Black Fly vs Horse Fly: Uncovering the Key Differences and Impacts

folder_openDiptera, Insecta
comment1 Comment

Black flies and horse flies are both bothersome insects that can disrupt outdoor activities and even cause painful bites. These two types of flies have different characteristics and habitats, which can help us understand their behavior and find ways to prevent or manage their presence.

Black flies typically develop in flowing water, often found in environments such as rivers, mountain streams, creeks, and waterfalls source. They are smaller in size and can be found in various habitats. On the other hand, horse flies are larger and usually develop in marshes, ponds, and streams source. In some cases, they can also be found in saltwater marshes. Their coloration can range from all black to having colored patterns on their abdomens and wings source.

When dealing with these pests, it’s essential to know their distinguishing features and habitats, as this will aid in implementing effective control measures. For instance, horse fly traps can be a helpful tool for managing their population in specific environments. Rest assured, by understanding these flies better, we can reduce their impact on our outdoor experiences and maintain our surroundings.

Overview and Description of Black Flies and Horse Flies

Visual Differences

Black flies and horse flies are two distinct species of flies. Black flies are smaller, ranging from 5 to 15 mm in size, with a robust appearance and an arched thoracic region. They typically have a black body, large compound eyes, short antennae, and a pair of large, fan-shaped wings – although, yellow and orange species also exist.

On the other hand, horse flies are larger. In Texas, there are over 100 species of horse and deer flies, with deer flies ranging from 1/4 to 1/2 inch long. They have black to brown coloration, often with yellowish markings, and their live specimens usually have beautifully colored iridescent and metallic eyes.

Feature Black Flies Horse Flies
Size 5 to 15 mm 1/4 to 1/2 inch
Body color Usually black Black to brown
Eyes Compound, large Iridescent, metallic
Wings Large, fan-shaped Varies

Distribution and Habitat

Black flies are known to have around 40 species in New Hampshire. They are adapted to various environments, including forests, meadows, and wetland habitats near running water, where their larvae can attach to submerged objects and feed.

Horse flies have over 100 species in Texas and are usually found near water sources, such as ponds and marshes, as this is where their larvae develop.

Diet and Feeding Habits

Black flies are known to feed on blood, attacking a variety of domestic and wild animals, including birds. In extreme circumstances, black fly bites can cause severe blood loss, leading to animal fatalities. At times, they linger around humans without biting but might crawl into the nose, ears, eyes, and mouth, becoming an annoyance.

Horse flies also feed on blood, biting animals such as livestock and causing them to swish their tails, twitch their flanks, and stamp their feet. It is worth noting that only 5% of adult stable flies near a horse will be on the animal at any given time.

Life Cycle and Breeding

Eggs and Larvae

Black flies lay eggs on submerged objects in fast-flowing water, while horse flies deposit their eggs on plants near moist areas. Larvae in both flies are aquatic:

  • Black fly larvae attach to submerged objects and feed on organic material.
  • Horse fly larvae are predators feeding on other insects and small organisms.

Pupae and Adults

Both black flies and horse flies undergo complete metamorphosis, including a pupal stage before emerging as adults:

  • Black fly pupae form in the same site as the last stage larvae or downstream, typically in the following spring or summer (source).
  • Horse fly pupae develop in semi-aquatic environments, and adults emerge from late spring to summer (source).

Breeding Sites

Breeding sites for black flies and horse flies often involve water, but the nature of the sites differ:

  • Black flies: fast-flowing water, usually associated with rivers or streams.
  • Horse flies: moist soil and vegetation, typically near standing water.

Mating and Courtship

Mating and courtship behaviors in black flies and horse flies can have unique characteristics:

  • Black flies: Mating may occur near the breeding site or take advantage of wind currents for mate encounters.
  • Horse flies: Females seek a blood meal for egg development, and males patrol territories, waiting for females.

Here’s a comparison table to sum up key differences:

Attribute Black Flies Horse Flies
Egg Laying Submerged objects in fast-flowing water Plants near moist areas
Larval Feeding Organic material Predatory
Pupal Stage Spring or summer Late spring to summer
Breeding Sites Fast-flowing water, rivers or streams Moist soil and vegetation
Mating Behavior Near breeding sites or on wind currents Males patrol territories, blood meals for females

Bites and Health Risks

Painful Bites and Reactions

Black flies and horse flies are two types of biting flies that can cause painful bites and health risks to humans and animals.

