Marsh Fly: All You Need to Know for a Buzz-Free Outing

folder_openDiptera, Insecta
commentNo Comments

Marsh flies belong to the family Bibionidae and are often found in wetland environments. These small insects are important pollinators and decomposers within their ecosystems. One common species found in North America is Bibio slossonae, which can be observed during their cold-weather flights in late fall [1].

These tiny creatures are fascinating to study, not only for their ecological roles but also for their unique life cycles. For instance, adult marsh flies have a relatively short lifespan, while larvae live for a longer period, contributing to decomposition and nutrient cycling in their habitats. As the climate changes, marsh fly populations may experience shifts in their distribution and abundance, making them useful indicators of environmental health.

Understanding Marsh Flies

Taxonomy and Family

Marsh flies belong to the family Sciomyzidae and are commonly found in damp areas. They are not to be confused with March flies which are part of the Bibionidae family.

Physical Characteristics

Marsh flies display some distinct physical traits:

  • Antennae: These insects possess long, segmented antennae.
  • Eyes: Males typically have larger eyes compared to females.

Here’s a comparison of Marsh flies with March flies:

Feature Marsh Fly March Fly
Family Sciomyzidae Bibionidae
Habitat Damp areas Diverse habitats
Eye size Males have larger eyes Female eyes often smaller

Marsh flies are an interesting insect that can be distinguished by their unique physical features and their classification within the taxonomic family Sciomyzidae.

Life Cycle and Habitat

Breeding and Eggs

Adult marsh flies mate during their short lifespan of a few weeks. They lay eggs in damp soil near freshwater marshes, lakes, and ponds. Some examples of their preferred breeding habitats include:

  • Wetlands
  • Aquatic plants close to the water surface
  • Decaying vegetation

Larvae and Pupation

After hatching, the larvae feed on a variety of organic matter, including decaying plants, as well as aquatic insects and terrestrial snails. These carnivorous habits make them natural predators of mosquitoes and, consequently, control the spread of diseases like schistosomiasis.

Marsh fly larvae have several features that help them navigate their environment:

  • Elongated, worm-like bodies
  • Head concealed within the thorax
  • Fleshy protuberances called prolegs

Once the larvae have completed their development, they pupate above ground or within moist soil. They emerge as adult marsh flies, ready to reproduce and continue their life cycle.

Feature Marsh Fly Larva Terrestrial Snail
Habitat Freshwater marshes, lakes, and ponds Terrestrial ecosystems, such as gardens, forests, and grasslands
Food Source Decaying plants, aquatic insects, and snails Algae, fungi, and plant materials
Role in Ecosystem Mosquito control, breakdown of organic matter Decomposers, nutrient recycling, and food source for other organisms

Pros of Marsh Flies:

  • Biological control of mosquitoes
  • Helps in breaking down organic matter in aquatic ecosystems

Cons of Marsh Flies:

  • May be a nuisance in large numbers
  • Can sometimes cause discomfort or mild allergic reactions in humans

Feeding and Predation

Prey and Hunting Strategies

The marsh fly, also known as the snail-killing fly, is predominantly found in wooded areas and often feeds on nectar, pollen, and honeydew, depending on the species (source). Some marsh fly adults don’t feed at all. Interestingly, these insects are important pollinators, particularly for:

  • Orchards
  • Irises
  • Orchids

Their larvae are quite different, feeding on various organic matter and sometimes preying on creatures like snails. These primitive-looking larvae aggregate in masses when feeding.

Marsh Fly Predators

Marsh flies have their share of predators, too. Birds are typical predators that find nourishment from marsh flies in their natural habitats. Other insects, such as larger predatory insects and spiders, also prey on these flies.

In summary, marsh flies play a role in pollination and the woodland ecosystem’s balance. They feed on nectar, pollen, and honeydew, while their larvae enjoy organic matter and occasionally hunt snails. Predators like birds and other insects help keep the marsh fly population under control.

Importance and Contributions to Ecosystem

Pest Control

The Marsh Fly (Family Bibionidae) plays a significant role in pest control. Their larvae feed on decaying organic matter, helping to break down and recycle nutrients in the ecosystem. This assists in maintaining healthy soil conditions for various plant species. In addition, Marsh Flies are important pollinators for certain plants such as orchids and irises, improving plant reproduction and growth.

Arthropod Biodiversity

Marsh Flies are a key element of arthropod biodiversity. They belong to the order Diptera, the same order as mosquitoes and houseflies. Arthropod diversity is crucial for maintaining ecosystem balance and stability. Marsh Flies and other arthropods provide food for predators, contribute to nutrient cycling, and support overall ecosystem health.

The Marsh Fly is an important contributor to ecosystems primarily through its roles in pest control and arthropod biodiversity. These roles emphasize their significance in maintaining a balanced and healthy environment.

