Clinical Notes : Dermatology

200. Horsefly Bite

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

  • much larger than an average fly (1cm to 2.5cm)

  • dark, hairy, may also  have brightly coloured patches or black and white back

  • generally found near to cattle, horse stables, ponds, pools, woodlands, and grassy areas

  •  more prevalent during hot, sunny weather with low wind, and are more aggressive when thunder accompanies hot weather.

  • does not transmit any disease apart from swamp fever, which can be fatal in horses, mules, donkeys and zebras.

  • insect repellent (DEET) does not prevent horsefly bites

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Male and female


The females​

  • will bite large mammals (humans, dogs, cows, horses) for blood, which they need to produce eggs.

  • anchors to the skin while drinking the blood with the help of small hooks along its mouthparts

  • have two razor sharp cutting blades that pierce the skin, causing a cut rather than a small puncture hole

  • releases substances that stop blood clotting at the point of skin puncture

  • the female fly then use a sponge-like part of their mouths to lap up blood.

  • will not leave behind any mouthpart or stinger when they bite people


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

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Reaction to bite


Humans find horsefly bites painful.

Itch and some swelling is common.


Usually, a weal occurs around the site.

Other symptoms may include ​:

  • dizziness, weakness

  • nausea

  • urticaria, wheezing, angioedema

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General :

  • clean site with mild soap and plain water with clean cloth or cotton wool

  • avoid scratching as this increases chance of infection

  • vinegar and bicarbonate of soda are unlikely to help


Pain :

  • paracetamol and ibuprofen

  • avoid aspirin in under 16 year old

Itch :

  • crotamiton cream or lotion

  • hydrocortisone cream or ointment

  • antihistamine tablets

Swelling :

  • cold compress or ice pack for 10 minutes spells

  • antihistamine tablets

Infection :

  • mark edges of rash with pen to monitor increase in size

  • review red flags for infection and safetynet

  • standard anttibiotics for skin infection / cellulitis

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Insect bites and stings


Updated: Jan. 2020


Horsefly bite treatment: Three ways to soothe the wound recommended by the NHS

Andrews L

Expess, online Feb. 2020


Are horsefliy bites on the rise ?

Natural History Museum

Online February 2020



What to do about a horsefly bite

Medical News Today

Online Feb. 2020



Horsefly bites! What you need to know.

Warson Training Services

Online, Feb. 2020


An insight into the sialome of the horse fly, Tabanus bromius

Ribeiro JMC, Kazimirova M, Takac P,  Andersen JF, Francischetti IMB


Published online 2015 Sep 11


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Horseflies are present countrywide but are a particular nuisance in Co. Kerry and Cork.


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