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Dr. Chrysoula I. Liakou MD, PhD
- Treated online: Yes. A doctor can assess a horsefly bite on camera and treat swelling, itching and infection.
- What they are like: horsefly bites are large and painful and may bleed, and they often become infected.
- First aid: wash the bite with soap and water, hold a cold pack on it for at least 20 minutes, raise the area, and do not scratch.
- Usual course: swelling can grow over several hours and settle over a few days; itching and redness can last up to 10 days.
- Emergency: call 112 for swelling of the lips, mouth or throat, difficulty breathing, or feeling faint after a bite.
Do not book a video appointment if, after a bite, you have swelling of the lips, mouth, throat or tongue, fast or difficult breathing, a tight throat, pale or blue-grey skin, or you feel faint or confused. These are signs of a severe allergic reaction: call 112.
Can an online doctor treat a horsefly bite?
Yes. A horsefly bite is recognised from how it looks and how it happened, and both work by video. The doctor looks at the bite and the swelling around it on camera, checks for infection and for signs of an allergic reaction, and advises on pain relief and care of the wound. If the bite is infected, the doctor can prescribe antibiotics.
How an online consultation helps with a horsefly bite
- The bite seen on camera: The doctor looks at the wound, how far the swelling and redness spread, and how they have changed.
- Reaction or infection?: Swelling that spreads fast in the first hours is usually a strong reaction to the bite, while infection builds over days, and each needs a different treatment.
- Relief that suits you: Painkillers, an antihistamine or a steroid cream, chosen after the doctor checks your other medicines.
- Warning signs explained: Which changes over the next days mean the bite needs another look, and which mean urgent care.
What the doctor checks in an online horsefly bite consultation
The consultation follows a fixed order, and the signs of an allergic reaction come first. The doctor asks about:
- Allergic reaction: swelling of the lips, mouth or throat, breathing difficulty, dizziness, or a widespread itchy rash.
- The bite: where it is, when it happened, how large the swelling is, and whether it is still growing.
- Infection: pus, increasing pain, warmth or redness spreading over the following days, and a high temperature or swollen glands.
- Past reactions: how you reacted to bites and stings before.
- Your health: diabetes, a weakened immune system, and the medicines you take.
Before the call, mark the edge of the redness with a pen and note the time, so the doctor can see whether it is spreading.
What does a horsefly bite look like?
Horsefly bites are large and painful, and they may bleed. You may notice:
- sharp pain at the moment of the bite, and a bite that may bleed
- a raised, itchy lump with redness around it; the redness can be harder to see on brown or black skin
- swelling around the bite that can grow over several hours, sometimes many centimetres across
- itching and redness that can last up to 10 days
Horsefly bites often become infected, so keep the bite clean and watch it over the next few days.
Why do horsefly bites hurt and swell so much?
Because horseflies cut the skin rather than pierce it. Only female horseflies bite: they need a meal of blood to develop their eggs, while the males feed on nectar. A female uses a pair of serrated mouthparts to saw into the skin until small blood vessels break, then feeds on the blood that flows.
- No numbing: unlike mosquitoes, horseflies release no mild anaesthetic, so you feel the bite at once.
- Bleeding: their saliva contains an anticoagulant that stops the blood clotting while they feed, which is why a bite may bleed.
- Swelling: the raised, red lump is the skin’s reaction to the bite, and in some people it grows for several hours.
- Blisters: a stronger reaction can cause fluid-filled blisters, which can become infected.
Scratching lets infection in, and horsefly bites often become infected, so cleaning the bite and leaving it alone matter more than with most insect bites.
When and where do horseflies bite?
Horseflies bite outdoors in the summer months, and they are more active during heatwaves. The UK alone has 30 species, and there are more than 4,500 worldwide. One of the most common in the UK, the notch-horned cleg, is about 1 cm long, dark grey with mottled wings and striped eyes, and flies from May to September.
- Where: near water, in damp woodland and long grass, on heaths, wetlands and farmland, and wherever cattle and horses graze.
