How to Treat a Horsefly Bite | Step-by-Step Guide

If you’ve ever been bitten by a horsefly, you’ll know it’s nothing like a mosquito bite. The pain is sharp, immediate, and impossible to ignore — and if you spend your summers around horses, you’ll meet a lot of them. UK horsefly season runs from late May through September, peaks in July, and the cleg flies of the Scottish Highlands need no introduction to anyone who has hacked up a glen. Knowing how to treat a horsefly bite quickly — on you, your friend, or your horse — makes a real difference to how fast you recover and whether the wound stays clean.

What Is a Horsefly?

A horsefly is a large, sturdy flying insect that belongs to the Tabanidae family. There are around 4,450 species worldwide, with around 30 found in the British Isles. The UK has two main culprits: the bigger Tabanus species (the true horseflies) and the smaller, hardier Haematopota pluvialis — the notorious “cleg” or notch-horned cleg fly that is so common in Scotland and northern England. In South Africa, Tabanus species are a common summer nuisance near farms, rivers, and coastal areas in the Western Cape, KZN and the Highveld bushveld.

Horseflies are bigger than your average housefly — ranging from about 6 to 20 millimetres in length. They have large compound eyes, thick bodies, and blade-like mouthparts. Some species have distinctive purple or green bands across their eyes. Clegs are smaller, mottled grey, and creep up so silently that you typically only notice them when the bite has already happened.

Why Do Horseflies Bite?

Only female horseflies bite. They need a protein-rich blood meal to develop their fertilised eggs. Male horseflies feed exclusively on flower nectar and pollen and won’t bother you at all. Females, on the other hand, are persistent hunters. They track prey by size, colour, and movement — and they follow the trail of carbon dioxide that animals and humans breathe out. This is why they seem to zero in on you when you’re exercising outdoors, hacking out at a brisk canter, or mucking out a stable in 25°C heat.

When Are Horseflies Most Active?

Horseflies are most active during warm, sunny daylight hours — particularly in summer. They thrive in humid environments and breed near water. If you live near a farm, river, pond, or coastal wetland, your risk of being bitten is higher. In the UK you’re most likely to encounter them between mid-June and mid-September, with peak activity in July; in South Africa the season runs roughly October to March.

Why Horsefly Bites Hurt So Much

Most insect bites are painful for a moment and then fade. Horsefly bites are different, and there’s a good reason for that.

Instead of simply piercing the skin like a mosquito does, a horsefly uses its serrated, scissor-like mouthparts — called mandibles — to cut through the skin. Think of it less like a needle prick and more like a small slash. The fly then uses tiny hooks along its mouthparts to anchor itself while it feeds, and it releases an anticoagulant to stop your blood from clotting as it drinks.

Mosquitoes inject a mild anaesthetic when they bite, which is why you often don’t notice a mosquito bite until afterwards. Horseflies release no such anaesthetic, so the full pain hits immediately. The Natural History Museum in London notes that this is also why horsefly bites are more likely to become infected — the wound is bigger, messier, and contaminated with the fly’s saliva and any bacteria it has picked up on the way.

What Does a Horsefly Bite Look Like?

A horsefly bite can look similar to other insect bites, which makes it tricky to identify straight away. Typically, you’ll notice a raised, red, tender lump — known clinically as a weal — at the site. The redness and swelling can spread outward from the initial bite, sometimes quite a distance from where the fly actually landed.

In some cases, you may also see a small bruise forming around the wound. On darker skin tones, the area may deepen in colour rather than appear bright red.

Horsefly Bite Symptoms

The most common symptoms of a horsefly bite include a sharp, burning pain, itchiness, redness and swelling around the bite, and sometimes bruising. These symptoms typically ease within a few hours to a few days. If they persist or worsen beyond seven days, it’s worth getting checked out by your GP or pharmacist.

How to Treat a Horsefly Bite at Home

The good news is that most horsefly bites can be managed at home with basic first aid. Here’s what to do straight after a bite. The NHS, NHS inform Scotland and the British Red Cross all back broadly the same five-step protocol.

Step 1: Clean the Wound

As soon as possible, wash the bite site thoroughly with mild soap and plain warm water. Use a clean cloth or cotton wool. This removes bacteria from the surface of the skin and reduces the risk of infection. The horsefly’s mouthparts create a small cut rather than a tidy puncture, which means bacteria can get in more easily — so cleaning is important. If you’re at a yard, an iodine-based wound cleaner from the human first-aid kit (not your horse’s hibiscrub) will do the job.

