A horsefly is a large insect that will bite you at the first opportunity. They are 1.3 to 2.5 cm long, triangular and carnivorous. When they bite, they take out a piece of meat and inject poison. The area around the horsefly bite will be sore for about five days. Horseflies are also important vectors of diseases such as leukocytosan disease of turkeys.

Species origin and description

Photo: horsefly

Photo: horsefly

Horsefly is a representative of the horsefly insect family (Diptera order), or rather, a representative of the horsefly genus. These fat flies, about the size of a housefly or the size of a bumblebee, are sometimes referred to as green-headed monsters. Their metallic or iridescent eyes occur dorsally in the male and separately in the female.

Their mouth resembles a wedge-shaped miner’s tool. Other names for the insect are bat and bat ear. One of the most common species (Tabanus lineola) has bright green eyes and is known as the green head. The goldeneye genus, commonly known as the deer fly, is slightly smaller than horseflies and has dark wing markings.

The numerous, painful stings of large populations of these flies can reduce milk production in dairy and beef cattle and interfere with cattle grazing and horses, as attacked animals will gather together. Animals can even get hurt while running away from these flies. In this case, blood loss can be very significant.

Video: horsefly

These big flies with strong body — powerful and agile, circling around or pursuing their target with humiliating persistence to make painful injections into the skin and suck the blood. The flies only stay in contact with the host for a few minutes, and then they leave until they need to eat again, which happens every 3-4 days.

Serious allergy to a horsefly sting is not common, but it can be signaled by additional symptoms:

  • feeling dizzy and weak;
  • shortness of breath;
  • temporarily swollen skin, for example, around the eyes and lips.

More severe allergies are rare, but are urgent.

Ambulance should be called for any signs of anaphylaxis, which include:

  • swelling, itching, or rash;
  • face, lips, hands, and feet are likely to swell;
  • swelling of the throat and tongue are dangerous symptoms;
  • nausea, vomiting, or diarrhea;
  • difficulty swallowing or breathing.

Appearance and Features

Photo: What a horsefly looks like

Photo: What a horsefly looks like

Horsefly is a dark gray fly with gray-brown speckled wings and bizarre striped iridescent eyes. Adult flies are brownish, hairy, robust, about 1.7 cm long, superficially resembling honey bees, except they have only one pair of wings. There are faint smoky spots on the horsefly’s wings.

Fully grown larvae are 0.6 to 1.27 cm long and have dense yellowish-white to pinkish thick skin. They are blunt at one (posterior) end and taper towards the other (anterior) end, which has a pair of robust, hook-shaped mouthparts. Each segment of the body is surrounded by strong spines. The antennae of horseflies have five segments and are thick at the base, becoming thinner with each segment. These antennae are long and thin. The wings of horseflies are usually completely dark or completely transparent.

Fun Fact: The easiest way to spot horsefly — look at its overall size. The insect tends to be large compared to other biting flies. Males have eyes so large they touch the top of their head.

Not all horseflies depend on water, but many species lay their eggs on plants growing near ponds, rivers, and streams. The larvae of some species are aquatic, while others live in moist soil. All feed on other invertebrates until they are ready to pupate and become adults. This means that you are more likely to encounter larvae around water bodies. Farms are often a hotspot for these flies, as they are attracted to livestock and horses.

Now you know what happens when a horsefly bites. Let’s see where this insect lives.

Where does the horsefly live?

Photo: Horsefly Insect

Photo: Horsefly Insect

Horseflies tend to live in forests. The species usually feed during the daytime and are most visible on calm, hot, sunny days. They are commonly found in both suburban and rural areas near reservoirs that serve as breeding grounds and where mammalian hosts are most numerous.

The larvae develop in the gastrointestinal tract of host animals during the winter. In late winter and early spring months, adult larvae are found in the host’s feces. From there they burrow into the soil and form a puparia from the skin of their last stage (instar) larvae. They develop into adult flies inside the puparium and appear after 3-10 weeks.

