Biting Flies in the UK

While many flies in the UK are simply annoying, a few species are capable of biting humans. These bites can cause itching, swelling and discomfort, and in some cases may lead to allergic reactions or secondary infections if scratched. Most biting flies are more active during warmer months and near water, livestock or shaded woodland. Here’s a guide to the most common biting flies in the UK, including what they look like, where they live, and how their bites affect people.

Horseflies (Tabanidae)

Horsefly (Tabanus bromius)
Photo: Erik Karits

Horseflies are among the largest and most persistent biting flies in the UK. Females have strong, scissor-like mouthparts that slice through skin to feed on blood, while males feed only on nectar. They are often dark-coloured with large eyes and can grow up to 2.5 cm long. Horseflies are typically found near livestock, wetlands, or woodlands, especially on warm days. Their bites are painful, can cause swelling and irritation, and may lead to infections if not cleaned properly.

Blackflies (Simuliidae)

Blackfly (Simuliidae) biting

These tiny, dark flies are found near rivers and streams, where their larvae develop in fast-flowing water. Despite their size – just a few millimetres long – blackflies can bite exposed skin and cause red, itchy welts. They tend to bite in large numbers and are most active during summer months. Their bites may go unnoticed at first but become increasingly irritating over time.

Midges (Ceratopogonidae and Chironomidae)

Cloud of midges

Biting midges, particularly those in the Culicoides genus, are widespread in Scotland and northern parts of the UK. They are small (1–3 mm), hard to see, and most active in the early morning and evening. Swarms of midges can make outdoor activities uncomfortable, and their bites can cause itching, redness and swelling. They are especially common in damp, still areas such as bogs, lochs and forests.

Stable Flies (Stomoxys calcitrans)

Stable Fly (Stomoxys calcitrans)
Photo: USDA

Sometimes called biting house flies, stable flies resemble the common housefly but feed on blood. They are often found near farms, stables, and kennels. Their bites are sharp and can be quite painful, leaving red marks and swelling. Stable flies are active in warmer weather and can also affect pets and livestock.

Deer Flies (Chrysops spp.)

Deerfly (Chrysops caecutiens)
Photo: Erik Karits

Less common but still present in some rural areas, deer flies are smaller than horseflies but have similarly painful bites. They are usually brown or yellow with patterned wings and bright eyes. Deer flies prefer wooded and marshy areas and are more likely to be encountered in summer. Like horseflies, only females bite.

Snipe Flies (Rhagio spp.)

Snipe fly (Rhagio scolopaceus)
Photo: Lars M.

Snipe flies are medium-sized with long legs and a tapered abdomen. Some species, such as Rhagio scolopaceus, will bite humans if disturbed. These flies are usually found in woodlands and meadows and are more common in late spring and early summer. Their bites are uncommon but can cause a sharp sting and mild irritation.

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