PEOPLE have been sharing shocking pictures of pus-filled horsefly bites, but what are the pests and how can you stay safe.

Here's everything you need to know.

3 Female horseflies have a nasty bite that can cause a dramatic reaction Credit: iStockphoto - Getty

What is a horsefly?

The horsefly is a large, hairy fly whose bite can be extremely painful.

The females will bite animals - including humans - for blood, which they need to produce eggs.

The female flies have two razor sharp cutting blades that pierce the skin.

The pests then use a sponge-like part of their mouths to lap up blood.

Male flies do not bite instead drinking nectar from flowers or fruit.

What do horseflies look like?

Horseflies are much larger than an average fly.

They are dark, hairy flies although they may also have brightly coloured patches.

The pests measure about 1cm to 2.5cm in size.

3 People have been sharing images of the horrific pus-filled blisters caused by horseflies Credit: MEN Media

How do you treat a bite?

A bite from a horsefly can be very painful.

The bites are not generally harmful, although there is a risk of infection and people have been sharing shocking pictures of their reactions.

Bites can take a while to heal and symptoms can include a large rash, dizziness, weakness, wheezing and swelling.

The NHS advises:

Clean the area

Apply a cold compress

Keep the wound covered to prevent infection

Elevate the affected area to reduce swelling

Do not scratch

You should contact your GP or NHS 111 if:

The symptoms do not improve within a few days

You're stung around your mouth, throat or eyes

An area of 10cm or more becomes swollen and red

The wound becomes infected

You have a fever, swollen glands or flu-like symptoms

You should dial 999 if:

You are wheezing or having difficulty breathing

You have a swollen mouth, throat or face

You are nauseous or vomiting

Your heart rate increases

You feel dizzy or faint

You have difficulty swallowing

You lose consciousness

3 A bite from a horsefly can be very painful and the bitten area of skin will usually be red and raised Credit: MEN Media

How can I protect myself?

Some insect repellents will help keep the horseflies at bay and it's a good idea to protect yourself if you're going near grassland, livestock or water.

Light coloured clothing will also make you less of a target for the flies, which are attracted to dark, moving objects.

The flies like hot weather and don't normally head into dark areas - so you will be better protected in the shade.

How common are they in the UK

Horseflies like warm weather and as summers get hotter Brits can expect to see more.

The flies normally appear in June and July.

Horseflies are often found around ponds, pools, woodlands, grass and livestock.