Adults are active from mid-summer to autumn. Adult females lay eggs on the hair of horses, especially on the hair on the front legs, as well as on the abdomen, shoulders and hind legs. The eggs hatch in 10 to 140 days with the proper stimulus (moisture, heat and friction) caused by the horse licking or biting the egg-infected hair.

Tiny first stage (instar) larvae enter the mouth and burrow into the tongue for about 28 days before they molt and move to the stomach where they remain for 9-10 months, developing into the third stage after about 5 weeks. One generation of horseflies grows in a year.

What does a horsefly eat?

Photo: Great Horsefly

Photo : Great Horsefly

Adult horseflies usually feed on nectar, but female horseflies require blood before they can reproduce effectively. The bites of female horseflies, especially large ones, can be quite painful because their mouthparts are used for tearing and grinding, unlike mosquitoes, which simply pierce the skin and suck blood. They have serrated, saw-like teeth that cut through exposed skin, then release an anticoagulant to stop blood clotting while they enjoy their meal.

Fun fact: Female horseflies require up to 0.5 ml of blood to reproduce, which is a lot compared to their size. They can draw about 200 mg of blood in a few minutes.

Horsefly bites can develop into large, red, itchy, swollen bumps within minutes. Some people also report feeling hot, weak, and nauseous. For most, they are absolutely harmless, but extremely inconvenient. In exceptional cases, some people may suffer from an allergic reaction with symptoms such as dizziness, wheezing, difficulty breathing, a patchy skin rash, and severe swelling that may be visible on the lips or tongue.

Horseflies are intermittent feeders. Their painful stings usually elicit a response from the victim, so the fly is forced to move to another host. Therefore, they can be mechanical carriers of some animal and human diseases. The female horse flies are also persistent and will generally continue to bite the host until they either succeed in acquiring their blood meal or are killed. They have even been known to pursue their intended goals for short periods of time. Some species carry disease-causing organisms, but most fly-borne diseases are associated only with livestock.

When outdoors, wear light-colored clothing and insect repellent to prevent horsefly bites. If they enter structures, exclusion is the best method of control, including checking all doors and windows.

Character and Lifestyle Traits

Photo: Bull Horsefly

Photo: Bull Horsefly

Adult horseflies — fast, strong fliers capable of flying over 48 km, although they do not usually spread widely. Most often they attack moving and dark objects. Horseflies often rest on paths and roads, especially in forested areas where potential owners are waiting for them. Flies are attracted to light and sometimes congregate in windows. Horseflies are more common in hot, sunny weather with little wind, such as during midsummer daytime. They can become more of a pest when thunder accompanies hot weather.

Horseflies are diurnal, meaning they are active during the day. They prefer to feed on the blood of livestock such as cows and horses. This can be problematic as horseflies carry pathogens that can cause disease in some livestock species, which can lead to potential economic losses. And sadly, horseflies have no problem feasting on people or pets, if given the opportunity.

Fun Fact: Like other blood-sucking insects such as mosquitoes, female horseflies use both chemical and visual cues to locate their hosts. Carbon dioxide emitted by warm-blooded animals provides a long-range signal to attract flies from a distance, while visual cues such as movement, size, shape, and dark color serve to attract horseflies at shorter distances.

Social structure and reproduction

Photo: Large horsefly

Photo: Large horsefly

Horseflies undergo complete metamorphosis, which includes going through 4 complete life stages. These are egg, larva, pupa and adult stages. Females lay batches of 25 to 1000 eggs on vegetation that stands above water or wet areas. The larvae that hatch from these eggs fall to the ground and feed on decaying organic matter or small organisms in the soil or water.

Horsefly larvae develop in mud along pond edges or stream banks, wetlands, or seepage areas. Some of them are aquatic, and some develop in relatively dry soil. The larval stage usually lasts one to three years, depending on the species. Mature larvae crawl to drier areas to pupate, and eventually adults emerge. The duration of the pupal stage depends on the species and temperature, but can vary from 6 to 12 days.