Black flies:

  • Small puncture wound at bite site
  • Swelling that can be the size of a golf ball
  • Reactions include headache, nausea, fever, and swollen lymph nodes in the neck1

Horse flies:

  • Larger and more robust flies2
  • Painful bite due to slicing mouthparts
  • Immediate burning sensation and lasting pain

Allergic Reactions

Some people may experience allergic reactions to the bites of both black flies and horse flies.

Common allergic reactions:

  • Swelling and redness around the bite area
  • Itching
  • Hives3

In rare cases, people may experience severe allergic reactions, such as anaphylaxis, which requires immediate medical attention.

Diseases and Parasites

While most biting flies, like mosquitoes, are known to transmit diseases, black flies and horse flies mainly cause discomfort and annoyance. However, they can still transmit certain diseases and parasites.

Black flies:

  • Can transmit a parasitic worm called Onchocerca volvulus in some regions, causing river blindness4
  • May also transmit other parasites, such as Mansonella, which can cause fevers

Horse flies:

  • Can transmit the parasitic worm Loa loa, causing loiasis5
  • Known to transmit diseases like anthrax and tularemia in animals, but rarely in humans
Black fly Horse fly
Small puncture wound Larger and more robust
Swelling Immediate burning sensation and lasting pain
Can transmit Onchocerca volvulus Can transmit Loa loa

In summary, black flies and horse flies are both types of biting flies that can cause painful bites, allergic reactions, and potentially transmit diseases and parasites. Generally, horse fly bites are larger and more painful, while black fly bites can cause swelling and severe reactions. It is essential to take preventive measures against these flies to protect yourself and your animals from health risks.

Bug Control Recommendation Tool

What type of pest are you dealing with?

How severe is the infestation?

Do you require child/pet/garden safe treatments (organic)?

Are you willing to monitor and maintain the treatment yourself?


Prevention and Treatment

Repellents and Sprays

  • Repellents can be effective in warding off both black flies and horse flies from humans and animals. Common ingredients include DEET, picaridin, and IR3535.
  • Permethrin-based sprays can also be used, particularly on clothing and gear for added protection. Note that permethrin is toxic to cats, so use with caution around feline pets.

Pros of repellents and sprays:

  • Effective in protecting against bites
  • Easy to apply

Cons of repellents and sprays:

  • May need to be reapplied frequently
  • Some people may have skin reactions to the ingredients

Protecting Livestock and Pets

  • For horses, use physical exclusion methods such as fly sheets, masks, and boots to keep the flies from accessing their face, legs, or body1. Fans in the stable area can also interrupt flight and prevent some flies from landing1.
  • For dogs and cats, consider spot-on treatments or oral medications that can help repel or kill flies. Consult your veterinarian for the best options for your pet.

Comparison Table: Black Fly vs Horse Fly Prevention

Prevention Method Black Fly Horse Fly
Repellents Effective Effective
Permethrin Sprays Effective Effective
Fly Sheets (horses) Helpful Helpful
Spot-on Treatments (pets) Varies Varies

Interesting Facts and Science

Pollination and Ecology

  • Some types of flies, such as the horse fly, play a role in the pollination of plants. They feed on nectar as adults and act as pollinators1
  • The tsetse fly does not participate in pollination but is a vital part of the African savanna ecosystem2

Various Types of Flies

  • Horse flies are known for their painful bite and typically feed on the blood of mammals^[3^]
  • Deer flies are similar to horse flies in size, feeding habits, and habitats4
  • House flies are common household pests and can spread diseases5

Example fly comparisons:

Fly Type Pollinator Habitat Blood Feeder
Horse fly Yes Marshes, open woods Yes
Tsetse fly No African savanna Yes
Fruit fly No Worldwide No
House fly No Worldwide No

Characteristics of some common flies:

  • Horse fly:
    • Robust and large, ranging from 3/8 to over 1 inch
    • Painful, blood-feeding bite[^6^]
  • Deer fly:
    • 3/8 to 1/2 inch long
    • Found in aquatic habitats such as marshes, ponds, and streams
    • Blood feeders like horse flies^[7^]
  • Fruit fly:
    • Small, with red eyes
    • Not a pollinator, but a common pest on fruit[^8^]
  • House fly:
    • Common worldwide
    • Not a blood feeder, but a major

Comparison and Conclusion

Black flies and horse flies are both biting insects that can cause discomfort to humans and animals alike. In this section, we will explore the key differences between these two types of flies and highlight their unique characteristics.