- How they hunt: females wait in shady spots, find their prey by sight and fly silently, so you often notice one only when it bites.
- What draws them: large mammals, usually cattle and horses but also people. There is evidence that they home in on the carbon dioxide people breathe out, so anyone exercising outdoors may be at greater risk.
- Dark colours: in a field study in Hungary, a dark brown human-sized model attracted 10 times more horseflies than the same model painted with white stripes, and a light beige model attracted far fewer than the dark one.
A summer with many bites may simply mean more people outside in warm weather with bare skin, rather than more horseflies.
Horsefly bite or another insect?
If you did not see what bit you, the look of the bite helps. Each insect leaves a typical mark:
Swipe sideways to compare →
| Insect | What the bite or sting usually looks like | Read more |
|---|---|---|
| Horsefly | A large, painful bite that may bleed, often with a lot of swelling | This page |
| Mosquito | Small, raised, itchy bumps, often several on uncovered skin | Mosquito bites |
| Midge | Small, raised, itchy bumps, usually in groups | Midge bites |
| Bee or wasp | A painful sting with a small mark where it went in; a bee may leave its sting in the skin | Bee stings Wasp stings |
| Tick | A small, spider-like creature attached to the skin; a spreading round or oval rash later can mean Lyme disease | Tick bites |
| Bed bug | Itchy bumps in a line or cluster on skin exposed in bed | Bed bug bites |
Normal reaction, allergy or infection?
Most of the swelling after a horsefly bite is a reaction to the bite itself. These patterns help tell the three apart:
Swipe sideways to compare →
| Type | What you notice | What to do |
|---|---|---|
| Normal reaction | Pain, a red lump and some swelling around the bite | Cold pack, painkillers and an antihistamine |
| Large local reaction | Swelling many centimetres across, sometimes up a whole limb, growing over hours and settling over a few days | An antihistamine; see a doctor if the swelling is more than about 10 cm across |
| Infection | Redness, warmth and tenderness that spread over days, pus, or a high temperature | See a doctor: antibiotics may be needed |
| Severe allergic reaction | Swelling of the face or throat, breathing difficulty, a widespread itchy rash, feeling faint | Call 112 |
Redness and swelling that start and spread quickly, within hours, are more likely a reaction than an infection. Infection usually builds up over a few days.
Can horseflies pass on Lyme disease?
There is no credible scientific evidence that flies, horseflies included, spread Lyme disease. It is spread by infected ticks. A red rash spreading out from a bite in the weeks after time in woodland or long grass points to a tick bite and possible Lyme disease, and needs a doctor.
How to treat a horsefly bite
Most horsefly bites can be treated at home:
- Wash the bite with soap and water.
- Hold an ice pack or a cold, damp cloth on it for at least 20 minutes to reduce the swelling.
- Raise the bitten arm or leg, if you can, to ease the swelling.
- Take paracetamol or ibuprofen for the pain.
- Ask a pharmacist about an antihistamine for the itch and swelling, and about hydrocortisone cream for itching.
- Do not scratch, and avoid home remedies such as bicarbonate of soda.
If the bite is bleeding, press on it with a clean cloth and cover it with a clean dressing.
How to avoid horsefly bites
No method is complete, because horseflies can sometimes bite through clothing, but these steps lower the risk:
- Wear loose-fitting clothes with long sleeves and long trousers outdoors in summer.
- Choose light colours rather than dark ones.
- Use an insect repellent on exposed skin, as for other biting insects, and put it on after sunscreen.
- Take extra care on hot days near water, in damp woodland and around cattle and horses.
Which horsefly bite treatment might the doctor recommend?
Treatment depends on the size of the reaction and whether the bite is infected. This is the framework the doctors use, in line with NHS guidance.
