefly Exuviae
Subject: Found dozens dead by the river
Geographic location of the bug: Western Massachusetts
Time: 08:45 AM EDT
Your letter to the bugman: Hello bugman-
I was walking by the river this morning and found dozens of these bugs dead on small rocks. I cannot identify them. Do you know what they are? And is it normal to come across what seems like a mass death? Thanks for any insight you can provide and keep up the amazing work!
How you want your letter signed: Best wishes, Lucy
These are not dead insects. They are the exuviae or shed exoskeletons of Stonefly naiads. The aquatic larvae of Stonflies are aquatic, and when they approach maturity, they climb out of the water and molt for the final time, emerging as winged adults. You did not encounter a “mass death” but rather, evidence of a mass emergence.
Letter 19 – Stonefly from Patagonia, Chile
Subject: An insect that we have not seen on our land in Chilean Patagonia before
Location: La Junta, Aisen, Chile
April 12, 2015 3:34 pm
This insect landed on a volunteers arm while she was working away on our small farm in northern Aisen, Patagonia. We have never seen it before and wonder what it is? In adavance thanks for the work that you do, it has enabled us to better understand our ecosystem.
Signature: Paul Coleman
This is a Stonefly in the order Plecoptera, a species generally found near water as the larvae are aquatic nymphs. According to BugGuide: “nymphs of most spp. develop in cool, well-oxygenated water and do not tolerate pollution; therefore, their presence is an indicator of good water quality, and their absence in areas where they previously occurred may indicate pollution.”
Letter 20 – Stonefly from the Philippines
July 27, 2016 12:06 am
hi just want to clarify if this is a stonefly (Order: Plecoptera)? how long will it take for the eggs to hatch? Thanks;)
Sorry for the long delay. This identification has been on our back burner for nearly two weeks. We agree that this is a Stonefly in the order Plecoptera. Though it is a North American species, this individual from BugGuide looks very similar to your Stonefly.
Letter 21 – Stonefly from UK
Subject: Help me identify
Location: 54° 55′ 59.99″ N, 2° 58′ 59.99″ W
May 29, 2016 5:50 am
Hi. When I was walking i found this what i believe to be a type of stonefly but couldn’t identify it. Could you please tell me what it is? The insect was with what i guess was it’s mate foraging for food. They were beside an estuary where they occasionally were flying off then returning. The insects averagely were about 7 cm within length. The Picture Should have sent with this e-mail, The Geographical location is estimated but i hope the location should help Thanks.
Signature: Yours Scincirley
We agree that this is a Stonefly in the order Plecoptera. We have determined that your global coordinates are in the UK. This appears to be a flightless species as the wings do not look long enough to allow flying. Alas, we have been unable to locate any matching Stoneflies online.
Letter 22 – Stonefly Naiad
What is this – Bug, Crayfish, ???
Location: Woodstock, NY
April 9, 2011 11:43 am
I live in Woodstock, NY on a lake with a stream. In pools around the stream there are 1000s of these of various sizes. They also seem to be undergoing a metamorphosis. Some are inside cocoons made of various elements. They are in the water, mostly, but seem to be able to survive on land.
Signature: Alan Cohen
This is the larva of a Stonefly, known as a Naiad. Their presence in large numbers is a good indication that the stream in which they were found has very low levels of pollution. You can find additional information on Stoneflies on BugGuide.