Step 2: Apply a Cold Compress

Wrap an ice pack or a bag of frozen peas in a cloth and hold it against the bite for about 10 minutes. This eases the pain and helps reduce swelling. Do not apply ice directly to bare skin, as this can cause an ice burn. The cold compress also slows local histamine release, which is why it dulls the itch as well as the pain.

Step 3: Elevate the Affected Area

If the bite is on your hand, foot, or lower leg, try to keep the area raised. For example, if you’ve been bitten on the ankle, lie down and prop your foot up on a cushion. Elevation helps to reduce swelling and can ease the throbbing sensation.

Step 4: Take Over-the-Counter Medication

Over-the-counter antihistamines such as cetirizine or loratadine help relieve itching and reduce swelling. For pain relief, paracetamol is a safe option for most people. Anti-inflammatory medication such as ibuprofen can also help, though it’s worth checking with your doctor or pharmacist first if you have asthma or other conditions that may make ibuprofen unsuitable for you. A 1% hydrocortisone cream from a UK pharmacy can also be applied sparingly to ease itch.

Step 5: Resist the Urge to Scratch

Scratching the bite will almost certainly make things worse. It breaks the skin further, introduces more bacteria, and can turn a manageable bite into an infected wound. If a child has been bitten, make sure their fingernails are clean and trimmed to reduce the damage if they scratch in their sleep.

What About Home Remedies?

You may have heard that vinegar or bicarbonate of soda can help with insect bites. For horsefly bites specifically, these are unlikely to make a meaningful difference. Stick to the steps above for the most reliable relief.

How Long Does a Horsefly Bite Take to Heal?

With proper care, a horsefly bite should settle within about seven days. The initial sharp pain usually fades within a few hours, while the swelling and itchiness may linger for a couple of days. Because horseflies cut through the skin rather than simply puncture it, horsefly bites can take longer to heal than mosquito or ant bites.

If your bite is still painful, growing more swollen, or showing no sign of improvement after a week, see a GP or pharmacist. The NHS Pharmacy First service in England and the Pharmacy First Plus service in Scotland mean that a community pharmacist can now prescribe a course of antibiotics for an infected insect bite without you needing a GP appointment.

Signs of Infection to Watch For

Because a horsefly bite creates a small wound in the skin, infection is a real possibility — especially if you scratch it. Keep a close eye on the bite in the days following the incident.

Signs that the bite may be infected include increasing redness or warmth around the wound, swelling that is getting worse rather than better, pus or discharge from the bite site, a foul smell coming from the wound, red streaks spreading away from the bite (a sign of cellulitis), and fever or swollen glands nearby.

If you notice any of these signs, see a doctor or pharmacist as soon as you can. They may prescribe a course of antibiotics to clear the infection. Flucloxacillin is the usual first-line UK choice for cellulitis from an insect bite, or clarithromycin if you have a penicillin allergy.

When Is a Horsefly Bite Dangerous?

For the vast majority of people, a horsefly bite is painful but not dangerous. That said, there are two situations that require urgent medical attention.

Severe Allergic Reaction (Anaphylaxis)

Some people have a severe allergic reaction to horsefly bites. This is called anaphylaxis and it is a medical emergency. Symptoms develop quickly and may include swelling of the throat, lips, face, hands, or feet, difficulty breathing or swallowing, wheezing, a rapidly increasing heart rate, dizziness, nausea or vomiting, and loss of consciousness.

If you or someone nearby shows any of these symptoms after a horsefly bite, call 999 (UK) or 10177 (South Africa) immediately. Do not wait to see if the symptoms improve on their own. If you carry an EpiPen, use it.

Tularemia and Lyme

In rare cases, horseflies can transmit a bacterial infection called tularemia, also known as rabbit fever. It is uncommon in the UK but more frequent in mainland Europe and can be life-threatening if left untreated. Symptoms include fever, skin ulcers, swollen lymph nodes, and general illness. Although ticks are the main UK vector for Lyme disease, horseflies have occasionally been implicated. If you develop unexplained symptoms in the days following a horsefly bite, speak to a doctor and mention the bite.

How to Prevent Horsefly Bites

Prevention is always better than treatment. Here are practical steps to reduce your chances of being bitten.

Wear the Right Clothing

Horseflies are attracted to large, dark-coloured objects. Wearing light-coloured clothing — a white or cream polo shirt, for example — makes you less of a target. Cover your arms and legs when you’re in high-risk areas, and wear closed shoes rather than sandals. Bear in mind that horseflies can bite through thin fabric, so loose, thicker clothing offers better protection. Riding breeches and full-length jodhpurs are actively useful here.

