Black Horse Fly: All You Need to Know in a Quick Guide

folder_openDiptera, Insecta
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Black horse flies are a type of large, robust biting fly commonly found near bodies of water. These creatures are known for causing irritation and discomfort to both humans and animals alike. With their considerable size and pesky nature, it’s essential to understand how to identify and manage their presence effectively.

One key characteristic of black horse flies is their enormous compound eyes, often displaying colorful purple or green bands against a blue or yellowish-green background source. Additionally, they can vary in size, ranging from 0.25 to 1.25 inches long, and even come in different color variations depending on the species source.

Black horse flies breed in non-polluted water with high levels of dissolved oxygen, so their larvae and pupae can be found in various aquatic habitats such as large rivers, mountain streams, creeks, and waterfalls source. Understanding these key traits can help with the identification and control of black horse flies on your property, ensuring a reduction in their painful bites and annoyance.

Identification and Habitat

Color and Appearance

The Black Horse Fly (Tabanus atratus) is a large fly, typically measuring about 1 inch in length. Its key features include:

  • Body color: Black or dark brown
  • Eyes: Large and green or purple
  • Wings: Translucent with a dark tint

Range and Habitat

Black Horse Flies are commonly found in North America, particularly in the eastern and southern United States. Their preferred habitats include:

  • Ponds
  • Marshes
  • Damp woods

Distinguishing Black Horse Fly from Deer Flies and House Flies

Here’s a comparison table to help distinguish Black Horse Flies from Deer Flies, and House Flies:

Feature Black Horse Fly Deer Fly House Fly
Size ~1 inch ~1/4-1/2 inch ~1/8-1/4 inch
Color Black or dark brown Brownish-yellow with dark bands Gray with dark stripes
Eyes Large, green or purple Large, brightly colored Small, red or brownish
Wings Translucent, dark tint Translucent, dark bands Translucent, no tint

By noting differences in size, color, eyes, and wings, it becomes easier to identify a Black Horse Fly in comparison to Deer Flies and House Flies.

Life Cycle and Reproduction

Eggs and Larval Stages

Black horse flies begin their life cycle as eggs. Females typically lay clusters of 25-1,000 eggs on surfaces that are close to water, such as aquatic plants or wet soil.

  • Eggs are dark-colored and difficult to spot
  • Hatching occurs within 5-7 days

Upon hatching, the larvae emerge and immediately begin feeding on organic matter. They play an essential role in breaking down waste and other organic materials in the ecosystem.

  • Larvae are known as maggots
  • They undergo several molts to become larger

Livestock can be impacted by the larval stage, as black horse fly maggots can infest wounds or sores on animals, leading to potential infections.

Pupation and Adult Stage

Arthropoda, like black horse flies, undergo pupation and become adults. Larvae pupate in moist soil.

  • Pupation lasts 1-2 weeks
  • Adult black horse flies emerge from soil

Once they become adults, they focus on reproducing. Female horse flies require a blood meal to produce eggs, which may come from humans or wildlife.

  • Females are attracted to large mammals for their blood meal
  • Males feed on nectar and don’t bite animals or humans
Life Stage Time Frame Characteristics
Eggs 5-7 days Dark, near water
Larvae (maggots) Several months Feed on organic matter
Pupation 1-2 weeks Moist soil
Adult Varies Females require blood meal; Males feed on nectar

In conclusion, understanding the life cycle and reproduction of black horse flies is essential for their management and controlling their impact on livestock and humans.

Feeding and Impact on Humans and Animals

Biting Mechanism and Pain

Horse flies are known for their painful bites. They use their scissor-like mouthparts to cut through the skin and consume blood. The sensation of being bitten by a horse fly can be compared to a sharp pinch or a stab.

  • Painful bites due to scissor-like mouthparts
  • Comparable to a sharp pinch or stab

Female Horseflies and Blood Meals

Female horse flies primarily target mammals as their source of blood meals. They can detect their prey through the emission of carbon dioxide. Some common targets include humans, horses, and livestock. Male horse flies do not bite and instead feed on nectar.

  • Female horse flies need blood meals for reproduction
  • Mammals, including humans and livestock, are targeted
  • Male horse flies do not bite

Impact on Livestock and Horses

Horse flies can negatively impact livestock by causing discomfort, stress, and even disease transmission. One such disease is Equine Infectious Anemia (EIA), also known as swamp fever. This disease can cause severe anemia in horses and may have no cure.

Comparison Table: Mosquito vs. Horse Fly Bites

Mosquito Bite Horse Fly Bite
Not very painful Painful
Can carry diseases Can carry EIA
Slow fliers Fast fliers

In conclusion, horse fly bites are not only painful but can also lead to severe health consequences for humans and animals alike. Keeping animals in well-screened enclosures and using repellents can help minimize the risk of horse fly bites.

Prevention and Control

Insect Repellent and Fly Traps

Using insect repellent is a practical method to deter black horse flies from biting. They can be applied directly to the skin or clothing. For instance, DEET-based repellents are typically effective against tabanidae species.

Fly traps can also be a useful solution for controlling black horse flies in outdoor areas. Examples include the sticky fly trap and the homemade water traps.

Protective Clothing and Environmental Measures

Wearing light-colored clothing can help minimize the risk of black horse fly bites. Covering up exposed skin areas with loose and long-sleeved clothing is advisable when spending time outdoors in fly-prone areas.

Environmental measures can also be taken to reduce breeding sites, such as eliminating standing water and maintaining clean surroundings. Proper waste management and removal of decaying organic materials also contribute to limiting horse fly populations.

Managing Fly Populations on Livestock and Farms

For livestock owners, various strategies can be adopted to lessen the impact of black horse flies. Some measures include:

  • Applying fly repellents designed for animals, such as sprays or ointments
  • Installing fly traps around the farm to reduce the number of adult flies
  • Properly managing manure and waste to prevent breeding sites

Fly control on farms also involves maintaining clean surroundings, such as removing spilled feed, soiled bedding, and decaying grass clippings or hay.