Size and Appearance

  • Black flies: Small, usually less than 1/4 inch long, dark-colored.
  • Horse flies: Larger, ranging from 3/8 to over 1 inch long, varying colors by species12.

Habitat

  • Black fly larvae develop in flowing, non-polluted water with high dissolved oxygen3.
  • Horse flies are found in various habitats, typically moist environments close to water4.

Bites

Both black flies and horse flies feed on blood, causing painful bites that can trigger allergic reactions in some people.

Control Methods

  • Physical barriers, such as fly sheets, masks, and boots can prevent flies from biting horses5.
  • Fans in stables disrupt fly flight patterns, reducing their ability to land and feed.

Comparison Table

Feature Black Fly Horse Fly
Size Small Larger
Color Dark Varies
Bite Pain Painful Painful
Habitat Flowing water Moist environments
Control Methods Physical barriers, fans Physical barriers, fans

In summary, black flies and horse flies differ in size, appearance, and habitat preferences. Both types of flies can cause painful bites, making them a nuisance to humans and animals. By understanding their unique characteristics and implementing appropriate control methods, we can minimize the impact of these biting pests.

Footnotes

  1. Black Flies – Purdue University 2 3 4 5
  2. Horse and Deer Flies – Purdue University 2 3
  3. Avoid bug bites – CDC 2
  4. Black Flies – Purdue University 2 3
  5. Horse and Deer Flies – Purdue University 2 3

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 – Western Black Horse Fly

Fly of some sort
Found this fellow in my backyard in residential Victoria BC. Was at least 2 to 2.5cm long. I’ve never seen one of these before but suspect it’s some sort of horsefly. Great site by the way.
Terry

Hi Terry,
You are correct. This is the Western Black Horse Fly, Tabanus punctifer. Females bite and drink blood from large mammals including man. Males, are identified by the eyes which appear to be joined at the top of the head. We turned to Eric Eaton for substantiation. Here is his response: “What a magnificent image! Wow. Would love to see this posted to BugGuide. It is a western horese fly, and a female. Males have holoptic eyes (essentially contiguous over the top of the head). Really fresh specimen. Thanks for sharing this one. Eric”

Letter 2 – Male Black Horse Fly

Subject: strange moth like bug?
Location: northern Virginia
July 18, 2016 12:12 pm
Hello! My mom and I noticed this bug on our outdoor umbrella and would like to know what it is. it’s a bit bigger than a grape, mostly black except for the eyes, which are sort of iridescent and translucent. it looks like a moth except for the eyes, which look like a fly’s. can you help?
Signature: signed, Julie

Male Black Horse Fly
Male Black Horse Fly

Dear Julie,
The close placement of the eyes indicates that this is a male Black Horse Fly,
Tabanus atratus.  There is a greater space between the eyes on the female Black Horse Fly.

Letter 3 – Male Black Horse Fly

Subject: I know it’s not a fly.
Location: Lebanon, IN. cornfield
July 26, 2016 8:34 pm
I’ve asked anyone and everyone. “It’s just a horse fly” , I know thats not it. This thing is so bizarre. It would fill a gatoraid cap perfect. Its all black with orange on the feet. Humungus grey orbs for eyes. I’d really love to know what it’s called. If I’m wrong, so sorry and thank you.
Signature: Laura Kniola

Male Black Horse Fly
Male Black Horse Fly

Dear Laura,
“Just a horse fly” is so dismissive of a magnificent family of flies, but this is in fact a male Black Horse Fly.  Male Horse Flies have enormous eyes with no space between them, which is an easy way to distinguish between the sexes.  Only female Horse Flies are blood-sucking biters, and they have a distinct space between their eyes.

