11 Facts about Horsefly: It Can Spread Diseases and Hurt Your Pets

Horsefly (Tabanidae), popularly known as the green-headed monster, is the largest fly species. This invertebrate is aggressive and they can bite you for blood. There are around 3,000 species of horseflies in the world. Let’s have a look at the horsefly facts below.

Scientific name: Tabanidae
Kingdom: Animal
Class: Insects
Order: Diptera
Phylum: Arthropod

1. Horseflies are everywhere

Except for Arctic, Antarctica, and a few islands, such as Hawaii, horseflies can be found almost wherever on the planet. Although they can live in a wide range of habitats, they still prefer warm, moist environments for reproducing. Horseflies don’t like the shadow and do not work at night. They prefer to fly in the sunbeam. Horseflies are only found outside; they do not eat or seek shelter indoors. How lucky we are! Horsefly season lasts from May to September.

2. Horsefly appearance

Horseflies are considered “real flies”, which means they only have one pair of wings with balancing halteres at the base of their wings. Due to the halteres, horseflies can fly acrobatically. They’re pretty big with the measure of 3/4 – 1.25 inches. 

Their heads are enormous in comparison to the rest of their bodies. Horseflies have hairs all over their bodies, except for the tip of their antennas. Their legs include claws that allow them to grasp their prey.

Horseflies are also distinguished by their huge and multicolored eyes. When observed in certain lights, these massive compound eyeballs can be vividly colored or exhibit iridescence. Male horseflies can be distinguished from females by the fact that their eyes are practically touching, but females’ eyes are apart.

This type of fly comes in different colors, from blackish, and dark grey to yellowish-brown. The wings are either clear or a hazy gray or brown color. Different species can be distinguished by subtle variances in their heads, the colors, patterns on their bodies, and the vein patterns on their wings.

Horsefly babies, often known as maggots, are long (about 10 to 30 millimeters) and tapered at the head end. They come with a retractable head and are found in wet or moist environments. They range in size and are found in wet or moist environments.

3. Horsefly and deerfly

Horseflies are frequently mistaken for deerflies, which are members of Tabanidae. They bite humans. too. Although having many in common, they are still distinguishable. Let’s have a look at those differences:

  • Horseflies are far larger than deerflies with a length of 0.5 – 1.25 inches. Whereas deerflies are about 0.25 – 0.33 inches.
  • While the deerfly’s antennae are long and thin, the antennae of the horsefly are shorter and thick.
  • Deer flies ( genus Chrysops) are about 10 mm long. They have striped abdomens, yellow to black bodies, and very thin wings with dark patches. Horse-flies (genus Tabanus), on the other hand, are bigger (up to 25 mm (1 in) long). They mostly have metallic luster, dark or black color with dark eyes.

Horsefiles and deerflies together

  • The horsefly’s wings are clear or foggy, whereas the deerfly’s wings are clear with dark spots or lines.
  • Deerflies exclusively bite moving animals, but horseflies don’t care whether the animal is moving or not, they bite anyway.
  • You can know a deerfly is coming by its sound, while the horsefly is much more quiet.
  • Most horseflies prefer the legs, ankles, or backs of the knees of their victim, whereas deerflies prefer the nape of the neck, head, and shoulders.
Fun facts: There are about 4,000 species in the Tabanidae family and they can be found almost everywhere on the planet. Tabanids are also referred to as clegs and gadflies. And the term “gadfly” is now more commonly used to describe an obnoxious person who continuously criticizes.

4. Horsefly can bite you

Male and female adult horseflies consume nectar and other plant liquids. Some horseflies are actually significant pollinators for some plants. However, the females need to eat blood for their reproduction. That’s why they need to bite animals and humans.

In the hunt for prey, the female horsefly is similar to a female mosquito. She is attracted to prey with dark fur or clothing, the carbon dioxide they expel, the texture and temperature of their skin, the sweat, and even shiny objects. The majority of horseflies favor large creatures such as horses, buffaloes, or even people. They do, however, prey on other small mammals, rodents, and even cold-blooded animals like lizards. If needed, they will even eat a recently dead animal. 