Comparison Table: Insect Repellent vs. Fly Traps

Method Pros Cons
Insect Repellent Offers personal protection against horse fly bites May require reapplication, may not be effective against all fly species
Fly Traps Capture and reduce the number of adult flies in an area May not be sufficient in high-fly density areas, may require frequent cleaning and maintenance

Overall, a combination of insect repellent, fly traps, protective clothing, and environmental measures can effectively manage black horse fly populations and help you avoid painful bites. Remember always to monitor your surroundings and take precautions when outdoors during horse fly season.

Horse Fly Bites and Health Risks

Symptoms and Reactions

The black horse fly (Tabanus atratus) is a large, harmful insect belonging to the family Tabanidae and order Diptera. Found in humid areas like Florida, it is typically active during daylight hours in hot summer months. A black horse fly bite can cause various symptoms in humans and animals.

Some common reactions include:

  • Sharp pain, as their mandible and hooks tear the skin
  • Swelling
  • Redness
  • Itching

These reactions are due to the chemicals released by the fly to access the blood meal. In some cases, more severe symptoms may occur, such as:

  • Difficulty breathing
  • Dizziness
  • Allergic reactions

Infections and Diseases

Black horse flies can also transmit infections and diseases, particularly in horses. The most concerning infection is Equine Infectious Anemia (EIA), also known as swamp fever.

Symptoms in horses may include:

  • Fever
  • Weakness
  • Weight loss

Black horse flies can transmit EIA when they feed on an infected horse and subsequently on an uninfected one. The risk of infection is higher in areas with large horse fly populations, such as Canada and the wetlands of Florida.

Treatment and Remedies

After a black horse fly bite, it is essential to clean the wound to prevent bacterial infections. Over-the-counter treatments can help alleviate itching and swelling. Generally, affected individuals can use:

  • Ice packs or cold compresses for swelling
  • Antihistamines for itching and allergic reactions
  • Analgesics for pain relief

In conclusion, the black horse fly is a harmful insect that can cause painful bites, swelling, itching, and sometimes severe reactions. It can also transmit Equine Infectious Anemia in horses. Avoiding horse fly habitats, using insect repellents, and treating bites appropriately can help minimize the risk and impact of these unwanted pests.

Interesting Facts and Resources

The black horse fly belongs to the Tabanidae family, which consists of over 4,000 species, including deer flies and horse flies. These flies are known for their painful bites and transmit diseases among livestock animals.

Identification:

  • Large and robust size (0.25 to 1.25 inches long)
  • Huge compound eyes
  • Colorful bands on eyes
  • Abdomen and wing patterns vary by species

Here is a resource to help identify and learn more about horse and deer flies.

Facts:

  • Males prefer nectar, while females rely on blood meals for egg production
  • Active during daylight hours
  • Attracted to carbon dioxide and movement, making animals and humans targets

Horse and deer flies are found in a diverse range of aquatic habitats. These habitats include large rivers, mountain streams, creeks, and waterfalls.

Range:

  • Widespread across North America
  • Active from May to September in Wisconsin with over 30 species found in the region

Resources:

Feature Horse Fly Deer Fly
Size 0.5 to 1.25 inches long 0.25 to 0.5 inches long
Flight Straight and fast Erratic and slow

You can control flies by reducing breeding sites and using insecticides when necessary. Moreover, repellents can protect both humans and livestock from these pests.

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 – Black Horse Fly

 

black fly/bee thing
Hey,
This insect came in through an open door today in League City, Texas. It buzzed like a huge bee but looked more like a giant fly. It wouldn’t hold still very well for pictures but was pretty much all black….. body, wings, legs… pure black. It was approximately 1.5 inches long and had a huge mouth or nose area that appeared to expand in width and then be slim again = like a point you wouldn’t want to be poked with. Thanks for the help.
Leslie

Hi Leslie,
We are checking with Eric Eaton to see if he can identify the species of Black Horse Fly you photographed. It is in the genus Tabanus and females are blood suckers that bite painfully.

Update from Eric Eaton: (10/16/2005)
“Pretty sure this IS T. atratus. Don’t know of any other very large, all-black species. This one is a female (males have HUGE eyes that meet in the middle (top) of the head. This species is thought to be the Tlue-Tail Fly of folksong fame. Eric”

Letter 2 – Black Horse Fly

 

Black Horse Fly
Location:  Cumberland Plateau, rural southeast Tennessee
August 14, 2010 12:21 pm
Hello Daniel,
I thought I’d add to the growing collection of Black Horse Fly pictures. Seems that they are prolific this year! This one is a little over one inch long, and from earlier posts, I think is a female. If so, and the biting sex, I’m glad she was more interested in the top of my grill than in me.
Keep up the great work! It is amazing, entertaining, and informative.
Bob Kieffer

Black Horse Fly

Hi Bob,
As your email indicates, your specimen of a Black Horse Fly is a female as evidenced by the space between her eyes.  This is an excellent companion photo to the one we just posted a few hours ago of a male.

Letter 3 – Black Horse Fly

 

A fly?
This insect is very large. It was at least approx
1" long. Looks like a fly, buzzed like
a fly. Have never seen a fly (if this is what it
is) this large on our southwestern Wisconsin farm.
Thanks in advance.
Doug & Cindy Schriber

Hi Doug and Cindy,
This is a female Black Horse Fly, Tabanus atratus. The female,
which can be identified by the space between her eyes, is
the biting sex.