Letter 4 – Male Black Horse Fly

Subject: Big cool fly
Location: Exeter, NH
August 19, 2016 5:45 am
Hi,
I saw this on my car this morning. I wanted to know what it was. Thank you.
Signature: Cheryl

Male Black Horse Fly
Male Black Horse Fly

Hi Cheryl,
This is a male Black Horse Fly,
Tabanus atratus.  According to BugGuide:  “Very wide range of habitats; generally near aquatic environments (Long 2001). Requires moist environments in which to lay eggs, and mammals to feed on (Long 2001). Larvae live ‘along the margins of ponds and ditches.'”  BugGuide also notes:  “Females feed on mammalian blood; males, which lack mandibles, feed on nectar and plant juices (Long 2001). Especially prone to attack cattle and other livestock.”  When livestock are not available, female Horse Flies will bite humans.  You can tell your individual is a male because of the large, close-set eyes.  Female Horse Flies have a space between their eyes.

Letter 5 – Male Black Horse Fly

Subject: Big Black Flying bug at night
Location: Kingsville, Tx
November 15, 2016 10:12 pm
I live in South Texas, Kingsville. This is the first time I have ever seen this kind of bug. It likes my yellow bug light, but goes crazy with a flash. Anyway, it is about 1-2 inch long. Sending a picture.
Signature: Marko

Male Black Horse Fly
Male Black Horse Fly

Dear Marko,
Your images are really underexposed and lacking in detail, but they definitely reveal that your visitor is a Horse Fly.  Once we lightened the image by adjusting the levels, we could see that the eyes are spaced closely together, indicating this is a male.  We believe you have a male Black Horse Fly,
Tabanus atratus, and the good news is that only female Horse Flies are blood-suckers.

Hey thanks guys. I’m glad it wasn’t a female. I already had enough bloodsucking ex wives. JK LOL or am I.

Letter 6 – Western Black Horse Fly

Subject:  Big biter
Geographic location of the bug:  Southern coastal BC Canada
Date: 07/21/2022
Time: 03:37 PM EDT
Your letter to the bugman:  Hi, I’ve seen a few of these just in the past 3-4 years. They like to land on the back of our horses and bite, leaving a small hole that draws blood. The are quite large and fly a bit like a big bumble bee, as if they are too heavy. No one around here knows what they are, and only see them a few times per summer! Any help would be great!
How you want your letter signed:  Regards

Western Black Horse Fly

This is a female Western Black Horse Fly which is pictured on BugGuide.  Female Horse Flies feed on the blood of horses, other livestock and wild animals, and when there is no preferred prey, they will bite humans.  Male Horse Flies do not bite.

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 – Western Black Horse Fly

Fly of some sort
Found this fellow in my backyard in residential Victoria BC. Was at least 2 to 2.5cm long. I’ve never seen one of these before but suspect it’s some sort of horsefly. Great site by the way.
Terry

Hi Terry,
You are correct. This is the Western Black Horse Fly, Tabanus punctifer. Females bite and drink blood from large mammals including man. Males, are identified by the eyes which appear to be joined at the top of the head. We turned to Eric Eaton for substantiation. Here is his response: “What a magnificent image! Wow. Would love to see this posted to BugGuide. It is a western horese fly, and a female. Males have holoptic eyes (essentially contiguous over the top of the head). Really fresh specimen. Thanks for sharing this one. Eric”

Letter 2 – Male Black Horse Fly

Subject: strange moth like bug?
Location: northern Virginia
July 18, 2016 12:12 pm
Hello! My mom and I noticed this bug on our outdoor umbrella and would like to know what it is. it’s a bit bigger than a grape, mostly black except for the eyes, which are sort of iridescent and translucent. it looks like a moth except for the eyes, which look like a fly’s. can you help?
Signature: signed, Julie

Male Black Horse Fly
Male Black Horse Fly

Dear Julie,
The close placement of the eyes indicates that this is a male Black Horse Fly,
Tabanus atratus.  There is a greater space between the eyes on the female Black Horse Fly.

