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What is a horsefly?

If you've spent a lot of time outdoors this summer, you may have spotted the short, sturdy horsefly, a member of the Tabanidae insect family.

Like houseflies, horseflies have large eyes and rather thick bodies, but they are larger in size - ranging from around 6-20 millimetres in length.

It's the female horsefly that's most intimidating, with a jaw shaped like scissor blades, called a mandible, which the fly uses to latch on to large animals and feed on blood. Horseflies are drawn to big, dark-coloured animals like horses, but this doesn't stop them from biting humans during the warm summer daylight hours, when they're most active¹.

What does a horsefly bite look like?

Skin specialist Sreedar Krishna says: "A horsefly bite can look very similar to a mosquito bite, or any other form of insect bite, so it can be difficult to identify the exact offender.

"Typically, a horsefly bite will be a raised, itchy, and tender lump. The pain, redness and swelling can often expand a distance away from the initial bite."

Like other insect bites and stings, a horsefly bite can be painful and irritating. Common symptoms include:

• A sharp, burning sensation.

• Picazón.

• Redness and swelling around the bite.

• Sometimes, bruising around the bite.

The good news is these symptoms should disappear within a few hours or days.

Why are horsefly bites so painful?

On the downside, these typically short-lived symptoms often hurt more than other insect bites: "In contrast to other insects, horseflies bite through the skin using their sharp jaws rather than simply piercing the skin," says Krishna.

"Moreover, mosquitoes release a mild anaesthetic into the skin during bites which numbs the area. Horseflies do not, and so are appreciably more painful."

Aside from disrupting your summer with temporary pain and discomfort, a horsefly bite is generally not something to worry about. In fact, they are much more of a problem for their preferred target - horses - because horseflies can carry a disease that's life threatening to them (equine infectious anaemia, also known as 'swamp fever'²).

Horseflies do not transmit severe diseases to humans, but sometimes being bitten by a horsefly may cause an reacción alérgica³ or lead to an infecciones.

Horsefly bite symptoms of concern

"You should seek medical attention immediately if you feel unwell after a horsefly bite - this can include feeling light-headed or dizzy," warns Krishna.

• Infección - the small puncture wound of a horsefly bite can also increase the risk of infection. Be sure to look out for signs of infection such as pus or a foul smell.

• Anafilaxia - this severe allergic reaction requires urgent medical attention - call for an emergency ambulance (999 in the UK). Signs include worsening pain, wheezing, difficulty breathing, a rash that spreads, and swelling of the lips.

• Apply insect repellent before going outside.

• Wear light-coloured clothing - horseflies are attracted to darker colours.

• Cover up your arms and legs and wear closed-toed shoes.

• Don't wear any perfume - scents attract these flying insects.

• Be wary during strenuous outdoor activities - horseflies love the scent of carbon dioxide, which you exhale in greater amounts during exercise³. Of course, exercise is important, so if you're going to be active ensure you use other protective measures in high-risk areas.

• Know the high-risk horsefly bite areas - frequent hot spots include farms - as horseflies are attracted to horses and cattle - and warm water sources like ponds, streams, and rivers - as many horseflies lay their eggs near water and are most active during hot and humid conditions.

• Avoid walking through long grass with exposed feet, ankles, and legs.

"Remember, in most cases time is a healer, although you will want something to help control the pain and irritation."

Krishna's advice on treating a horsefly bite:

• Effective home remedies include applying an ice pack or a bag of frozen peas to the area. If the horsefly bite is on an area of skin you can elevate (such as your foot or hand), it would be worthwhile keeping it raised - for example, by lying down and propping it up with a cushion - as this will reduce swelling.

• Over-the-counter los antihistamínicos such as cetirizine can help reduce itching and swelling.

• Simple painkillers such as paracetamol, y anti-inflammatory medication such as ibuprofen, can help to reduce pain. You may wish to check with your doctor if you are allowed to take ibuprofen. For example, some people with asthma are advised to avoid anti-inflammatory medication.

• Try your very best not to scratch the bite as this can break the skin and lead to infections.

"Assuming that the skin does not become infected, I would expect a horsefly bite to settle within seven days," advises Krishna. "If it does not, or the pain is worsening, I would recommend seeing your doctor for further guidance."

In most cases, the irritation and pain of horsefly bites are short-lived. Avoid spending the summer months worrying about these critters by following our prevention and treatment tips when you can and enjoying the warm weather!

1. Lucas et al. "Diversity and seasonality of horse flies (Diptera: Tabanidae) in Uruguay".

2. GOV.UK, "Equine infectious anaemia (swamp fever): how to spot and report it".

3. Whyte et al. "Tabanidae insect (horsefly and deerfly) allergy in humans: A review of the literature.