Swipe sideways to compare →
| What you have | Likely first step | Suitable for online care? | When in-person care is needed |
|---|---|---|---|
| A painful, itchy bite | Cold pack, painkillers and an antihistamine | Yes | Not usually needed |
| Swelling more than about 10 cm across | An antihistamine, and sometimes a short course of steroid tablets | Yes | If swelling affects your breathing or swallowing: call 112 |
| Spreading redness, warmth, pus or a fever | Antibiotics for an infected bite | Yes | If you feel very unwell or the redness spreads fast |
| A bite on the face, near the eye or in the mouth | Assessment of the swelling | Yes, to assess | If it affects your eyesight, breathing or swallowing |
| Signs of a severe allergic reaction | Emergency treatment | No | Call 112 now |
Is your bite infected or just swollen? A doctor can tell you in one consultation.
See available times →Treatment options for horsefly bites
What you can do yourself
- Clean the bite, cool it and raise it, as above.
- Take an antihistamine as soon as you can after the bite, and continue it until the swelling eases, which may take a few days.
- Use hydrocortisone cream for itching, if a pharmacist advises it.
- Keep the bite clean and covered if it is open, and check it each day for signs of infection.
Prescription treatment
A prescription is never issued without a consultation. Most horsefly bites settle with self-care. For a very large or severe local reaction, the doctor may prescribe a short course of steroid tablets, or a stronger steroid cream for the itch. If the bite is infected, the doctor can prescribe antibiotics. If the doctor prescribes, use the prescription at a pharmacy near you.
What does not help
Scratching breaks the skin and lets infection in. Home remedies such as bicarbonate of soda are not recommended. Antibiotics do not help swelling that is a reaction to the bite rather than an infection.
Special situations
Swelling that keeps growing
A large local reaction can grow for several hours and spread up a whole limb, then settle over a few days. Redness that keeps spreading after the first day, with warmth, pain or pus, needs a doctor.
Bites near the eye or in the mouth
Swelling near the eye or in the mouth needs a prompt assessment. Swelling in the mouth or throat that affects breathing or swallowing needs 112.
A previous severe reaction
If you have had a severe reaction to an insect bite or sting before, get medical advice after any new bite, and carry the emergency medicine you have been prescribed.
Walking and cycling in summer
Exercise outdoors may draw more horseflies, so cover up and use a repellent. Other summer health problems are covered on the travel illnesses page.
Diabetes and a weakened immune system
Skin infections can become serious more quickly. Keep the bite clean, and see a doctor at the first sign of infection.
Children
Mobi Doctor consultations are for adults aged 18 and over. A child who is unwell needs a paediatrician or a local doctor in person, and emergency signs in a child mean 112.
When a horsefly bite is treated online, and when you need in-person care
Treated online: horsefly bites with pain, itching or swelling, large local reactions, and infected bites.
In-person care: a severe allergic reaction, swelling that affects breathing, swallowing or eyesight, and an infection with a high temperature in someone who is very unwell.
When to get in-person care
Call 112 or go to an emergency department now for:
- swelling of the lips, mouth, throat or tongue
- fast or difficult breathing, a tight throat or trouble swallowing
- sudden confusion, drowsiness, dizziness or fainting
- red, hot, swollen skin with a very high temperature, shivering or a fast heartbeat
Get medical advice the same day for:
- redness, warmth or pain spreading from the bite
- pus or fluid coming from the bite
- a high temperature with swollen glands
- a bite in the mouth or near the eye
How Mobi Doctor works
- Book a time that suits you: daily 7am–11pm CEST. You can see a doctor over video, usually within 15 minutes. No subscription, and the exact price is shown before you pay.
- Speak to a licensed doctor about the bite: show it on camera in good light, and say when it happened and how the swelling has changed since.
- Leave with a plan: what to do, what to take and for how long, and which signs mean you should be seen in person. If the doctor prescribes, use the prescription at a pharmacy near you.
No sign-up needed
Not sure it’s a horsefly bite? Tick every symptom you have to see each condition page that mentions it. It finds the right page, not a diagnosis: a doctor gives you that on a video call.
Tap the body — an area or a point — to browse symptoms anywhere
Similar symptoms, different condition? Mosquito bites can start the same way. Compare them, or look up any other symptom in the full symptom checker.