Some features of Marsh Flies include:

  • Adults feed on nectar, pollen, and honeydew
  • Some adult species do not feed at all
  • Larvae feed on decaying organic matter
  • Important pollinators for certain plants
  • Contribute to arthropod biodiversity

Marsh Fly Identification and Observation

Clickable Guide and Resources

One way to identify and observe marsh flies is through a clickable guide, which typically features lists of species, images, and additional resources. By using such guides, you can conveniently compare and contrast different marsh fly species.

  • Clickable guides provide:
    • Images for visual comparison
    • Descriptions of distinguishing features
    • Links to further resources

Expert Professional Advice

Seeking skilled advice from experts, such as your local extension office, is another effective method for marsh fly identification.

  • Expert advice can offer:
    • Insights into specific habitats
    • Tips for successful observation
    • Guidance on contributing to citizen science projects

Remember to exploit available resources, such as guidebooks, online resources, and local expertise, to make the most of your marsh fly observation experience.

Marsh Fly Distribution and Conservation

Marsh Flies Across the United States

Marsh flies, belonging to the Bibionidae family, can be found in various locations across the United States.

Threats and Conservation Efforts

Marsh flies inhabit wetland areas, which are sensitive ecosystems. The threats to wetlands in the United States include:

  • Habitat loss
  • Invasive species
  • Climate change

Habitat loss can happen due to urbanization, agriculture, and industrial practices, making it one of the major concerns for marsh fly conservation.

On the other hand, invasive species pose threats to marsh fly populations by competing for resources like food and shelter.

Climate change can affect marsh fly populations indirectly by shifting their habitats, causing changes in vegetation, and altering the water levels in wetlands.

To combat these issues, various conservation efforts are being undertaken, such as the restoration of high marsh habitats in large areas like the Great Marsh. Other initiatives like the Habitat Conservation Plan Handbook guide the conservation and management of sensitive species, including marsh flies.

The Nationwide Marsh Vulnerability Maps provide information about the most vulnerable marshes across the United States, helping to target conservation efforts more effectively.

The Distribution Mapping and Analysis Portal (DisMAP) allows users to track and understand species distributions, including those of marsh flies, to inform conservation and restoration decisions.

By protecting and preserving wetland habitats, we can ensure that marsh flies and other interconnected species thrive in the United States.

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 – Marsh Fly


Subject:  Friendly fly from Manitoba
Location:  Pacey Lake, Manitoba, Canada
June 12, 2016
Hi Daniel.  I haven’t posted on this site for a while, so I thought I might share this one that I photographed a few days ago. The ‘smiley face’ image is a surprisingly common theme in insect decoration; especially if you have an active imagination. This, however, is by far the most perfect and obvious that I have ever seen. It’s a Marsh Fly (Sciomyzidae: Tetanocera plebeja), sometimes called snail-killing flies because their larvae are parasitoids of snails. Cheers. Karl

Marsh Fly
Marsh Fly

Hi Karl,
We were away from the office when you sent your wonderful image.  There was no Marsh Fly category on the site, so a new category was created to accommodate your awesome image of a smiley faced Marsh Fly.  According to BugGuide:  “‘Noting the pattern on the wings is the quickest means of determining this common and widespread species.’ — Bill Murphy”

Letter 2 – Marsh Fly


Subject: Is this a fly?
Location: Mechanicsburg, PA
July 15, 2017 8:22 pm
Hi Bugman!
This guy was hanging out on our deck railing this afternoon. It’s a new one for me and I’d love to know what it is. I’m pretty good about looking things up, but I’m stumped and need the experts. It has fly looking eyes, but those wings are unique. It wouldn’t be a peacock fly with its wings down, would it? (One of those stopped by a couple years ago. First and only sighting.) It was the size of a lightning bug.
Signature: Perplexed in PA

Marsh Fly

Dear Perplexed in PA,
We believe this unique looking fly is a Marsh Fly,
Euthycera arcuata, thanks to this BugGuide image.  According to BugGuide:  “‘Very distinctive species with a unique closed-wing shape.’ –Bill Murphy.”  Of the family, BugGuide notes:  “adults around marshes, lakes, ponds, or wooded areas; larvae are aquatic” and “larvae parasitize or prey on freshwater or terrestrial snails.”

Thank you so much! That definitely looks like a match! We do have boggy/marshy areas near our house and I’ve seen snails in certain areas of our yard. That’s so interesting. Some bugs are familiar and easy to spot – seasonal regulars. Others are chance encounters never to be seen again. I love discovering what’s right in my own backyard!


  • 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.

    View all posts
  • 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.

    View all posts
Tags: Marsh Fly

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *

Fill out this field
Fill out this field
Please enter a valid email address.
You need to agree with the terms to proceed