Sometimes you don’t know when a mosquito bites you until it’s itchy. However, that feeling is not gonna like that in the horsefly bite. When a horsefly bites you, the pain will come immediately. Horseflies, unlike mosquitoes, shred the victim’s skin and drink blood rather than pinching and sucking blood. 

A horsefly is biting people

Females’ mouth parts consist of a pair of mandibles and a pair of maxillae. This scissor-shaped jaw will tear the skin and break the blood vessels beneath it. The sponge-like tongue will lock in and suck the blood. When sucking blood, the female horsefly injects an anticoagulant to prevent it from clotting. As the result, you will feel a strong burning sensation when being bitten by a horsefly.

When the horsefly has identified possible prey, she will relentlessly pursue them. If she’s pushed away, she’ll return to finish the meal. If she is not prevented, she will bite from prey to prey. And that’s how the disease is spread. Horseflies are lonesome attackers, but some work in groups when necessary. Horsefly infestations are very harmful.

Horsefly bites look like this

Horsefly babies (maggots) are ferocious predators as well. They live in wet soil and in lakes or ponds of fresh and saltwater. They prey on insect larvae, tadpoles, toads, and frogs (if they fit their mouths). Furthermore, the larvae appear to be poisonous, as prey is weakened after being bitten.

Facts: Horseflies can bite your pets like cats and dogs; and transfer bacteria and other blood pollutants. Horse fly bites are most common in larger dog breeds, and the most vulnerable parts to be bitten are the abdomen, legs, and neck.

5. Horseflies can spread diseases

Horsefly bites are not only irritating but also dangerous. It has the potential to make you sick by spreading pathogens like anthrax. Female horsefly bites are extremely painful, but these insects can also transmit bacteria and blood pollutants from one host to another. They can cause severe illness in livestock and people, as well as lower growth rates and milk supply in cattle. If a bitten person or animal develops an allergy, the effects are aggravated.

Their saliva can also cause inflammation, swelling, sepsis, itching, and bruises near the spot. A horsefly bite can occasionally cause an allergic reaction:

  • Swallowing and breathing difficulties
  • Swelling of the face or mouth
  • Abdominal or chest pain
  • Red skin
  • Vomiting 
  • Blacking out

You can soothe a horsefly bite by doing:

  • Cleanse the area.
  •  Apply a cold towel or ointment to the wound to reduce redness and itchiness.
  • Take an antihistamine to reduce/stop itching (if you need it).

Be cautious because you may exhibit indicators of an infection like swelling, redness increasing, heavy mucus, bad smell, and other strange symptoms. If you encounter any of the following serious symptoms, this is an emergency:

  • Can’t breathe, wheezing 
  • Face or mouth swellings
  • Can’t swallow
  • Being blue

6. Horsefly Predators

Horseflies can be eaten by birds, wasps, and other flies-eating predators. A wasp known as the horse guard wasp feeds horseflies to her kids. She disables the horsefly and returns it to the nest, where her larvae will consume it alive.

How about the horsefly eggs? Those eggs are parasitized by some parasitic wasp’s eggs, eaten by birds and other animals, attacked by tachinid flies and tiny worms called nematodes, and are vulnerable to fungus.

7. Horseflies are one of the fastest insects

Horseflies are one of the fastest flying insects all over the world. According to the record, a male horsefly Hybomitra hinei wrighti has been reaching speeds of up to 145 kilometers per hour (90 miles per hour) when chasing a female. An amazing speed for a fly!

Horseflies are fast, strong fliers that can travel more than 30 miles. They sometimes swarm along routes and roads in wooded regions, waiting for prey to pass by.

You may read some other Word’s fastest flying bug articles:

  1. Hawk moths
  2. Hornets
  3. Bees
  4. Ladybugs
  5. Dragonflies
  6. Skippers

8. They are active during the day

Most horseflies do not fly far from their home, while some can travel up to 40 kilometers. The insects do not attack at night because they are diurnal, not nocturnal. They like the sunlight, that’s why they bite less on cloudy, chilly, and windy days. Like hawk moths, horseflies are drawn to lights (street lights or porch lights) and can occasionally gather in large groups to fly around them.

