Warm weather and longer days mean summer is finally here – and so are the flies. Emma Farrell MRCVS and NAF highlight the signs and symptoms of fly irritation and how best to control it.
From biting horse flies and midges to distracting gnats, flies can pose a real problem to our horses and ponies, both when ridden and when grazing. Problem flies fall into three categories:
Biting species, e.g. horse fly, stable fly and midges
Nuisance species, e.g. house flies
Parasitic species, e.g. bot fly
Many flies also act as vectors for disease, such as summer sores, sarcoids and bacterial infection.
Symptoms of fly irritation in horses
Every horse reacts differently to flies – some aren’t bothered while others will do everything to avoid them, and some have a nasty reaction to bites. Look out for:
Behavioural changes – tail swishing, ear flicking, mane/head shaking, kicking at the flanks, biting at the skin and a general increase in agitation.
Fly bites – raised, inflamed and sometimes ulcerated lumps which are often associated with heat, pain, swelling and intense itchiness, which then leads to self-trauma.
Problem areas – flies commonly congregate around the eyes where they can pass on bacterial and parasitic infections and lead to excessive tear production/staining and irritation. Due to their irritation, horses rub at the eyes, which can lead to ulceration of the eye surface. This painful complication may lead to the eye being held closed or an increase in blink rate.
Self-trauma – in cases of Sweet Itch, self-trauma occurs due to the irritation associated with fly bites and subsequent allergic reactions. The resulting broken skin has hair loss and scabs, and is sore and oozes clear/bloody fluid, which then unfortunately attracts further flies.
Habronemiasis – multiple, small, firm ulcerated skin lumps are seen with the parasitic condition habronemiasis (summer sores) and are most often observed on the legs, belly, around the eyes, folds of skin and at the site of pre-existing wounds.
How to treat fly irritation in horses
Superficial wounds and bites which are not associated with any signs of infection (heat, pain, swelling, discharge, malodour) can usually be managed by bathing in an appropriate antiseptic solution and the application of a soothing ointment to the area.
Barrier creams may also be useful in preventing further contamination and reducing further fly bites.
If signs of infection or flystrike are present, if the eyes are involved or if your horse appears otherwise unwell, then it is always best to immediately seek the advice of your vet at an early stage, especially in the summer months when wounds and skin irritations can worsen rapidly.
All fly repellents in the UK are required by law to carry an HSE or BPR registration number, which ensures the product is using one of the recognised fly repellents proven to be both safe and effective. There are only a small number of repellents approved for horses, including DEET (diethyl-m-toluamide) and PMD (p-menthane-diol).
In NAF’s experience, different repellents work better for different horses, so if you find one is not effective try a different one with a different active ingredient.
Stabling in the day and turnout at night reduces the risk of horse fly bites, as can grazing away from the woodland areas that flies favour.
Ensure horses are not turned out near standing water – a field pond can be a real magnet for midges! If possible, turn out in a hilly field, which encourages a constant breeze.
Installing fans within the stable, avoiding grazing at dawn/dusk and selecting for grazing in exposed windy areas will reduce exposure to midges.
Practice good stable and paddock hygiene to remove stable fly breeding sites such as dung and dung heaps, and standing water sources.
Make use of fly traps, fly papers and fly screens in stables and use an ivermectin wormer after the first frost in winter to kill off bot fly larvae overwintering inside your horse.
Using an effective fly repellent spray containing DEET or permethrin/cypermethrin (preferably with an oil base) is essential. Sprays are easy and quick to use, but for horses scared of the spray action, and for harder to reach or more sensitive areas such as the face, gels are a good option.* Use sprays both on your horse and in the stable environment.
Natural fly repellents may also assist and barrier creams/oils can be useful, especially if there are localised areas of skin irritation such as in and around the ears or on the face.
Use barriers such as anti-midge/fly turn-out rugs with neck covers, fringes, veils, masks and nose nets, and turning out with companions allow horses to share the task of deterring flies.”