Letter 4 – Black Horse Fly

 

giant black fly
August 15, 2009
I found this huge fly in a wooded area by my work which is in Ajax, Ontario (just east of Toronto). It was well over an inch long, as you can see in the photo. I managed to take a picture, but the camera at my work was not the greatest, so the quality isn’t the best, but you can clearly see just how big this fly actually is.
any way is fine
Ajax, Ontario

Black Horse Fly
Black Horse Fly

Dear any way is fine,
This is a Black Horse Fly, Tabanus atratus.  Females of the species suck mammalian blood, but the males, like the one in your photo, are harmless.

Letter 5 – Black Horse Fly

 

Have not seen this before
Location:  Patchogue, NY on Long Island. Close to the Great South Bay.
August 13, 2010 6:17 pm
I live on Long Island in New York State.
I found this bug relaxing on the side of my home. I have never seen this type of bug before. It is a little more than long.
What is it?
Dean

Black Horse Fly

Hi Dean,
This behemoth of a fly is a Black Horse Fly,
Tabanus atratus.  Your photograph enables us to identify him as a male because of the close placement of the eyes.  The eyes of a female are spaced farther apart.  Only female Horse Flies bite.

Letter 6 – Black Horse Fly

 

Unidentified black fly in Herndon, VA.
Location: Herndon (4 miles from Dulles Airport), Virginia
August 12, 2011 4:55 pm
Hi Bugman,
We found this very cool all-black fly in the backyard yesterday just before dusk (8pm ish EST).
The body is all black, no color or shimmer anywhere not even in the wings or eyes. 2 large compound eyes – black. 2 wings are solid black in color and non-transparent. They attach at the shoulders either side of a flat black plate behind the head and close in a very wide v-shape.
Frontal abdomen shows distinct horizontal bands, black and hairless.
Dorsal abdomen is covered in black hair. Abdomen has rounded end but no ovipositor or other abdominal structure that I can see.
6 regualar fly legs, black, (did I mentions he is all black?)and two short splayed antennae at very top of head originating between eyes.
Last thing, couldn’t identify mouth parts but he has a very large depending proboscis – also black. He is more than 1in in length with wings longer. In the pics he (she?) is inside a drinking glass with an adult hand holding it for scale. Hope that helps. I hope you don’t have any questions because we released him after the photoshoot but we would truly love to know what kind of beastie he is. (I have more pics if you need them.) Many thanks in advance.
Signature: Anna & Aoife

Black Horse Fly

Hi Anna and Aoife,
Our editorial staff spent considerable time during our formative years in nearby Reston.  This is a Black Horse Fly,
Tabanus atratus, a species that depends upon an aquatic environment for the development of the larva, and the presence of livestock as a food source for the blood sucking female adults.  It is possible to tell the sexes apart by viewing the eyes, which alas, your photos do not provide the necessary details for that distinction.  The large eyes of the male are closer together, and they touch one another.  In the female, there is a space between the eyes.  See BugGuide for additional photos.

Mr Marlos – fabulous to get a reply from you, thank you.
Aoife is my 12yr old daughter who found and captured the fly.  She will be thrilled to receive your response.
So it’s a Black Horse Fly. It’s so big. I had no idea they could get that big.
As ex-Restonites you will know that there’s plenty of local aquatic environment to grow babies but not so much livestock any more. My dog regularly comes in with big bug bites on his hairless belly so perhaps we are doing our part for the species after all.
My apologies for the lack of eye-detail. It was coming on dusk and rather than hunt for the camera we took hasty shots with a cell phone. I cannot say for sure if the eyes were touching but we were happy to find the bug and even happier to know what it is. There are such marvellous creatures in your own back yard in this country. Long may they thrill us and thank you again for doing what you do.
Best regards from myself and my larvae.
Anna, Aoife, Jess & Sarah.

Letter 7 – Black Horse Fly

 

Subject: Large black insect – southern Ohio
Location: Southwest Ohio
July 3, 2014 2:04 am
I saw this large, all black insect flying outside our house early yesterday morning. It flew fairly slowly and landed near our garage. It seemed to have almost a “matte” finish . And it was about an inch long. Any idea what it is?
Signature: Adam

Black Horse Fly
Black Horse Fly

Hi Adam,
This is a Black Horse Fly,
Tabanus atratus, and the space between the eyes indicates she is a biting female.

Letter 8 – Black Horse Fly

 

black fly / moth / darth vader helmet
July 1, 2010
dear bugman, this bug is over an inch in length, and is entirely matte black, making me think it’s a night variety moth? but what drew my attention was it’s ‘darth vader helmet’ like listening devices (?) positioned like a globe over its head, and how it looked much like a bumble bee in flight. i was very surprised to see it was a moth body when it landed. have you seen this before? is it common here in MN? or is it a brazilian scout for a pending invasion? ha…thank you kindly for your efforts!
Uptown, Minneapolis, MN

Black Horse Fly

According to BugGuide, the Black Horse Fly, Tabanus atratus, is reported from Minnesota in July and August.

Letter 9 – Black Horse Fly: male on plants and female biting

 

Male Black Horsefly Sucking Blood?
Hello again,
It may please you to know that my 2 1/2-year-old son is finding both bugs (of which he went through a little terrified period just a couple weeks ago after a black ant pinched him kind of hard) and photography fascinating all of a sudden, since we’ve been spending a good bit of time browsing WTB looking for critters we’re turning up as spring springs here in our part of the world. With bugs he’s still not ready to touch them much, and when taking pictures he finds it easiest to aim the camera either straight down at something or to set it on a surface aimed at what he wants to capture, but it’s a good start on both fronts. Anyway, I was perusing pages looking for what I believe to be a rove beetle (but over an inch long), and we came across a post about a male black horse fly stating that only the females, which look noticeably different, suck blood. I thought critter in the attached pics was a black horse fly, but according to the description it must be a male so I’m wondering if anyone can explain the other attached pic? This was on my lower back, and of the six pics I took trying to get it’s mouthparts and the four other holes it punched in me (some of which you can just barely see around the little fella’s head) before it got this good one, only this image turned out at all clear. I let him eat as long as I could stand it, but I couldn’t wait for him to get his fill before I had to brush him away. This was also in Jacksonville, NC. Any thoughts? Peace,
Peace

Male Black Horse Fly Female Black Horse vFly


Hi again Peace,
You have correctly identified the male Blach Horse Fly, Tabanus atratus, on the plant, but if you look closely at the individual that is biting, you will see that there is a space between the eyes, indicating the she is a female. You must be quite limber to have gotten that photo of the feasting on your lower back. We expect to be seeing photos from your budding photographer in the future.