9. Types of horseflies

Horsefly is a member of the Tabanus genus which includes more than 1300 species and hundreds of subspecies. Here are some of them:

Black horsefly (Tabanus Areatus) can grow to be 20-25 mm long. The flies might be completely black or they can be dark brown to blackish purple. The female Tabanus atratus have dichoptic (separated) eyes, whereas males have holoptic (continuous) eyes.

Pale giant horsefly (Tabanus bovinus) favors bovine animals as a source of blood, as its scientific name implies. However, it may bite other types of mammals as well. It bites less than deer flies (Chrysops). It is a quick and skilled flier that can easily escape most attempts to swat it. For a horsefly, this species is relatively large, about 25–30 mm long.

Narrow-winged horsefly (Tabanus maculicornis) can grow to be 12–13 millimeters (0.47–0.51 in), which is quite small. It has a dark body, a head with a greyish supraoccipital border, and green eyes. Males have a broad purple band around their eyes, while females have a coppery luster and a single purple band.

Western horse fly (Tabanus punctifer) measures 20.5 mm (0.8 in) in length. The thorax is coated in long hairs which is creamy white, whereas the abdomen is entirely black. They are most commonly seen in the southern and western areas of the US.

Green-eyed horsefly (Tabanus fulvulus) comes with outstanding green eyes as its name.

10. Life cycle of a horsefly

Horseflies begin reproducing shortly after emerging from their pupae. Male horseflies may travel to the top of the hills and woodland in search of females. Female horseflies may only breed once in their lives.

A male chases her when one passes. If the female agrees, they’ll mate for 30 minutes. This only occurs when the weather is warm and sunny. The female will lay her eggs after completing sucking a blood meal.

– Egg:

Horseflies lay their eggs in groups (from 100 to 1000 individuals), on the undersides of leaves, the vertical surfaces of aquatic plants, sticks, or rocks near lakes or ponds…, while the male watches from a nearby location. When the eggs are first laid, they are cylindrical in shape and creamy white in color, but they quickly darken and turn gray or black. Horsefly eggs hatch in five to seven days, depending on the environmental circumstances.

– Larvae: 

After hatching, the horsefly (depending on the type) undergoes the first of six to thirteen distinct larval phases, which can be aquatic, semi-aquatic, or terrestrial. Most horsefly species overwinter in their last larval phase, which turns into a pupa as spring arrives.

When submerged in water, the larvae can receive air via a respiratory siphon near the hind end. The horsefly larvae are carnivorous. They eat insect larvae, worms, and arthropods.

Horseflies try to suck blood and lay eggs on horse

– Pupae: Horse fly pupae are long and brown. They are rounded in the front end and tapering in the back end. This pupal stage can last 3 to 6 weeks before the adult appears.

– Adult: After the pupal stage, the adult horsefly which is usually male appears. 

A horsefly maggot’s whole life cycle, including molts and pupation, can last up to three years. The mature horsefly, on the other hand, only lives for a month or two. Each year, one generation is born.

Horseflies like water, they are drawn to bodies of water to breed and eat. The females frequently lay their eggs on aquatic plants and will wait for host animals (such as horses and cattle) to enter their bodies. Adult female flies will occasionally attempt to lay eggs on host animals.

Larvae develop in the digestive systems of host animals after entering the host body, damaging the tongue, lips, stomach lining, and intestine. When the time comes, fully grown larvae can be seen in the stool of the host. They burrow into the ground from there and create pupae from their last phase larval skin. Inside the pupae, they develop into an adult and emerge in 3 to 10 weeks. Adult horseflies are active from mid-summer to the end of the season.

11. How to prevent horseflies

You can try some horse fly deterrents below to prevent them from bitting:

  • Set up screens
  • Horsefly repellent
  • Horsefly trap: Sticky paper and traps
  • Chemical control

To know details about how to repel horseflies, you can follow our guidelines.


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