It is difficult or almost impossible to find and eliminate horsefly breeding grounds. They breed in ecologically sensitive wetlands, so there is concern about the impact of drainage or insecticide application on non-target organisms or water supplies. In addition, these insects are strong fliers that can move from some distance. Breeding areas can be very extensive or some distance away from where problems occur.

Fortunately, horseflies are sporadic problems at certain times of the year. Some adaptation in behavior or the use of repellents may allow outdoor enjoyment.

Natural enemies of horseflies

Photo: What a horsefly looks like

Photo: What a horsefly looks like

Along with many other flying insects, horseflies are also a key food source for many other animals higher up in the food chain. They help support other species such as bats and birds while aquatic insect larvae feed on fish.

Birds that feed on horseflies:

  • Black-headed cardinals are songbirds with large, conical, thick beaks. Their color depends on the sex of the bird: the fiery male has an orange cinnamon body with a black head and black and white wings, while immature males and females are brown with an orange chest patch. They prey on various insects, including horseflies and caterpillars. Black-headed cardinals can be found mainly in the western United States in thickets and forest edges, as well as in yards and gardens;
  • Sparrows are among the most common birds in North America and are seen mostly in flocks. It is known that if there are insects in the garden, including horseflies, then sparrows can be a nuisance to your home if they are overpopulated. They build their nests in the walls of the house, destroying the forest. Their feces can also pose a risk to human health. Despite this, they can be of great importance in reducing the population of horseflies around houses;
  • swallows feed mainly on insects, as well as grains, seeds and fruits, and live near fields and areas with an abundance of flying spaces and a natural supply of water . They are fast-flying songbirds that range in color from pale brown to blue-white and are found in much of North America. Flying insects such as horseflies are the main food source for swallows;
  • warblers — insectivorous birds that feed on spruce buds and horseflies. Their population often fluctuates in proportion to the population of the insects they eat. There are about 50 different types of warblers. They are small songbirds with white underparts, green backs and white eye lines. Juvenile warblers are dark green with a distinctive pale eyeline and pale yellow underparts.

Population and species status

Photo: horsefly

Photo: horsefly

The horsefly population grows in sweltering weather. Mostly in warm, humid and calm weather, they become a real plague for horses and their owners. There are over 8,000 different species of horseflies in the world, all related to each other. Against horseflies I use various methods of struggle.

Unfortunately, there are few methods to control horseflies and minimize their bite. The risk of biting can be reduced, but there are currently no known ways to completely eliminate it. As with most other insect infestations, prevention is the first line of defense against horseflies in the home. Good sanitation and house cleaning can prevent horsefly infestations as their larvae tend to develop in decaying organic matter. Installing a screen on doorways and windows can also prevent flies from entering the premises and settling in the house.

Horsefly traps exist, but their effectiveness varies. The traps consist of a large dark sphere moving back and forth, often sprayed with some kind of animal musk or similar inviting fragrance. This sphere is located below a bucket or similar container containing a sticky flytrap – horseflies attracted to the sphere fly up and ideally land on the tape. Draining any standing bodies of water around the property can also help to minimize the risk of horsefly infestation.

If you’ve already found an infestation of horse flies in your home, preventative measures will be of little use. Natural methods for dealing with horsefly infestations include fly paper and fans. Horseflies are bothered by smoke, so burning candles can also encourage them to leave the home they have settled in. However, these measures are at best marginally effective in removing horsefly infestations. The use of pesticides can also be moderately successful in controlling horsefly populations.

Gidflies are large flies. Although adult males primarily drink nectar and plant juices, female horseflies require protein to produce eggs. Blood is the source of this protein, and horseflies can get it from horses, cows, sheep, rabbits, and even humans. The bite of a female horsefly is felt immediately, creating a red bump.

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