Stone Fly Life Cycle: A Quick Guide to These Aquatic Insects

Stoneflies are fascinating insects known for their unique life cycle. As a crucial part of various ecosystems, understanding their life cycle can provide valuable insights into the health of the environment. We’ll explore the key stages of a stonefly’s life and how they metamorphose from nymphs to fully grown adult insects.

In the beginning of their life, stoneflies start as eggs. Female stoneflies lay their eggs in fresh water, where the nymphs will spend most of their lives. This aquatic stage is crucial, as it offers the developing insects a safe haven and a food source. You’ll find that stonefly nymphs are well-adapted to their watery surroundings, with an elongated body shape and flattened legs to help them swim and navigate the underwater terrain.

As they continue to grow, stonefly nymphs go through a series of molting events, shedding their exoskeleton to accommodate their increasing size. Once they reach maturity after a varying number of molts, these nymphs will finally emerge from the water and transform into adult stoneflies. The breathtaking moment when stoneflies take flight and venture into the terrestrial world marks the end of their remarkable metamorphosis.

Understanding Stoneflies

Stoneflies belong to the order Plecoptera and are aquatic insects known for their unique life cycle. They get their common name due to the fact that their immature forms, or nymphs, usually live on or around stones in streams and rivers 1. These insects come in various genera and families, with a wide range of species found across the globe.

To give you an idea about their appearance, stoneflies often have dull, dark, and drab brown, yellow, or sometimes green colors 2. A distinctive feature of these insects is their antennae, which are threadlike and long.

The term “Plecoptera” is derived from Greek words, meaning “braided wings.” This name is due to the adult stoneflies’ wings, which are clear, membranous, and finely veined 2. They have two pairs of wings that rest closely down the back of their body, with forewings covering the hindwings.

In their life cycle, stonefly nymphs undergo several stages of growth before becoming adults. They typically inhabit clean, fast-moving freshwaters, making them sensitive to changes in water quality and temperature 3. This sensitivity can serve as an indicator of ecosystem health.

Here are some key features of stoneflies:

  • Aquatic insects from the order Plecoptera
  • Known for living on or around stones in streams and rivers
  • Wide range of species found globally
  • Long, threadlike antennae
  • Two pairs of clear, membranous wings in adults
  • Sensitive to changes in water quality and temperature

Understanding the life cycle of stoneflies can help you appreciate the delicate balance that these insects maintain with their environment. By being aware of their habitat and ecological role, you can better understand the significance of preserving clean water sources and protecting these unique creatures.

Habitats of Stoneflies

Stoneflies are fascinating insects that rely on specific environments to complete their life cycle. In this section, you will learn about their preferred habitats and the factors that determine where they can be found.

Stoneflies spend most of their life as larvae in aquatic environments, specifically in rivers and streams with clean and fast-moving water. These insects thrive in areas with high-quality water, since they are highly sensitive to pollution. It is common to find stoneflies living among rocks, giving them a stable place to rest and hide from predators.

For example, many stonefly species can be found in the Appalachian region, where they rely on cold perennial streams for their survival. However, some species have also adapted to living in intermittent streams, which experience reduced or lack of flow during certain seasons. In a study conducted at Mammoth Cave National Park, differences in stonefly assemblage composition and distribution were observed based on stream permanence.

Stoneflies are not only important as indicators of water quality, but they also play a crucial role in the food chain of their habitats. In their larval stage, they consume algae, living plants, dead leaves, wood, and sometimes other insects. As a result, they are an essential food source for animals further up the food chain, such as fish and birds.

To summarize, the preferred habitats of stoneflies include:

  • Rivers and streams with clean, fast-moving water
  • Areas with high water quality and low pollution levels
  • Rocky environments that provide shelter and stability

By understanding the unique habitat requirements of stoneflies, you can appreciate their important role in maintaining healthy river and stream ecosystems.

