March Fly Bite: Is it Poisonous? Debunking the Myth

March flies, commonly found in wooded areas, are generally not known for their bites. Some species feed on nectar, pollen, and honeydew, while others don’t feed at all during their short lifespan. These insects play an important role as pollinators in orchards and for certain types of irises and orchids source.

While March flies aren’t known to have poisonous bites, one should be cautious when interacting with insects. For instance, allergic reactions to insect venom can cause swelling, itching, or even difficulty breathing if stung inside the mouth or throat source.

March Fly Bites: Overview and Fundamentals

Species of March Flies

March flies belong to the family Bibionidae and are typically found in wooded areas. Some of them have dark gray coloring, while others have bright spots of color. They are considered important pollinators for orchards, irises, and orchids1. Commonly encountered species include:

  • Deer flies
  • Black flies
  • Sand flies

Biting and Feeding Habits

March flies exhibit different feeding habits depending on the species. For example:

  • Deer flies feed on blood, primarily from livestock2.
  • Black flies bite mammals, including humans, to obtain blood3.
  • Sand flies have a similar feeding pattern, biting humans and animals for blood4.
Species Feeding Source Bite Effect
Deer flies Livestock Painful bites, can transmit diseases like tularemia5
Black flies Mammals Itchy, swollen bites; can transmit diseases like river blindness6
Sand flies Humans/Animals Painful, itchy bites; can transmit diseases like leishmaniasis7

However, not all March flies are known to be aggressive biters. The bites from some species, like deer flies and sand flies, can be quite painful, while bites from black flies tend to be itchy and swollen. It is important to note that March fly bites are not poisonous, but they can transmit diseases.

Are March Fly Bites Poisonous?

Venom and Chemicals Present

March flies are insects known for their painful bites. However, these bites are not generally considered poisonous. When a march fly bites, it releases saliva containing:

  • Anticoagulants
  • Enzymes

These chemicals help the fly during feeding but can cause itching and swelling for the person bitten.

Features of March Fly Bites:

  • Painful
  • Itching
  • Swelling

Transmitting Diseases

Although march fly bites are not directly poisonous, some species can transmit diseases, such as:

Diseases Symptoms Treatment
Tularemia Fever, skin ulcers, swollen glands, flu-like symptoms Antibiotics
Leishmaniasis Skin sores, ulcers, weight loss, fever, swollen spleen, and liver Antiparasitic drugs

Despite the possibility of transmitting diseases, march fly bites are generally more a source of temporary discomfort, rather than long-lasting or severe health concerns.

Symptoms and Allergic Reactions

Mild Reactions

March fly bites are usually not poisonous. However, they can cause mild allergic reactions in some people. Some common symptoms include:

  • Itching
  • Redness
  • Swelling

These symptoms usually subside after a short period of time.

Severe Reactions

In rare cases, people might experience more severe allergic reactions to March fly bites. These reactions might include:

  • Intense swelling
  • Severe itching
  • Painful welts

People with a history of severe allergic reactions to insect bites should be cautious and seek medical attention if they experience these symptoms.

Comparison Table: Mild vs Severe Reactions

Symptoms Mild Reactions Severe Reactions
Itching Yes Yes
Redness Yes No
Swelling Yes Intense
Painful Welts No Yes

It is important to differentiate between mild and severe reactions so that appropriate action can be taken if necessary. In case of severe reactions, medical assistance should be sought immediately.

Footnotes

  1. https://uwm.edu/field-station/march-fly/

  2. https://www.cdc.gov/ticks/avoid/on_people.html

  3. https://extension.unh.edu/resource/black-flies-fact-sheet

  4. https://www.cdc.gov/leishmaniasis/sand-flies/index.html

  5. https://www.cdc.gov/tularemia/transmission/index.html

  6. https://www.cdc.gov/riverblindness/index.html

  7. https://www.cdc.gov/leishmaniasis/index.html

Reader Emails

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 – March Flies

 

Subject: New to gardening
Location: Royal Palm Beach, Fl
March 15, 2014 8:42 am
Starting a new garden about two weeks ago. Just planted some seeds and starter plants. Noticed last night that these little bugs were everywhere. I think they might be fungus gnats. Some were mating. Climbing mostly on the wood of my raised garden bed. What are they and how do I get ride of them if they are bad bugs?
Signature: Cheri

March Fly
March Fly

Hi Cheri,
We are nearly certain that both of the images you submitted are of March Flies in the family Bibionidae, and we are certain they are of different sexes, and they might be of different species.  First we will discuss the male March Fly.  His big head and larger eyes are typical of the sexual dimorphism or visual difference between the sexes that is typical of this family.  He looks like he might be Bibio albipennis, based on images posted to BugGuide, and BugGuide indicates it is:  “The most common and widespread species of
Bibio.”  The female with her smaller head appears to be a different species because of the black wings.  She might be Dilophus orbatus, which is pictured on BugGuide.  The family page on BugGuide indicates:  “larvae live gregariously in the top layers of soil and leaf litter, rotten wood, and dung; adults often found on flowers” and “larvae feed on leaf and needle litter, decaying organic matter, also on subterranean structures of live plants.”  If you started your garden with rich compost, that might explain the large numbers of March Flies that are appearing in your garden.  BugGuide also notes:  “Adults emerge synchronously in huge numbers and often form dense mating aggregations. Males form loose “swarms” and copulate immediately with females as they emerge from the soil. After mating, female bibionines dig a small chamber in the soil with their fossorial fore tibiae, lay eggs, and die within the chamber (Plecia lay eggs on the soil surface). Adults are short-lived (3-7 days).”