Use Insect Repellent

Apply an insect repellent before going outdoors. Products containing DEET are the most effective — look for a concentration of around 50% for the best results. Apply it to exposed skin and, if needed, treat your clothing with a permethrin-based product, which provides an additional barrier. Note that permethrin should never be applied directly to skin. UK favourites include Smidge, Jungle Formula Maximum, and Pyramid Repel for hikers and walkers.

Avoid Attracting Them

Skip the perfume or scented body products when you’re heading out into areas known for horseflies. Strong scents attract them. Also avoid strenuous outdoor exercise in hotspots during peak activity hours, since horseflies are drawn to the carbon dioxide you exhale more heavily when working hard.

Know Where to Be Careful

UK hotspots for horsefly activity include working farms and equestrian properties, river banks, ponds, marshes, beach dunes, and any warm, humid, grassy areas in summer. The west coast of Scotland, the Lake District, mid-Wales and the New Forest are notorious. In South Africa, the Lowveld, KZN coastal belt and parts of the Western Cape are similar. If you’re hiking, swimming, or picnicking near these locations, take extra precautions.

Horsefly Bites on Horses: The UK Rider Guide

Horseflies are not just an inconvenience to riders — they are a genuine welfare problem for horses. A swarm of clegs on a summer evening can take a calm horse and turn it into a stamping, head-tossing wreck inside ten minutes. The Bit & Bridle community sees this every July, so this section is specifically for horse owners.

Spotting a Horsefly Bite on a Horse

Horsefly bites on horses typically appear as raised, soft welts — about 1 to 3 cm across — most often on the chest, belly, flanks, neck and legs. Look for a small spot of dried blood at the centre and fresh weals appearing while you watch. Horses respond to bites by stamping, kicking the belly with a hind leg, swishing their tails violently, and rolling more than usual. A horse that has been heavily bitten can lose half a stone of condition in a single hot week from stress alone.

Treating a Horsefly Bite on a Horse

For an uncomplicated horsefly bite on a horse, clean the area gently with hibiscrub or a similar chlorhexidine wash diluted to the bottle’s recommended ratio, then dry with a clean towel. A thin layer of zinc and castor oil cream or a soothing aloe-based product such as Hibiscrub Restore can help reduce itching. Most bites settle within 24–48 hours.

Call your vet if the swelling spreads, the wound starts to drain pus, you see streaks of cellulitis tracking up a limb, your horse is reluctant to put weight on a bitten leg, or your horse shows signs of allergic reaction such as widespread hives, facial swelling or trouble breathing. Severe allergic reaction is rare but is a true equine emergency.

UK Horsefly Protection for Horses

Layered protection works far better than any single product. Effective measures include:

• Fly rugs and full-face fly masks — Bucas Buzz-Off, Rambo Plus, Premier Equine Buster Sweet-Itch combo and Horseware Amigo Bug Buster are the UK best-sellers.
• Spot-on permethrin and cypermethrin pour-ons — Switch (Bayer) and Deosect are the most-used yard products. Reapply weekly during peak season and never to broken skin.
• Spray repellents — NAF Off Citronella, Lincoln Gold Fly Repel Gel, Carr Day & Martin Flygard Extra, Pro-Equine Killer Spray and Equip Citronella all have a decent UK following. DEET-based human sprays should not be used on horses.
• Yard management — empty water troughs of standing rainwater weekly, muck out twice daily, mow long grass round the field shelter, and consider Tabanid traps such as the H-Trap or NZI trap if your yard backs onto woodland or marsh.

Equine Infectious Anaemia (EIA, Swamp Fever)

Horseflies are the main mechanical vector for Equine Infectious Anaemia, also known as swamp fever. This illness can cause recurrent fever, anaemia, oedema and weight loss in affected horses, and some carriers show no symptoms at all but can still spread the disease through subsequent fly bites. EIA is a notifiable disease in the UK under the Infectious Diseases of Horses Order 1987 — by law, any suspicion of EIA must be reported to APHA. Although confirmed UK cases are rare, every horse moved from outside the EU now requires a Coggins test before import. If you own horses and intend to compete abroad or buy imports, talk to your vet about EIA risk during horsefly season.

When to See a Doctor

To recap, you should seek medical attention if the bite has not healed within seven days, if there are signs of infection such as pus, increasing redness, or fever, if you feel dizzy or unwell after being bitten, or if there is any swelling of the face, throat, or lips. Anaphylaxis is a medical emergency — call 999 immediately if you suspect it.

For most people, knowing how to treat a horsefly bite at home is all you’ll ever need. Clean the wound, cool it down, keep it elevated, take appropriate medication, and leave it alone. For related summer-yard advice, see our guides on hay fever in horses, sweet itch and ticks and the broader category of horse care. With a little patience and care, you’ll be back to full comfort within a week — and so will your horse.

Frequently Asked Questions