Stonefly Life Cycle

The life cycle of a stonefly begins with the female laying eggs in the water. They can be laid in various ways, such as in flight or on nearby vegetation source. Once the eggs are in the water, they eventually hatch into small aquatic larvae called nymphs.

As stonefly nymphs, these creatures live underwater for about 1 to 2 years, depending on the species source. During this time, they’ll grow and molt, shedding their exoskeletons multiple times, and in the process, growing larger.

The nymphs continue to grow until they reach their final larval stage. At this point, they crawl out of the water, typically onto stones (hence the name “stonefly”), and emerge as winged adults after one final molt source. The adult stoneflies live only for a short time compared to their life as nymphs, typically a few weeks, mating and laying eggs to complete the life cycle.

Stoneflies can be found year-round, but the exact timing of their life stages depends on the species and their specific environmental conditions source. The season when they primarily emerge as adults may also differ among species.

Physical Characteristics of Stoneflies

Stoneflies are insects with unique physical features. They have a robust exoskeleton that provides protection and support for their body. Their body is typically divided into three main parts: head, thorax, and abdomen. Here are some notable characteristics of stoneflies:

  • Their color varies, but it usually ranges between brown, black, and yellow shades. This helps them blend in with their surroundings.
  • Stoneflies come in various sizes, from a few millimeters to several centimeters long. The larger ones are generally found in North and South America.
  • They have deep, compound eyes that enable them to detect movement and light effectively. This feature helps them avoid predators and locate prey.

Stoneflies’ abdomen comprises several segments, usually with two slender tail filaments extending from the last segment. These filaments can aid them in staying stable while they swim or crawl in their aquatic habitats. Some species possess enlarged gills on their abdominal segments, allowing for better oxygen absorption underwater.

Overall, stonefly physical characteristics are diverse, with each species adapted to its particular environment. These unique traits contribute to their survival in a variety of ecosystems across the globe.

Behavioral Attributes

Stoneflies exhibit a range of interesting behaviors throughout their life cycle. In this section, you’ll learn about their behaviors in different stages, such as living in the subsurface, behavioral drift, and nocturnal activities.

Stoneflies typically live in the subsurface of clean, swift-flowing streams and rivers. They spend most of their lives underwater. As they grow and develop, these insects go through behavioral drift. This process involves the dislodging and drifting of immature stages due to the current and other environmental factors. Here are some factors that influence their drift:

  • Water current strength
  • Habitat disturbance
  • Availability of food

During the night, stoneflies become nocturnal, actively moving around to search for food and avoid predators. This behavior is more prominent in males than in females.

Mating behavior in stoneflies is unique, too. Males and females participate in a mating dance to attract their partners. When a female is ready to mate, she releases pheromones to signal her readiness. These are some features of their mating behavior:

  • Males drum on rocks and vegetation to attract females.
  • Females respond by drumming back, creating a rhythmic communication.
  • They mate on stones, vegetation, or other surfaces near the water.

Pay attention to these key characteristics of stonefly behavior in their life cycle:

  • Living primarily in the subsurface of freshwater ecosystems
  • Experiencing behavioral drift during development
  • Exhibiting nocturnal activity, especially in males
  • Engaging in unique mating rituals involving communication through drumming

By understanding these behavioral attributes, you can better appreciate the fascinating life cycle of stoneflies in their natural habitats.

Stoneflies and Fishing

Stoneflies play a crucial role in the aquatic food chain as they consume algae, living plants, dead leaves, wood, and even each other in their nymph phase. This makes them an important food source for many animals further up the food chain, including fish like trout.

When you’re out on the river, you’ll notice that stoneflies are frequently used by anglers as bait for trout. That’s because trout are instinctively drawn to the drifting nature of these insects. As such, many fishing enthusiasts use stonefly imitations like dry flies to successfully attract trout.

Stoneflies are a great choice for anglers because:

  • They are a part of the trout’s natural diet, making them more effective as bait.
  • Stonefly imitations, like dry flies, can effectively mimic the drifting action of real stoneflies, enticing the fish to strike.