Ah! Thank you. I had fixated on this bit from an entry on The Big Black Horse Fly – “Females have smaller eyes *as well as having a white hairy thorax*” – rather than the entry on the Black Horse Fly. Thank you for clearing it up! We’ll definitely share anything DS captures that might be of use to WTB. I’m really looking forward to seeing what his eye is drawn to and how his personal photographic style develops. He sort of helped capture our possible rove beetle, but I can’t by any means credit him with having taken those pics, ‘though I will be sending one or two along for confirmation (if y’all have the chance to do so) once I get them uploaded, trimmed, and sized. As always, many thanks for your effort and dedication to this very good thing you’ve created. Take good care. :-> Peace,
Peace
PS I don’t know if I’m limber, or if the pain of the bite just distracted me from the pain of the stretch! 😀 I try to be generous with all the little critters in my immediate world so long as they’re not infesting homes or endangering lives, but dang, if these critters want to suck blood, they’ve gotta find a way to do it less painfully (and then maybe they can teach those skills to tax lawmakers.

Letter 10 – Black Horse Fly

 

Male Black Horse Fly, Tabanus atratus
Location: Columbia, Missouri
September 13, 2011 12:39 pm
Here’s a pic I thought you might like for your files. This marvelous beast of a fly was on a black truckbed liner, and very wary–got one shot. Found mid-June, mid-Missouri, at a small camp site in a rural area (farms around).
The color in this image was not edited in any way, FYI.
Thanks to your site, which I visit regularly (and link to, on my blog), I was able to positively identify it pretty easily. Thanks for all you do!
Signature: Lisa, aka ”Mycologista”

Black Horse Fly

Hi Lisa,
This is a positively gorgeous male Black Horse Fly and a gorgeous photograph as well.

Letter 11 – Black Horse Fly

 

Subject: big fly
Location: catoctin mountains, maryland
September 9, 2013 10:42 am
I saw this fly outside on the table and ran to snap a picture. Is it a horse fly? It is about an inch long and entirely black.
Signature: jenny

Black Horse Fly
Black Horse Fly

Dear Jenny,
Yes this is a Horse Fly, and as you noted, it is black, so it makes sense that it is commonly called a Black Horse Fly, Tabanus atratus.  Your individual is a blood sucking female Black Horse Fly as evidenced by the space between her eyes.  The males of the species, like all Horse Flies, have much larger, more close-set eyes.  One can only speculate that such sexual dimorphism is due to mating and sexual reproduction.  We guess that male Horse Flies use their large eyes with 360 degree vision to spot females.

Letter 12 – Black Horse Fly

 

Subject:  Black Horse Fly
Geographic location of the bug:  Quakertown, PA
Date: 07/09/2019
Time: 08:53 AM EDT
Your letter to the bugman:  In case you need another photo… these flies are big. After I saw it was a horse fly, I went back outside and killed it. (Horse farm 0.5mi up the street…)
How you want your letter signed:  JonKernPA

Black Horse Fly

Dear JonKernPA,
Thanks so much for submitting your image of a female Black Horse Fly.  Female Horse Flies can be identified because of the space between their eyes.  Male Horse Flies lack the space.  Female Horse Flies are the blood-suckers.  Males are harmless.

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 – Black Horse Fly

 

black fly/bee thing
Hey,
This insect came in through an open door today in League City, Texas. It buzzed like a huge bee but looked more like a giant fly. It wouldn’t hold still very well for pictures but was pretty much all black….. body, wings, legs… pure black. It was approximately 1.5 inches long and had a huge mouth or nose area that appeared to expand in width and then be slim again = like a point you wouldn’t want to be poked with. Thanks for the help.
Leslie

Hi Leslie,
We are checking with Eric Eaton to see if he can identify the species of Black Horse Fly you photographed. It is in the genus Tabanus and females are blood suckers that bite painfully.

Update from Eric Eaton: (10/16/2005)
“Pretty sure this IS T. atratus. Don’t know of any other very large, all-black species. This one is a female (males have HUGE eyes that meet in the middle (top) of the head. This species is thought to be the Tlue-Tail Fly of folksong fame. Eric”

Letter 2 – Black Horse Fly

 

Black Horse Fly
Location:  Cumberland Plateau, rural southeast Tennessee
August 14, 2010 12:21 pm
Hello Daniel,
I thought I’d add to the growing collection of Black Horse Fly pictures. Seems that they are prolific this year! This one is a little over one inch long, and from earlier posts, I think is a female. If so, and the biting sex, I’m glad she was more interested in the top of my grill than in me.
Keep up the great work! It is amazing, entertaining, and informative.
Bob Kieffer

Black Horse Fly

Hi Bob,
As your email indicates, your specimen of a Black Horse Fly is a female as evidenced by the space between her eyes.  This is an excellent companion photo to the one we just posted a few hours ago of a male.

Letter 3 – Black Horse Fly

 

A fly?
This insect is very large. It was at least approx
1" long. Looks like a fly, buzzed like
a fly. Have never seen a fly (if this is what it
is) this large on our southwestern Wisconsin farm.
Thanks in advance.
Doug & Cindy Schriber

Hi Doug and Cindy,
This is a female Black Horse Fly, Tabanus atratus. The female,
which can be identified by the space between her eyes, is
the biting sex.

