Ectoparasites in horses


There are several ‘types’ of fly, which can prove a torment to horses during spring and summer months. Biting flies can pierce the horse’s skin and feed on its blood while nuisance flies lay secretions in and around the horse’s eyes, mouth, nose and other sensitive areas. Aside from the threat of an allergic reaction and the annoyance, flies can carry diseases, which they can spread from horse to horse.

A very common type of fly is the Horsefly (approximately 8-10mm), which typically comes out in June and July, especially around woodlands. They tend to bite the horse’s underside, legs, neck and withers and can cause painful lumps. Horse flies will also bite humans. Black flies are another common pest and are small in size (approximately 2-5mm). These breed in rapidly moving water and are most noticeable at dawn and dusk. These flies commonly feed around the face—particularly inside the ears. This is where they trigger allergic skin reactions to their saliva, and distract the horse—but also on the horse’s neck and underside.

Midges and Sweet-itch

Sweet-itch is a common skin disease that affects many horses and ponies in the UK and at present there is no cure. Once a horse develops the allergy it will generally be for life. Therefore it is the responsibility of every horse owner to be vigilant in order to aid early detection, and to take preventative measures to prevent unnecessary suffering.

The condition is caused by a reaction to the saliva of biting midges during the months of April to early November. It causes horses to rub their manes, tails and sometimes their undersides too. In the United Kingdom, it is the antigens present in the saliva of the Culicoides midge and to a lesser extent, a member of the black fly family called Simulium Equinum that horses are allergic to. The severity of the condition varies from horse to horse; some will only rub occasionally, while others will rub themselves bald, causing open sores.

Treatment revolves around anti- inflammatory therapy which is often unsatisfactory and can have serious side effects if used long term. Preventative measures are therefore crucial to avoid the condition and limit the suffering which can arise from the intense and unrelenting itching.


Lice are wingless, species specific, flattened insects, usually 2–4 mm long. The claws of the legs are adapted for clinging to and moving among hairs. Lice thrive where they can keep warm and are often found at the roots of the forelock and mane but they can be found anywhere on the body particularly if the coat is thick.

The symptoms of a lice infestation include:

  • A dull, listless coat
  • Patchy hair loss
  • Matting of body hairs, mane and tail
  • Itching and rubbing against posts and stable walls
  • Biting at the skin
  • Loss of condition in more severe cases
  • In more severe case, anaemia due to ongoing blood loss
  • Visibility of lice and eggs on the surface of the skin and in the coat.

Lice are readily passed from one horse to another by physical contact, and can also be spread by the sharing of brushes and equipment from one horse to the next. Sharing equipment is not recommended as nits (louse eggs) can live for a few days on equipment away from the horse, transferring to the next horse when the equipment comes in to contact with it.