Keep in mind that stoneflies and mayflies are often seasonal, with their populations typically thriving during specific times. As a result, fishing with stonefly imitations can be more effective during these periods.

To boost your fishing game, it’s essential to pay attention to the life cycle of stoneflies and their role in the ecosystem. Properly utilizing this knowledge can improve your chances of catching prized trout. Remember to keep your eye on local hatches and familiarize yourself with the variety of stonefly species to make the most of your fishing experience.

Types of Stoneflies


Mayflies are one of the most common types of stoneflies. They belong to the order Ephemeroptera. These insects have a short lifespan, typically just a few days, which is why they’re called “mayflies.” Some key features of mayflies include:

  • Delicate, clear, membranous wings
  • Long, threadlike antennae
  • Dull, dark colors like brown, yellow, or green

Mayflies can be found in and around streams and rivers where they feed on organic matter and serve as a vital food source for various fish and other aquatic life. Their presence can also be used as an indicator of clean water and a healthy ecosystem.

Winter Stoneflies

Winter stoneflies belong to the families Capniidae and Taeniopterygidae. As their name suggests, these stoneflies are unique because they are mostly active in the colder months. Here are some key features of winter stoneflies:

  • Small size, typically 5-12mm long
  • Dark-colored wings that are held flat over their body
  • Relatively short antennae compared to other stoneflies

These insects also play an important role in aquatic ecosystems, often indicating good water quality, as they are sensitive to pollution.


Salmonflies belong to the family of stoneflies known as Pteronarcyidae, with Pteronarcys dorsata being a common species. They are large, impressive insects that can provide a food source for many organisms, including fish like salmon. Their most distinctive characteristics include:

  • Robust body, reaching up to 50mm in length
  • Relatively short antennae
  • Dark brown to black coloration with white or yellow patterns on their wings

These stoneflies prefer fast-flowing, cold waters of rivers and streams where their nymphs can develop.

Golden Stones

Golden stones, or perlids, are an important group of stoneflies belonging to the family Perlidae. They tend to be medium-sized, with a few distinct features:

  • Bright golden-brown coloration
  • Slender, elongated bodies
  • Two long, needle-like tails called cerci

Golden stones are found in and around clean, fast-flowing streams and rivers. They contribute to their ecosystem by serving as both predators and prey.

Yellow Sally

The Yellow Sally stonefly, part of the family Chloroperlidae, is known for its striking yellow color. Here are some highlights of this stonefly’s characteristics:

  • Bright yellow-orange color
  • Small to medium size, usually around 10-15mm long
  • Slender body structure

These insects can be found in small streams and rivers, providing both food for various organisms and serving essential roles in their ecosystem.

Importance of Stoneflies in Ecosystem

Stoneflies play a crucial role in the ecosystem, especially in freshwater habitats. These aquatic insects are sensitive to their environment and can help indicate the quality of the water. They require clean, fast-moving water with abundant dissolved oxygen for their survival and development. When you find stoneflies in a stream, it typically means the water is relatively free of pollution.

These insects breathe through gills on their abdomen, which depend on the oxygen levels in the water. Due to their sensitivity to oxygen levels and water quality, they are considered vulnerable to pollution. Consequently, they are often used as biological indicators of overall stream health.

In addition to their role as water quality indicators, stoneflies are an essential food source for various predators in the ecosystem, such as fish and birds. Their presence helps support a diverse and healthy environment. Furthermore, they contribute to energy flow and nutrient cycling within these ecosystems.

When it comes to vegetation, stoneflies don’t have a direct impact on plants or pollen. However, they do indirectly contribute to the nutrient cycling in aquatic habitats, which in turn may influence the growth of vegetation nearby. Aquatic plants benefit from the nutrients released by stoneflies and other organisms in the water, promoting a balanced ecosystem where plants, animals, and insects coexist.

