As lovely as summer is, it can also bring a number of health hazards – from sunburn and dehydration to garden pests and insect bites. We’ve previously written tips for keeping wasps and ticks at bay. But another common pest to look out for in the summer are horseflies.
Due to their scissor-like mouthpieces, horseflies are known for delivering bites that are more painful than other bugs. While horses and other dark-coloured mammals are their main targets, horseflies can bite humans too. Luckily, these bites aren’t usually dangerous – but they can be painful, so it’s best to do what you can to avoid being bitten.
With that said, here’s everything you need to know about horseflies, and how to protect yourself and your pets.
What are horseflies?
Horseflies are a type of flying insect that belong to the Tabanidae insect family. There are over 4,500 horsefly species worldwide, however, only 30 of these are found in the UK.
Female horseflies have sharp mouthparts, which they use to feed on large mammals. They rely on blood to survive and reproduce because it contains a certain protein they need to develop their eggs. In fact, female horseflies need up to 0.5ml of blood to reproduce – which is a large amount considering their small size – and can consume around 200mg of blood in just a few minutes.
Male horseflies, on the other hand, don’t have sharp mouthparts and only feed on flower nectar.
As their name suggests, horseflies feed mainly on large, dark-coloured animals – and horses are their prime target. However, this doesn’t stop them from biting humans if they get the chance. Horseflies mate during the summer, which makes humans outside enjoying the sunshine an ideal snack – and they’re often able to land undetected.
Not all horseflies rely on water to survive, but many species lay their eggs on plants growing near rivers, ponds, and streams. The larvae of some species can survive in water and others live in damp soil. All feed on snails, earthworms, and other invertebrates until emerging as adults.
As a result, you’re most likely to find horseflies near bodies of water. Other common areas include damp woodlands, long grass, meadows, stables, and grazing fields. According to Northumberland Wildlife Trust, peak horsefly season is between May and September.
What do horseflies look like?
There are 30 species of horsefly in the UK and the most common is the Notch-horned cleg-fly.
Notch-horned cleg-flies are dark grey in colour, with grey-brown mottled rings and striped eyes.
Horseflies vary in size, depending on their species, but are generally larger than most houseflies – often measuring between six and 20 millimetres long. The Notch-horned cleg-fly is one of the smaller species.
You can learn more about different species of horsefly found in the UK on the Nature Spot website.
What are the symptoms of a horsefly bite?
Horsefly bites tend to be more painful than other insect bites. This is because of the method that the flies use to bite. So, if you’ve been bitten by a horsefly, you’ll probably know about it.
Horseflies have strong, sharp mouthparts that work like serrated scissors on the skin of animals and humans. While drinking the blood, the fly anchors to the skin using small hooks along its mouthparts and releases an anticoagulant to stop blood from clotting. While this can be painful enough in itself, unlike ticks and mosquitoes, horseflies don’t inject any type of anesthetic when they bite either. They also don’t leave behind a stinger or mouthpart.
Symptoms of horsefly bites in humans
If you’ve been bitten by a horsefly, the area will often become red and raised, and you may experience minor swelling. However, this should go away on its own over a couple of hours or days. That said, it’s not uncommon for horsefly bites to take longer to heal than other insect bites.
In some cases, people can also experience symptoms like…
- A red, raised rash
- Weakness
- Wheezing
- Dizziness
- Puffiness and swelling
Horsefly bites may be painful, but they usually aren’t dangerous to humans – though, in very rare cases, horseflies can pass on a bacterial infection called tularemia (also known as rabbit fever). However, this is considered less of a problem as ticks and Lyme disease, for example.
Some people can experience an allergic reaction to a horsefly bite or develop an infection. This can cause symptoms, such as…
- Swelling or the tongue or throat
- Swollen face, hands, or feet away from the site of the bite
- Dizziness
- Nausea, vomiting, or diarroheoa
Note: If you experience more severe symptoms after being bitten by a horsefly, it’s important to seek medical attention immediately.
Symptoms of horsefly bites in animals
Horsefly bites in animals look similar to those in humans. Horses and cows are a horsefly’s main target, but they’ll bite any large mammal they can detect. Horseflies typically target the neck, underside, legs, or withers; and, if bitten, animals will often develop a red, burning lump.
It’s rare for animals to experience complications from horsefly bites. However, if the bite doesn’t heal as expected or becomes infected, it may leave them vulnerable to more serious infections.
If severe swelling occurs or the animal is intensely itching the bite area, it’s important to contact your vet. In horses, this could be a sign of sweet itch, which is caused by an allergic reaction to fly salvia. There’s currently no known cure for sweet itch, but there are things you can do to manage symptoms. The British Horse Society has more information on sweet itch.
How are horsefly bites treated?
Treating horsefly bites in humans
Treating a horsefly bite is similar to treating other types of insect bites. If you’re bitten by a horsefly, experts generally advise that you…
- Clean the area immediately with soap and warm water using cotton wool or a clean cloth
- Place an ice pack or cold compress wrapped in cloth to help reduce swelling and ease pain
- Apply an antiseptic spray to help to reduce irritation and itchiness
- Take an oral antihistamine to reduce itchiness
Horsefly bites will usually heal on their own. However, if a bite worsens or you experience signs of an infection, such as pus coming from the bite, it’s important to speak to your GP.
As much as possible, experts advise avoiding scratching the bite. Not only will scratching make the bite itchier, but it can also increase the risk of infection.
Treating horsefly bites in animals
If an animal has been bitten by a horsefly, experts advise applying an ice pack or bathing the area with cool, salt water. For multiple bites, applying a mild animal-specific shampoo can help to remove bacteria and relieve inflammation.
Applying an anti-itch remedy, such as colloidal oatmeal, zinc oxide cream, or calamine lotion can also help to prevent animals from rubbing the affected area and making the bite worse.
It’s rare for bites to become infected. However, if the area is open and weeping, bathing it with a mild antiseptic solution can help. If it doesn’t improve, it’s important to speak to your vet.
How can I reduce the risk of horsefly bites?
Horseflies are most active on warm, humid days and are attracted to sweat, carbon dioxide, and dark, quick-moving objects. They don’t like darkness.
With this in mind, there are some steps you can take to reduce yours and your pet’s risk of being bitten.
Tips for protecting yourself from horsefly bites
- Keep skin covered as much as possible
- Wear light-coloured clothing
- Avoid perfumed products
- Where possible, stay away from water in the summer, where horseflies breed
- Apply insect repellent before going outdoors – preferably one that contains 50% DEET
Tips for protecting animals from horsefly bites
- Apply animal-friendly fly repellent
- Keep animals in stables when possible (particularly during the day when horseflies are most active)
- Hang fly tape or fly traps around buildings where animals live, such as stables or barns
- Buy a light-coloured fly rug, fly mask, fly fringe, or other protective gear for your horse
Read this guide to preventing horsefly bites in livestock from Brite and this guide to protecting your horse from horseflies from Vetsend for more information.
Final thoughts…
As the weather warms up, pests like wasps, ticks, and horseflies start to appear. While rarely dangerous, horsefly bites can be painful, so it’s best to do what you can to deter them and reduce your risk of being bitten.
For further reading, head over to the general health section of our website. Here, you’ll find more spring and summer health content, including ways to protect yourself from the sun and tips for staying cool in a heatwave.
Have you been bitten by a horsefly before? What are your top tips for avoiding them? We’d be interested to hear from you in the comments below.