Frequently asked questions about horsefly bites
What does a horsefly bite look like?
A horsefly bite is a large, painful, raised lump that may bleed, with redness and swelling around it. The swelling can grow over several hours, and the bite can stay itchy for up to 10 days.
How long does a horsefly bite take to heal?
Most bites settle within a few days. The swelling usually goes down over a few days, while itching and redness can last up to 10 days. See a doctor if the bite is getting worse rather than better.
How do you treat a horsefly bite at home?
Wash the horsefly bite with soap and water, hold an ice pack or a cold cloth on it for at least 20 minutes, and raise the area if you can. Painkillers ease the pain, and an antihistamine or hydrocortisone cream from a pharmacy helps the itch.
Is it normal for a horsefly bite to swell a lot?
Swelling around a bite is common, and some people have a large local reaction: swelling many centimetres across, sometimes up a whole limb, that grows over several hours and settles over a few days. See a doctor if the swelling is more than about 10 cm across.
How do I know if a horsefly bite is infected?
An infected bite becomes hot, red, more painful or more swollen over the following days, and pus or fluid may come from it. A high temperature or swollen glands can follow. Infected bites need a doctor and may need antibiotics.
Why do horsefly bites hurt so much?
Female horseflies cut into the skin with serrated mouthparts and feed on the blood that flows, and unlike mosquitoes they release no numbing substance. Their saliva also stops the blood clotting, so the bite may bleed.
Are horsefly bites dangerous?
Usually not. Most cause pain, swelling and itching that settle within days. The rare dangers are an infection that spreads into the skin around the bite, which needs antibiotics, and a severe allergic reaction, anaphylaxis, which is life-threatening: swelling of the lips, mouth or throat, difficulty breathing or feeling faint after a bite needs 112.
Can horse flies carry Lyme disease?
There is no credible scientific evidence that horseflies or other flies spread Lyme disease. It is spread by infected ticks, so a spreading red rash after time in woodland or long grass needs a doctor.
What attracts horse flies to people?
Horseflies hunt large mammals by sight, and there is evidence they follow the carbon dioxide people breathe out, so exercise outdoors may raise the risk. Dark colours attract more horseflies than light ones, and they are most active on hot summer days.
Should I take an antihistamine for a horsefly bite?
An antihistamine can ease the itching and swelling. Take it as soon as you can after the bite and continue until the swelling eases. A pharmacist can suggest one that suits you.
When should I see a doctor about a horsefly bite?
See a doctor if the swelling is more than about 10 cm across, the bite is getting worse rather than better, there are signs of infection, the bite is in your mouth or near your eye, or you have had a severe reaction to a bite or sting before.
Can an online doctor treat a horsefly bite?
Yes. A doctor can look at the bite on camera, tell a strong reaction from an infection, and recommend treatment. If the bite is infected, the doctor can prescribe antibiotics after the consultation.
- Insect bites and stings, NHS, National Health Service (UK), reviewed 1 June 2023.
- Insect bites and stings, Patient.info, reviewed by UK GPs, updated 14 January 2025.
- Cellulitis, NHS, National Health Service (UK), reviewed 18 April 2024.
- Anaphylaxis, NHS, National Health Service (UK), reviewed 21 June 2023.
- Are horsefly bites on the rise?, Natural History Museum, London, July 2018.
- Notch-horned cleg-fly (horse fly), The Wildlife Trusts, accessed 15 October 2026.
- How Lyme disease spreads, CDC, US Centers for Disease Control and Prevention, reviewed 24 September 2024.
- Striped bodypainting protects against horseflies, Horváth G et al., Royal Society Open Science, 2019.
- Insect and tick bite avoidance, TravelHealthPro, National Travel Health Network and Centre (NaTHNaC), updated 13 August 2026.
This page is for information only and is not a substitute for a medical consultation. Guideline links are provided for transparency; treatment decisions are made with your doctor.
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