In summary, stoneflies are essential to the ecosystem for several reasons:

  • Indicating water quality and pollution levels
  • Providing food for predators
  • Contributing to energy flow and nutrient cycling
  • Supporting healthy aquatic habitats and indirectly influencing vegetation growth

So, the next time you come across a stonefly, remember that these insects play a vital role in maintaining a balanced and healthy ecosystem.

Stoneflies Distribution

Did you know that stoneflies are found in various parts of the world, including Montana? These fascinating insects make their homes in freshwater rivers, streams, and even sometimes lakes. You’ll mostly find them in colder regions or areas with high water quality, as they are sensitive to polluted water.

In the western regions, such as Montana, the distribution of stoneflies is widespread. Here are some features of their distribution in this area:

  • They thrive in mountainous regions of Montana, where there is an abundance of clean, cold water sources.
  • Their distribution tends to be more diverse in the western parts of the state compared to the eastern parts.

Stoneflies in Montana and the West have a fascinating life cycle, starting as aquatic larvae that eventually metamorphose into winged adults. Along with this, their unique characteristics make them valuable indicators of water quality and crucial players in aquatic ecosystems.

Some key characteristics of stoneflies include:

  • They have long, threadlike antennae.
  • Their wings are clear, membranous, and finely veined.
  • Stoneflies are generally dull, dark, or drab in color.

So when you’re exploring rivers and streams in Montana or any other western region, keep an eye out for stoneflies. They are a true testament to the health and vibrancy of the aquatic ecosystems in which they live. Always remember to treat these delicate habitats with care, and ensure the continued thriving distribution of these fascinating insects.

Life Span of Stoneflies

Stoneflies have a unique life cycle that can vary depending on the species. They begin their lives as aquatic larvae and eventually molt to become winged adults. Their life spans underwater as immature larvae can last for 1 or 2 years.

During winter and early spring, you might observe adult stoneflies emerging from their aquatic environments. This is due to the fact that they are one of the few insect groups that have their adult stage during these colder seasons, as mentioned in this resource.

Stoneflies reside in various stream types and thermal regimes. It’s important to note that climate change has the potential to affect their habitats and life spans. Increasing temperatures and changes in water flow can result in physiological stress and reduced populations for these insects.

Here’s a brief summary of their life cycle across different seasons:

  • Spring: Larvae continue to grow in the streams while some adult stoneflies emerge.
  • Summer: As temperatures rise, stoneflies may experience changes in their environment affecting their survival.
  • Winter: Adult stoneflies are more typically observed during this season.

Adult stoneflies have a terrestrial stage that lasts only a few weeks. During this time, they focus on mating and laying eggs back in the aquatic environment before they die. This is crucial for the continuation of their species, and understanding their life span can help with conservation efforts, such as the meltwater stonefly, which is listed as threatened under the Endangered Species Act.

By knowing this information, you can better appreciate the unique life cycle and lifespan of stoneflies and their role in the ecosystem.

Reader Emails

Over the years, our website, 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 – Stonefly??


Good morning,
I’ve had a keckuva time identifying this insect I saw yesterday (February 29) in hordes flying above a freshwater creek in Maryland. Any idea? Sorry it’s a blurry picture, it’s the best I could do. The insect has two dark bands. They were doing lots of flying and appeared to be dropping into the water from above and then skittering across the surface of the water by flapping their wings. They were about 3/4" not including their antennae.
Thanks a lot!

Dear Vicki,
I believe you are absolutely right in your identification of a Stonefly, Plecoptera species. There are some 200 species of Stoneflies. Often adults appear in great numbers in the spring. They are poor fliers and are seldom found far from water. They lay their eggs in the water and the nymphs are aquatic. Thank you for providing a photo of our first stonefly for a new page.