Female March Fly
Female March Fly

 

Letter 2 – March Flies

 

Subject: what kind of insect is this?
Location: southeastern Pennsylvania
May 10, 2014 3:45 pm
I was playing with my son in the yard, when I felt something crawling on my leg. I let it walk onto my hand, and then I put it on the bush…didn’t want to squash them, while they were mating 🙂
We live in Southeast Pennsylvania, outside of Philadelphia. Photo was taken on May 09, 2014
Signature: Bob M.

March Flies
March Flies

Dear Bob,
These are March Flies in the family Bibionidae, and they are an example of extreme sexual dimorphism.  The male on the left has a large head and eyes, while the head and eyes on the female on the right are much smaller.  According to BugGuide:  “Adults emerge synchronously in huge numbers and often form dense mating aggregations. Males form loose “swarms” and copulate immediately with females as they emerge from the soil. After mating, female bibionines dig a small chamber in the soil with their fossorial fore tibiae, lay eggs, and die within the chamber (Plecia lay eggs on the soil surface). Adults are short-lived (3-7 days).”

Thank you for the quick reply. I appreciate the information, and your response.
Bob

Letter 3 – March Flies

 

Subject: Bug identification
Location: Long island new york
May 5, 2014 2:14 pm
What is this bug and how fo i get rid of it? Please help
Signature: Concerned home owner

March Flies
March Flies

Dear Concerned home owner,
These are March Flies and we believe we have correctly identified them as
Bibio fraternus thanks to images posted to BugGuide.  Many March Flies are sexually dimorphic, with males having bigger heads and huge eyes and females having much smaller heads and eyes.  We do not provide extermination advice.

Letter 4 – March Flies

 

Subject: Black, red-headed beetle.
Location: Coastal Connecticut, USA
October 2, 2016 12:29 pm
Please help me identify these little chaps. Our flowering plants are full of them. They seem to be browsing on the flowers, rather than eating the leaves (at least, so far).
Signature: Doug

March Flies
March Flies

Dear Doug,
These are not Beetles.  They are March Flies in the family Bibionidae, and we believe they may be female
Bibio longipes, a species according to BugGuide that is a  “fall-flying species. Females are distinguished by their reddish color.”

March Fly
March Fly

Letter 5 – March Flies from Iran

 

Subject: Bugs around almond trees
Location: 30KM South of Shiraz
April 16, 2013 9:50 am
Hello there,
I have a lot of these black insects around my almond trees in a garden near Shiraz, Iran.
I will be glad if you assist me identify these insects and if they are pest or not.
they look like peach tree borers but they are not.
They appear in early April every year and are present until mid May or end of May.
I can say almost 200 or 300 insects are flying or landing on each tree.
I can provide better images if needed, I will shoot using a professional camera next Friday and send the high quality images for you…
Kind Regards.
H. Razavieh
Signature: Hossein Razavieh

Male March Fly
Male March Fly

Dear Hossein,
These are March Flies in the family Bibionidae, and possibly in the genus
Bibio, and though we have not had any luck identifiying any Iranian species, you can see similar North American species on BugGuide as well as in our archive.  March Flies exhibit extreme sexual dimorphism, and the males have the larger heads with bigger eyes.  We are happy that you submitted a photo of each sex.  We would love to get better photos later in the month.  Please title the subject line March Flies from Iran.  We do not believe they are harming your almond trees.  According to BugGuide:  “larvae live gregariously in the top layers of soil and leaf litter, rotten wood, and dung; adults often found on flowers.”  BugGuide also notes:  “Adults emerge synchronously in huge numbers and often form dense mating aggregations. Males form loose “swarms” and copulate immediately with females as they emerge from the soil. After mating, female bibionines dig a small chamber in the soil with their fossorial fore tibiae, lay eggs, and die within the chamber (Plecia lay eggs on the soil surface). Adults are short-lived (3-7 days).”  BugGuide also states:  “larvae may damage cereal crops, vegetable crops, ornamental plants, nursery stock, grass, and forage crops; adult Bibio and Dilophus may be important pollinators in orchards and are the exclusive pollinators of some species of Orchidaceae and Iridaceae.”  Since they are short lived, they might not be around next week, but we would love to request a photo of a mating pair if possible.  One North American species found in Florida is known as the Love Bug because they are frequently found in flagrante delicto in large numbers.

Female March Fly
Female March Fly

 

Letter 6 – March Flies on Goldenrod

 

Small orange and black bug sucking on nectar of goldenrod
October 6, 2009
Hi. I came across this bug at my home in Sayville, New York. There were many individuals sucking the nectar from some goldenrod flower heads. I have never seen this bug before. What is this?
Derek Rogers
Sayville, New York

March Flies
March Flies

Hi Derek,
These are March Flies in the family Bibionidae.  We believe they are Dilophus spinipes, a species represented on BugGuide with several images taken  in New York a few days ago.  Those specimens were also pictured feeding on yellow flowers.  For some reason, we are unable to access any additional information on BugGuide this morning.  March Flies often appear in a very small window of time, and they appear in great numbers.  The infamous Love Bugs from the Southern States are a prime example.

March Fly

Authors

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  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com 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.

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