Letter 4 – Black Horse Fly

 

giant black fly
August 15, 2009
I found this huge fly in a wooded area by my work which is in Ajax, Ontario (just east of Toronto). It was well over an inch long, as you can see in the photo. I managed to take a picture, but the camera at my work was not the greatest, so the quality isn’t the best, but you can clearly see just how big this fly actually is.
any way is fine
Ajax, Ontario

Black Horse Fly
Black Horse Fly

Dear any way is fine,
This is a Black Horse Fly, Tabanus atratus.  Females of the species suck mammalian blood, but the males, like the one in your photo, are harmless.

Letter 5 – Black Horse Fly

 

Have not seen this before
Location:  Patchogue, NY on Long Island. Close to the Great South Bay.
August 13, 2010 6:17 pm
I live on Long Island in New York State.
I found this bug relaxing on the side of my home. I have never seen this type of bug before. It is a little more than long.
What is it?
Dean

Black Horse Fly

Hi Dean,
This behemoth of a fly is a Black Horse Fly,
Tabanus atratus.  Your photograph enables us to identify him as a male because of the close placement of the eyes.  The eyes of a female are spaced farther apart.  Only female Horse Flies bite.

Letter 6 – Black Horse Fly

 

Unidentified black fly in Herndon, VA.
Location: Herndon (4 miles from Dulles Airport), Virginia
August 12, 2011 4:55 pm
Hi Bugman,
We found this very cool all-black fly in the backyard yesterday just before dusk (8pm ish EST).
The body is all black, no color or shimmer anywhere not even in the wings or eyes. 2 large compound eyes – black. 2 wings are solid black in color and non-transparent. They attach at the shoulders either side of a flat black plate behind the head and close in a very wide v-shape.
Frontal abdomen shows distinct horizontal bands, black and hairless.
Dorsal abdomen is covered in black hair. Abdomen has rounded end but no ovipositor or other abdominal structure that I can see.
6 regualar fly legs, black, (did I mentions he is all black?)and two short splayed antennae at very top of head originating between eyes.
Last thing, couldn’t identify mouth parts but he has a very large depending proboscis – also black. He is more than 1in in length with wings longer. In the pics he (she?) is inside a drinking glass with an adult hand holding it for scale. Hope that helps. I hope you don’t have any questions because we released him after the photoshoot but we would truly love to know what kind of beastie he is. (I have more pics if you need them.) Many thanks in advance.
Signature: Anna & Aoife

Black Horse Fly

Hi Anna and Aoife,
Our editorial staff spent considerable time during our formative years in nearby Reston.  This is a Black Horse Fly,
Tabanus atratus, a species that depends upon an aquatic environment for the development of the larva, and the presence of livestock as a food source for the blood sucking female adults.  It is possible to tell the sexes apart by viewing the eyes, which alas, your photos do not provide the necessary details for that distinction.  The large eyes of the male are closer together, and they touch one another.  In the female, there is a space between the eyes.  See BugGuide for additional photos.

Mr Marlos – fabulous to get a reply from you, thank you.
Aoife is my 12yr old daughter who found and captured the fly.  She will be thrilled to receive your response.
So it’s a Black Horse Fly. It’s so big. I had no idea they could get that big.
As ex-Restonites you will know that there’s plenty of local aquatic environment to grow babies but not so much livestock any more. My dog regularly comes in with big bug bites on his hairless belly so perhaps we are doing our part for the species after all.
My apologies for the lack of eye-detail. It was coming on dusk and rather than hunt for the camera we took hasty shots with a cell phone. I cannot say for sure if the eyes were touching but we were happy to find the bug and even happier to know what it is. There are such marvellous creatures in your own back yard in this country. Long may they thrill us and thank you again for doing what you do.
Best regards from myself and my larvae.
Anna, Aoife, Jess & Sarah.

Letter 7 – Black Horse Fly

 

Subject: Large black insect – southern Ohio
Location: Southwest Ohio
July 3, 2014 2:04 am
I saw this large, all black insect flying outside our house early yesterday morning. It flew fairly slowly and landed near our garage. It seemed to have almost a “matte” finish . And it was about an inch long. Any idea what it is?
Signature: Adam

Black Horse Fly
Black Horse Fly

Hi Adam,
This is a Black Horse Fly,
Tabanus atratus, and the space between the eyes indicates she is a biting female.

Letter 8 – Black Horse Fly

 

black fly / moth / darth vader helmet
July 1, 2010
dear bugman, this bug is over an inch in length, and is entirely matte black, making me think it’s a night variety moth? but what drew my attention was it’s ‘darth vader helmet’ like listening devices (?) positioned like a globe over its head, and how it looked much like a bumble bee in flight. i was very surprised to see it was a moth body when it landed. have you seen this before? is it common here in MN? or is it a brazilian scout for a pending invasion? ha…thank you kindly for your efforts!
Uptown, Minneapolis, MN

Black Horse Fly

According to BugGuide, the Black Horse Fly, Tabanus atratus, is reported from Minnesota in July and August.