Dear Daniel,
Thanks so much for writing back! You have a great web site and I’ve really enjoyed it. With 200 species of stoneflies, you could see how I needed an expert eye. I saw the flies while kayaking on Tuckahoe Creek on the Eastern Shore of Maryland. The highlight of my day, though (other than seeing an otter) was finding a cocoon of a Polyphemus Moth, which I took a picture of and left to dangle patiently on its limb for a few more months.
Thanks very much again!

Letter 2 – Winter Stonefly


Subject: They’re everywhere!
Location: Central PA
March 28, 2014 12:41 pm
There are at least a dozen of these bugs hanging out on my front porch.. and they love to hitch a ride indoors by falling/jumping onto my clothes as I walk through the door. What are they?
Signature: Randi

Winter Stonefly

Dear Randi,
This is a Stonefly in the order Plecoptera, and it looks very similar to the Winter Stonefly in the genus
Taeniopteryx that is pictured on BugGuide.  The nymphs are aquatic, and 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,” so you must have clean, unpolluted water nearby.

Letter 3 – Stonefly Naiad


Subject: What is This?
Location: Tracy, New Brunswick, Canada
August 13, 2012 2:26 pm
Good day Bugman.
I found this little guy in the bottom of a bucket at our camp on the weekend. Could you tell me what he is? It looks alien 🙂
Signature: C. A. Brown

Stonefly Naiad

Dear C.A. Brown,
This is the Naiad of a Stonefly.  A Naiad is an aquatic larva that eventually becomes a winged adult.  We cannot tell you the exact family, but this Naiad somewhat resembles this Common Stonefly Naiad from BugGuide.

Letter 4 – Stonefly Naiad


Subject: Water Scorpion?
Location: Germantown, Ohio
October 19, 2016 3:49 pm
I found this dude in the creek today while fossil hunting. I picked up a piece of granite from the water and there he was. I believe he’s some some of sediment deposit feeder as I saw him eating dirt off the rock. I took a few pictures and a video and set him back in the water. Let me know what you think!
Signature: Carly W

Stonefly Naiad
Stonefly Naiad

Dear Carly,
This looks like the aquatic larva of a Stonefly, known as a naiad.  Compare your individual to this individual posted to BugGuide.

Letter 5 – Stonefly Naiad


Subject: South BC bug, similar to the insect image on your website
Location: South BC
August 19, 2017 6:29 am
Hi there Bugman,
My mate found this insect in the river in south BC.
I’ve been looking everywhere online to find out what this insect is. Not much result! However, the closest thing that has come up is the picture on your website right under “TOP TEN” on the left side bar.
Could you please tell us what it is?
Thanks mucho and much bug love!
Signature: Bugman

Stonefly Naiad

The image on our homepage is an Earwig, and though your creature shares some similarities, they are not closely related.  Your insect is an aquatic nymph, the naiad of a Stonefly.   Your individual looks very similar to this BugGuide image submitted from Alberta, Canada.

Letter 6 – Stonefly shed skin


what is this bug/water beetle and this shed husk?
I found these in Arizona in the Pinetop-Lakeside area. Thanks,
glen b.

Hi Glen,
This is the shed skin of a Stonefly naiad left after it crawled out of the water and began life as a winged adult.

Letter 7 – Welsh Stonefly


What is this bug?
Dear Bugman,
I am really impressed with your swift reply and you certainly have helped. Here is my next mystery – well not for you probably but certainly for a novice like me. Found near the pond, well originally on a pond leaf. I am wondering is it a stonefly as it seems to have many of the characteristics of the stonefly nymph which are numerous in our pond.
Diolch yn fawr
Thank you
Cynon Valley, South Wales

Hi again Mary,
Sure looks like a Stonefly to us. They belong to the order Plecoptera and are generally found near rapidly running streams or wave-washed lakes. Perhaps your European species favor calmer waters. The naiads are common under stones, hence the common name.

