If you've ever dealt with horse flies, you know their bites can be painful. But are horse fly bites harmful to you or your pets? And what can you do to help ensure you don't get bit?
What Is A Horse Fly?
Horse flies resemble large house flies. They are black and brown in color and have iridescent eyes. Some horse flies have transparent wings while others have very dark, almost black, wings. These flies can range in size from .75 inches to 1.25 inches long.
Why Do Horse Flies Bite?
Female horse flies feed on blood. Like female mosquitoes, female horse flies require a protein meal to produce the eggs that will grow into the next generation of horse flies.
Also like mosquitoes, horse flies feed using special mouthparts. However, unlike mosquitoes, which puncture their victim's skin and suck blood through their mouthparts, horse flies are equipped with slicing stylets. Using these tiny blades, horse flies cut open their victim's flesh and drink from the blood that pools in the wound. These bites can result in irritation and swelling.
Horse flies are diurnal, meaning they are active during the day. They prefer to feed on livestock, like cows and horses, hence their name. This can be troublesome as horse flies can carry pathogens that can cause disease in some livestock, which can result in potential economic loss. And unfortunately, horse flies have no issue feasting on humans or pets as well, if given the opportunity.
How to Treat a Horse Fly Bite
According to Healthline, if you've been bitten by a horse fly, first clean the affected area and then treat the bite with an over-the-counter antibiotic ointment or spray to help reduce swelling, pain and irritation.
Healthline then advises for you to monitor the bite for any signs of infection, such as pus and/or a foul odor, and to seek medical attention right away if you notice any unusual signs. This is especially true if you experience more severe signs, like difficulty breathing, a rash or worsening pain.
How to Help Get Rid Of Horse Flies
Horse flies can be rather tricky to get rid of, especially in rural areas where livestock is present. Female horse flies are willing to travel great distances for their feast. If you happen to be around an area where horse flies are a problem, using repellents containing DEET can help provide protection, according to the University of Kentucky College of Agriculture, Food and Environment. If you have a barn or other area where you keep pets or livestock, you can take a few precautions to help keep horse flies at bay. Screen in any animal shelters to help keep horse flies out.
Entomologists with the Agricultural Extension at the University of Missouri have published instructions on how to build several different horse fly traps. Also, make sure to eliminate any standing water, as horse flies prefer to lay their eggs in moist environments. Marshes and swamps are particularly susceptible to horse fly infestations.
Finally, consult with a veterinarian regularly to help keep your animals healthy.
As the weather warms up the UK is often swarmed with reports of biting horseflies. A Museum fly expert explains what is going on.
Often large, persistent and painful, a bite from a horsefly is an experience unlikely to be forgotten. But why do horseflies seem to appear more in the summer months?
Horseflies tend to be more active during heatwaves. Yet it might not be that there are more horseflies than usual out for blood, but simply that there are more people outside, enjoying the summer.
More people out and about in the warm weather, exposing their skin, will increase the likelihood of people being bitten by the flies (some of which are also called clegs). Coupled with the ubiquity of reports from newspapers to social media, this can make it look like it is a bumper year for the insects.
Why horseflies bite
Not all adult horseflies bite - only the females have mouthparts able to break the skin and feed on blood. This is because only the females need a blood meal.
Dr Daniel Whitmore, Senior Curator of Diptera and Siphonaptera at the Museum, explains, 'They need a high protein input to help develop their eggs after fertilisation.'
The males don't make eggs, so they don't need blood.
Horsefly saliva prevents the blood from clotting. ©IanRedding/ShutterStock
The way that horseflies feed on blood can seem brutal when compared to the precision of a mosquito. A pair of serrated mandibles saw into the skin, cutting until they break small vessels and the blood begins to flow. An anticoagulant in the fly's saliva then prevents the blood from clotting as the insect sucks up its meal.
While mosquitoes release a mild anaesthetic, horseflies don't - which is one of the reasons their bites are so painful. The fact that they cut into the flesh rather crudely only adds to this pain.
'The horsefly bite is much less sophisticated, likely because usually they have to pierce through much tougher skins than ours when they are feeding on a cow or a horse,' says Daniel. These are horseflies' more usual food source, but they will home in on any large mammal they detect.
Do horsefly bites sting?
In most cases, a bite will result in a raised, red area of skin, which might be painful and sensitive to touch. In extreme cases, bites can cause an allergic reaction that can result in dizziness, swelling and fluid-filled blisters that become infected. If that happens, it is recommended that you seek medical advice.
How to spot and identify a horsefly
The easiest way to spot a horsefly is by looking at its overall size. The insect tends to be large compared to other biting flies, often with colourful and patterned eyes. In males the eyes are so big they touch at the top of the head.
Not all horseflies are dependent 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 damp soil. All feed on other invertebrates until ready to pupate and emerge as adults.
This means you're more likely to come across the larvae around bodies of water, although the adults will disperse. Farms are frequently a hotspot for these flies, as they are attracted by cattle and horses.
Male horsefly, with eyes touching at the top of its head. ©Mark Robinson/Flickr CC BY-NC 2.0
One of the easiest ways to avoid being bitten is to cover up. But according to Daniel, even this might not be 100% effective.
'Horsefly females have such strong, powerful mouthparts that they can sometimes bite you through your clothes,' he says. 'But obviously they are more likely to go for bare skin.' It's probably best to opt for loose-fitting clothing.
There is also evidence that the flies home in on their next victim by sniffing out exhaled carbon dioxide. This means that those doing more strenuous outdoor activities could be at greater risk of being bitten.
Horseflies in the UK
'Obviously, bloodsucking species are annoying,' says Daniel, but he emphasises that they play a vital role in the ecosystem.
In the UK there are just 30 species of horsefly, but globally there are over 4,500 species whirring around every part of the world except the polar regions.
As the female horseflies seek out their next blood meal, the males are searching for something much sweeter. Buzzing from flower to flower, the male flies actually feed on nectar.
In some cases, this makes the flies crucial pollinators, coevolving with the plants on which they feed.
Horseflies can be identified by their colourful eyes. ©Magre Flåten/Wikimedia Commons
'There are some species of horsefly in which both sexes have extremely elongated mouthparts to suck nectar out of long-tubed flowers,' explains Daniel.
So entwined is this relationship that the flies are thought to be involved in driving new species of flowers to evolve, and vice versa.
Along with many other flying insects, horseflies are also a key food source for many other animals higher up the food chain. They help underpin other, more charismatic species such as bats and birds, while the aquatic larvae of the insects feed fish.
So even though horseflies might plague us in the UK during the summer months, they're an important aspect of the much wider ecosystem.