Letter 9 – Black Horse Fly: male on plants and female biting

 

Male Black Horsefly Sucking Blood?
Hello again,
It may please you to know that my 2 1/2-year-old son is finding both bugs (of which he went through a little terrified period just a couple weeks ago after a black ant pinched him kind of hard) and photography fascinating all of a sudden, since we’ve been spending a good bit of time browsing WTB looking for critters we’re turning up as spring springs here in our part of the world. With bugs he’s still not ready to touch them much, and when taking pictures he finds it easiest to aim the camera either straight down at something or to set it on a surface aimed at what he wants to capture, but it’s a good start on both fronts. Anyway, I was perusing pages looking for what I believe to be a rove beetle (but over an inch long), and we came across a post about a male black horse fly stating that only the females, which look noticeably different, suck blood. I thought critter in the attached pics was a black horse fly, but according to the description it must be a male so I’m wondering if anyone can explain the other attached pic? This was on my lower back, and of the six pics I took trying to get it’s mouthparts and the four other holes it punched in me (some of which you can just barely see around the little fella’s head) before it got this good one, only this image turned out at all clear. I let him eat as long as I could stand it, but I couldn’t wait for him to get his fill before I had to brush him away. This was also in Jacksonville, NC. Any thoughts? Peace,
Peace

Male Black Horse Fly Female Black Horse vFly


Hi again Peace,
You have correctly identified the male Blach Horse Fly, Tabanus atratus, on the plant, but if you look closely at the individual that is biting, you will see that there is a space between the eyes, indicating the she is a female. You must be quite limber to have gotten that photo of the feasting on your lower back. We expect to be seeing photos from your budding photographer in the future.

Ah! Thank you. I had fixated on this bit from an entry on The Big Black Horse Fly – “Females have smaller eyes *as well as having a white hairy thorax*” – rather than the entry on the Black Horse Fly. Thank you for clearing it up! We’ll definitely share anything DS captures that might be of use to WTB. I’m really looking forward to seeing what his eye is drawn to and how his personal photographic style develops. He sort of helped capture our possible rove beetle, but I can’t by any means credit him with having taken those pics, ‘though I will be sending one or two along for confirmation (if y’all have the chance to do so) once I get them uploaded, trimmed, and sized. As always, many thanks for your effort and dedication to this very good thing you’ve created. Take good care. :-> Peace,
Peace
PS I don’t know if I’m limber, or if the pain of the bite just distracted me from the pain of the stretch! 😀 I try to be generous with all the little critters in my immediate world so long as they’re not infesting homes or endangering lives, but dang, if these critters want to suck blood, they’ve gotta find a way to do it less painfully (and then maybe they can teach those skills to tax lawmakers.

Letter 10 – Black Horse Fly

 

Male Black Horse Fly, Tabanus atratus
Location: Columbia, Missouri
September 13, 2011 12:39 pm
Here’s a pic I thought you might like for your files. This marvelous beast of a fly was on a black truckbed liner, and very wary–got one shot. Found mid-June, mid-Missouri, at a small camp site in a rural area (farms around).
The color in this image was not edited in any way, FYI.
Thanks to your site, which I visit regularly (and link to, on my blog), I was able to positively identify it pretty easily. Thanks for all you do!
Signature: Lisa, aka ”Mycologista”

Black Horse Fly

Hi Lisa,
This is a positively gorgeous male Black Horse Fly and a gorgeous photograph as well.

Letter 11 – Black Horse Fly

 

Subject: big fly
Location: catoctin mountains, maryland
September 9, 2013 10:42 am
I saw this fly outside on the table and ran to snap a picture. Is it a horse fly? It is about an inch long and entirely black.
Signature: jenny

Black Horse Fly
Black Horse Fly

Dear Jenny,
Yes this is a Horse Fly, and as you noted, it is black, so it makes sense that it is commonly called a Black Horse Fly, Tabanus atratus.  Your individual is a blood sucking female Black Horse Fly as evidenced by the space between her eyes.  The males of the species, like all Horse Flies, have much larger, more close-set eyes.  One can only speculate that such sexual dimorphism is due to mating and sexual reproduction.  We guess that male Horse Flies use their large eyes with 360 degree vision to spot females.

Letter 12 – Black Horse Fly

 

Subject:  Black Horse Fly
Geographic location of the bug:  Quakertown, PA
Date: 07/09/2019
Time: 08:53 AM EDT
Your letter to the bugman:  In case you need another photo… these flies are big. After I saw it was a horse fly, I went back outside and killed it. (Horse farm 0.5mi up the street…)
How you want your letter signed:  JonKernPA

Black Horse Fly

Dear JonKernPA,
Thanks so much for submitting your image of a female Black Horse Fly.  Female Horse Flies can be identified because of the space between their eyes.  Male Horse Flies lack the space.  Female Horse Flies are the blood-suckers.  Males are harmless.

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.

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.

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.

Authors

  • 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.

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  • 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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Tags: Horse Fly

Related Posts

66 Comments. Leave new

  • Celina Michaeli
    July 23, 2013 5:44 pm

    I found one in Chatham Ontario. Canada is that normal?? I’ve never seen one before?

    Reply
  • I found one of those huge black flies on my third floor balcony this morning here in Peterborough, Ontario. Why is it that most of us have never seen these giants?

    Reply
  • I saw one today in Greely, Ontario. It was so large I thought it was a moth.. Lol
    glad the males don’t bite at least 🙂

    Reply
  • I saw one today in Greely, Ontario. It was so large I thought it was a moth.. Lol
    glad the males don’t bite at least 🙂

    Reply
  • Thank you so much, bug experts! I found one of the guys during my shift at the local park. We have plenty of water, but no livestock like the poster.

    Reply
  • I found your black horse fly here of u can contact me back …

    Reply
  • I just killed one of those today in South Dakota. It landed on my horses and was biting her. I smashed it with my cell phone. Dirty buggers.

    Reply
  • Spotted one large, definitely female, on my front porch here in Bossier, Louisiana. Ours is the only watered lawn so with the temps I wasn’t shocked to see a horsefly, or one of thst size, as we’ve had an unusually large amount this year. The difference was the striking solid black and it seemed bigger than the usual 1-1/2″ , so maybe it was 2″, but I threw everything out of my hands to get inside because I know even small regular horseflies HURT and I swear it appeared like came from hell itself. Gladly I can sleep knowing now that they’re somewhat recognized and not biblical.