Letter 3 – Male Black Horse Fly

Subject: I know it’s not a fly.
Location: Lebanon, IN. cornfield
July 26, 2016 8:34 pm
I’ve asked anyone and everyone. “It’s just a horse fly” , I know thats not it. This thing is so bizarre. It would fill a gatoraid cap perfect. Its all black with orange on the feet. Humungus grey orbs for eyes. I’d really love to know what it’s called. If I’m wrong, so sorry and thank you.
Signature: Laura Kniola

Male Black Horse Fly
Male Black Horse Fly

Dear Laura,
“Just a horse fly” is so dismissive of a magnificent family of flies, but this is in fact a male Black Horse Fly.  Male Horse Flies have enormous eyes with no space between them, which is an easy way to distinguish between the sexes.  Only female Horse Flies are blood-sucking biters, and they have a distinct space between their eyes.

Letter 4 – Male Black Horse Fly

Subject: Big cool fly
Location: Exeter, NH
August 19, 2016 5:45 am
Hi,
I saw this on my car this morning. I wanted to know what it was. Thank you.
Signature: Cheryl

Male Black Horse Fly
Male Black Horse Fly

Hi Cheryl,
This is a male Black Horse Fly,
Tabanus atratus.  According to BugGuide:  “Very wide range of habitats; generally near aquatic environments (Long 2001). Requires moist environments in which to lay eggs, and mammals to feed on (Long 2001). Larvae live ‘along the margins of ponds and ditches.'”  BugGuide also notes:  “Females feed on mammalian blood; males, which lack mandibles, feed on nectar and plant juices (Long 2001). Especially prone to attack cattle and other livestock.”  When livestock are not available, female Horse Flies will bite humans.  You can tell your individual is a male because of the large, close-set eyes.  Female Horse Flies have a space between their eyes.

Letter 5 – Male Black Horse Fly

Subject: Big Black Flying bug at night
Location: Kingsville, Tx
November 15, 2016 10:12 pm
I live in South Texas, Kingsville. This is the first time I have ever seen this kind of bug. It likes my yellow bug light, but goes crazy with a flash. Anyway, it is about 1-2 inch long. Sending a picture.
Signature: Marko

Male Black Horse Fly
Male Black Horse Fly

Dear Marko,
Your images are really underexposed and lacking in detail, but they definitely reveal that your visitor is a Horse Fly.  Once we lightened the image by adjusting the levels, we could see that the eyes are spaced closely together, indicating this is a male.  We believe you have a male Black Horse Fly,
Tabanus atratus, and the good news is that only female Horse Flies are blood-suckers.

Hey thanks guys. I’m glad it wasn’t a female. I already had enough bloodsucking ex wives. JK LOL or am I.

Letter 6 – Western Black Horse Fly

Subject:  Big biter
Geographic location of the bug:  Southern coastal BC Canada
Date: 07/21/2022
Time: 03:37 PM EDT
Your letter to the bugman:  Hi, I’ve seen a few of these just in the past 3-4 years. They like to land on the back of our horses and bite, leaving a small hole that draws blood. The are quite large and fly a bit like a big bumble bee, as if they are too heavy. No one around here knows what they are, and only see them a few times per summer! Any help would be great!
How you want your letter signed:  Regards

Western Black Horse Fly

This is a female Western Black Horse Fly which is pictured on BugGuide.  Female Horse Flies feed on the blood of horses, other livestock and wild animals, and when there is no preferred prey, they will bite humans.  Male Horse Flies do not bite.

Reader Emails

100431

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 – Horse Fly from Pennsylvania

 

Horse FlySubject:  Flying insect
Geographic location of the bug:  Pennsylvania
Date: 08/08/2022
Time: {current_time} EDT
Your letter to the bugman:
Fly or a bee? We’re unsure what this is.
How you want your letter signed:  NA

Horse Fly
Horse Fly

Dear NA,
This is a Horse Fly, and a female, the blood sucking sex in the family.  We are not certain of the species.  While Horse Flies do not normally prey upon humans, they are opportunistic if other preferred prey, including livestock and deer, are not available.  The bite of a Horse Fly is reported to be quite painful on the rare occasions where a human is bitten.

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.

    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: Horse Fly

Related Posts

1 Comment. Leave new

  • Are western black flies dangerous. Should I kill them or let them be? I saw one today on a weed and would not leave even when I bent the leaf down so I could get a better look at it. I left it alone but I have dogs and cats. Are they harmful to them ?

    Reply

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

keyboard_arrow_up