Letter 8 – What’s That Exuvia??? A Stonefly


Subject: Strange bug.
Location: Deer Park, Washington
May 18, 2014 9:35 pm
I personally have not seen this bug, but I just recently had a friend describe how his family and himself found a ton of these hanging out by their parents house in Clayton Washington. He described it to me, saying that he was actually quite a bit scared about it. While I thought his mysterious bug was interesting, I more or less brushed it off. Then this afternoon, I had several friends talk about some weird bug they saw and one actually posted a picture of it (picture I included). I know absolutely nothing about the bug other than it’s in eastern Washington, was chilling outside, and that it’s freakier than a Parlomont bassline. Help would be much appreciated.
Signature: Eric

What's That Exuvia
Stonefly Exuvia

Hi Eric,
This is the exuvia or cast off exoskeleton of an insect that has undergone metamorphosis.  We believe it is a member of the order Orthoptera.  We will do additional research and attempt to identify the species.

Thanks to several comments, we realize that this is actually a Stonefly Exuvia from the order Plecoptera.  Immature Stoneflies or Naiads are aquatic insects that mature into winged Stoneflies, so the exuvia are generally found in close proximity to bodies of water.

Letter 9 – Winter Stonefly


please help
Location: northern maryland
January 19, 2012 11:15 am
I live in northern maryland in hagerstown its currently winter time in january but its been kind of mild. We have some kindof warm days for winter and I keep finding these bugs on my porch. Was just wondering what kind of bugs these are and if it is something on my porch attracting them. Please and thanks in advance.
Signature: Laura

Winter Stonefly

Hi Laura,
This benign creature is a Winter Stonefly, and they are never found far from sources of pure, unpolluted streams.  We will elaborate on this when we have an opportunity.  See BugGuide for additional information.

Letter 10 – Winter Stonefly


Subject: First insect of spring
Location: Riverbend Park, Virginia
March 9, 2015 4:23 pm
Hello, while walking along the Potomac River today, we saw this insect in fair abundance. It appears the American Coots and other waterfowl were eating them from the surface of the river. They were also landing on people, trees, and the still snowy ground. As far as I know, the first sighting of them was yesterday. Average length was 0.75 inches. Do you know what this insect is? Thank you!
Signature: Seth

Winter Stonefly
Winter Stonefly

Dear Seth,
This is a Winter Stonefly in the family Taeniopterygidae.  According to BugGuide:  “The defining need of winter stonefly nymphs is for very high levels of oxygen in the water. Warm temperatures, excessive organic matter, and many pollutants all reduce oxygen levels. The result: they’re only active in the coldest part of the year and are very sensitive to pollution.  Their main interest to humans is as an indicator species: you can tell that water is unpolluted if stoneflies live there. They also provide food for trout – though not as much as species active when trout are themselves more active in warmer parts of the year.”
  Here is an image of a member of the genus Taeniopteryx from BugGuide that looks very similar.

Letter 11 – Winter Stonefly


Subject: Insect ID
Location: Southern NH
April 5, 2017 4:08 pm
HI, I’ve been seeing these little insects in my house…can you tell me what it is? Thanks
Signature: Kitty

Winter Stonefly

Dear Kitty,
Congratulations on having a population of Winter Stoneflies at your house because it is our understanding that the aquatic nymphs can only survive in clean, unpolluted water.  According to BugGuide:  “adults emerge from November to June (most common in winter and early spring).”


  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

6 thoughts on “Stone Fly Life Cycle: A Quick Guide to These Aquatic Insects”

    • Thanks for that comment. We must have been tired and not thinking clearly this morning when we looked at the image.

  1. These things have invaded my home! Not sure where they are getting in, but I probably remove 3 or 4 every day. Some are larger than others. They do no harm, but I wish they’d stay outdoors!
    I’m in southeast PA.

  2. These things have invaded my home! Not sure where they are getting in, but I probably remove 3 or 4 every day. Some are larger than others. They do no harm, but I wish they’d stay outdoors!
    I’m in southeast PA.


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