    Reply
  • In new orleans just had one in my car. They are massive

    Reply
  • Susan Parks
    July 20, 2016 4:42 pm

    This looks EXACTLY like the ones that hang out around my front porch this time of year…lots of bright sun and my porch rails are painted deep dark black. These flies are enormous and zoom in like stelth bombers but do well to avoid me and sit still for extended periods. Saw one today at least 1-1/2″x1/2″ and at close observation appeared to be covered in fur. Though I live in the country where there may be horses or cattle, I only have seen flies like this on my porch.

    Reply
  • One of these giants landed on the back of my horse today. It looked like a black hummingbird at first, because there was no way that was a regular horse fly. When I looked more closely, it looked like a fly on steroids, except jet black with translucent black wings.

    Reply
  • BARBARA ZEBROSKI
    August 10, 2016 7:19 am

    We have them here on Long Island .I call them black back bugs(For lack of a better description) . LOL They land on the horses back and I have seen the stingers come out and dig into their spines or butt causing the horses to buck and run to try to get away. The bugs will follow them. They are horrible.

    Reply
  • We have been seeing them only lately here in the northern New Jersey area, mostly in our woods. And yes they do follow/ chase us ! One landed on our dog and she kept trying to eat it. Ugh. Monstrous.

    Reply
  • I lived on Long Island all my life, never saw them. I moved to SC 5 years ago, and the bugs are huge ! Saw this black fly 3 times in the last 2 days. No horses around, and they chase you.

    Reply
  • Live in NE Iowa just N of Decorah.
    My dog was outside working at killing a small mouse,(I thought), but it was this huge black fly! It resembled a horse fly. I had a plastic bag in my hand and when I saw it was not a mouse but a fly I had never seen before, I picked it up with the bag and put it in a jar. It was missing a leg and one wing was askew, but very alive.
    I am 63, lived in this area all my life and have never seen this bug!

    Reply
  • Live in NE Iowa just N of Decorah.
    My dog was outside working at killing a small mouse,(I thought), but it was this huge black fly! It resembled a horse fly. I had a plastic bag in my hand and when I saw it was not a mouse but a fly I had never seen before, I picked it up with the bag and put it in a jar. It was missing a leg and one wing was askew, but very alive.
    I am 63, lived in this area all my life and have never seen this bug!

    Reply
  • Paula Robinson
    May 25, 2017 8:51 pm

    We had one of these HUGE flies by the front door tonight! All black approx. 1.5 inches long. Big mouth, ugh!

    Reply
  • Jena Linehan
    July 30, 2017 11:27 am

    Northern NY, 1000 islands area. Found on back deck. Same size and color as described in other posts. We have fly shooters, (sorry bug lovers) and my husband is a pro with them!! This is one fly that won’t be bothering the baby calves next door any longer!!

    Reply
  • Sue Beaulieu
    August 5, 2017 7:01 am

    We also just had a very large black fly on our truck liner. We had to look it up and found out what he is on your website. We are in New Hampshire.

    Reply
  • I just took a picture and a video of one of these flies. I didn’t know what it was. I had to look up big black flying bugs. It is beautiful.

    Reply
  • Jeffery Williams
    August 26, 2017 11:00 am

    One flew into my SUV in central Illinois, freaked me out.

    Reply
  • We just saw one of these in the yard by the pool. My son won’t go back out to clean up now. We are in the northern Ca. Are they afraid of anything or what can I kill it with from afar?

    Reply
  • Jason Miners
    June 15, 2018 4:17 pm

    We live in London Ontario Canada. Just saw a massive black fly. Looked like a house fly but the size of a small cockroach. The one pictured above was definitely the same kind. A 40 year old country kid, this is the first time I’ve ever seen one. Thank you for the information.

    Reply
  • Sara Lewis Meyer
    June 23, 2018 4:53 pm

    Just saw one on deck flower box in Paducah, KY. I appreciate the ID tips and photos.

    Reply
  • I have an all black horse and moved him to a new boarding facility this past Fall. This spring, I have been seeing these ENORMOUS flies. While other flies, horseflies, etc. bounce off my freshly fly sprayed boy, these atrocities just land on his back and torment him. They’re QUICK too! It’s easy to swat horseflies with my hand but these are too quick!
    I use a homade fly spray with Skin So Soft, apple cider vinegar, water and essential oils. I may try regular commercial sprays to see if they work. Anyone else have something that works?

    Reply
  • I have an all black horse and moved him to a new boarding facility this past Fall. This spring, I have been seeing these ENORMOUS flies. While other flies, horseflies, etc. bounce off my freshly fly sprayed boy, these atrocities just land on his back and torment him. They’re QUICK too! It’s easy to swat horseflies with my hand but these are too quick!
    I use a homade fly spray with Skin So Soft, apple cider vinegar, water and essential oils. I may try regular commercial sprays to see if they work. Anyone else have something that works?

    Reply
  • Kings Queen.
    July 11, 2018 11:07 am

    Just had one on the back passenger window when I went to put my baby in his carseat. I freaked out bc I had no idea what it was. We ended up jumping n through the driver side nd that sucker stayed there till we got to the corner.

    Reply
  • I live in the middle of Maryland and saw one of these today on my car. I had never seen one so large, but we have had the worst year in along time for horse flies. It’s the first year I’ve considered getting a fly blanket for my horse. Now I feel like I want to wrap all our horses from head to toe in some protection with that monster flying around. Guess I need to go get a case of liquid Benadryl for the barn along with a gallon of lidocaine for the pain. On horses and cows the welt can be anywhere from 2 to 4 inches in diameter and stays sore for weeks.

    Reply
  • We just found one of these on our pool deck in Eastern Massachusetts. How bad is the bite from one of them?

    Reply
  • just found one in aurora il i got it in a powerade bottle if i had known it was dangerous i wouldve left it alone lol

    Reply
  • Charlene Szarek
    August 10, 2018 4:17 pm

    I just saw one of these today in Southern New Hampshire.

    Reply
  • Charlene Szarek
    August 10, 2018 4:19 pm

    I just saw one of these today in Southern New Hampshire!

    Reply
  • Hi, I’m from Baltimore, Maryland. I saw a huge all black horse fly in my backyard today! I live in the city and I have an urban garden. My vegetables are all growning in containers. There are no farm animals in my area. I was able to get a picture.

    Reply
  • Joanette Daniels
    August 25, 2018 12:11 am

    I just chased one out of my house. Opened the door to let my car in and he was trying to catch it. Thought it was a big moth at first until I got a good look at it. Biggest damn fly I have ever seen. I love North of Boise Idaho.

    Reply
  • Sharlene Hempel
    September 30, 2018 5:46 pm

    Just saw one of these large black flies for the first time on my property of 40 years. It was lethargic and clinging to a twig as I moved it around. I am in South East Texas. I thought it was just bigger because it was Texas 🙂 . Your comments have been helpful.

    Reply
  • Randi Victor
    May 22, 2019 4:57 am

    We have one in our house right now. My husband tried to get rid of it last night and he wound up putting a hole in our wall and gave up.

    We live in a rural area of Florida and all our neighbors have livestock. We don’t even have a dog, but our 3 kids are wild enough to be considered animals.

    We had an incident last night where the fire rescue had to come and they left our door open, which is where we think this beast of a fly came in. It is solid black and I thought it was a large moth at first. Then when my husband saw it, he said that it was a black horse fly. So of course I looked it up and scared myself to bits. I immediately took off my dark blue dress because it is attracted to large dark objects.

    Well, woke up this morning to get the kids ready for school, and wouldnt you know, that darn fly is sitting on the wall next to the light. Today is the day!

    Reply
  • Randi Victor
    May 22, 2019 4:57 am

    We have one in our house right now. My husband tried to get rid of it last night and he wound up putting a hole in our wall and gave up.

    We live in a rural area of Florida and all our neighbors have livestock. We don’t even have a dog, but our 3 kids are wild enough to be considered animals.

    We had an incident last night where the fire rescue had to come and they left our door open, which is where we think this beast of a fly came in. It is solid black and I thought it was a large moth at first. Then when my husband saw it, he said that it was a black horse fly. So of course I looked it up and scared myself to bits. I immediately took off my dark blue dress because it is attracted to large dark objects.

    Well, woke up this morning to get the kids ready for school, and wouldnt you know, that darn fly is sitting on the wall next to the light. Today is the day!

    Reply
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  • Just saw one of these in Big Prairie Ohio. I did not like the looks of it. A lot of farms around here. Thanks for the info.

    Reply
  • Found two giant ones in my pool! I live in Waterford Michigan !!

    Reply
  • Glengarry ON, just saw one last week with my husband on our back porch. We have never seen anything close to the size of this. Very scary! To think these could sting too? Unimaginable!

    Reply
  • JUST SAW ONE–NO HORSES WITHIN TWO MILES.I HAVE NEVER SEEN THE LIKES OF IT BEFORE. YORKTOWN HEIGHTS NEW YORK

    Reply
  • Everyone is posting that they either have seen or that they have the bugs around their home. However no one has said what the bug is or if it can bite/sting you. If someone knows please let everyone know what it is or may be please. Thank You,
    Brian W.

    Reply
  • Everyone is posting that they either have seen or that they have the bugs around their home. However no one has said what the bug is or if it can bite/sting you. If someone knows please let everyone know what it is or may be please. Thank You,
    Brian W.

    Reply
  • are these flies harmful to plants or animals?

    Reply
    • Female Horse Flies bite and suck blood from larger mammals, but plants are perfectly safe around them.

      Reply
  • Growing up poor, in the South in the 50’s, we spent much of our summertime outside entertaining ourselves doing the usual kid stuff. We would catch the big Black Horsefly, tie a length of thread around its neck, holding on to one end, we’d let them go and fly them around. It was fun!

    Reply
  • Aneleh Southey
    February 1, 2020 12:17 pm

    Hi I live in Cape Town South Africa out in a town called Wellington and we found this fly on our horses today. Never new the live here and they carry virus and bacteria

    Reply
  • Zara Pendley
    July 29, 2021 4:20 pm

    One of these flew into my house late last night
    here in St Augustine, FL.

    Reply
  • Just found one here in Davie, FL. Female. There are horse stables nearby.

    Reply
  • I have them in my backyard in Delaware. Why have I never seen this book before? I’m 54 years old. LOL.

    Reply
    • Yes we have them now too, they have never been around here before. Green heads and sheep fies are bad enough but now these too whats going on..

      Reply
  • Just had one get inside my mothers house. And I’m in Florida.

    Reply
  • Hi there, I hope someone reads this in 2021! 🙂 I was hoping someone might know about any diseases this fly might be able to transfer to hu.ans….?… I’m personally dealing with a situation concerning possible parasitic infection; and I’ve been seeing this “fly” hanging out for the last 3 days. It’s not dead, I know for sure cause when I took It’s picture, it stirred it up a bit….Anyway, thought I’d give my hopes and luck a shot here at your site and forum. 🙂 Thank You Truly,
    L Crystal R

    Reply
  • Ps from L Crystal R…I cannot seem to figure out how to post a picture of the creature ! I’m still trying ~

    Reply
  • Got bitten in Jacksonville, Florida. The bug is the same color as matte black bumper on vehicle as I just saw again Today after I got chomped twice three days ago.
    The wounds swelled, still itch & with blood scars formed.

    Reply
  • Richmond,VA Just saw one for the first time in my 70 years. It must have been at least 1 1/2 inches. Sat on the window frame for about 10 minutes then moved on.

    Reply

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