Why do flies bite?

Flies bite mammals to cut through the skin and feed on their blood. Be this horses, humans, cows, or sheep! Flies aren’t picky but they will try to access areas of the horse with thinner skin for easier access to blood vessels. These are commonly the inner upper thighs, necks, and withers.

                                                           Aqueos Horse Shampoo to southe irritated skin

Which flies bite horses?

There are a few main types of flies that bite horses. The main culprit you’ll probably be aware of is the horsefly (Tabinidae) - a large fly with a very painful bite that often leaves a large, sore lump in its wake.

A different fly that plagues horses, and often their riders as well in the summer, is the blackfly (Simuliidae). They are particularly numerous around woodland and waterways, are smaller than horseflies and their bites aren’t as painful, however, they particularly like the ears and the belly of horses, both of which can be very irritating.

In addition, midges are another flying nuisance that will bite your horse. They are tiny but their bite can become very itchy, and you might see horses rubbing away the tops of their tails and manes if they get bitten a lot.

Finally, stable flies will be a common fly found in the yard. They use manure, wet bedding and dirty, moist straw as breeding grounds. They’ll prefer to bite your horse around their legs and bellies and can cause some serious irritation at the bite sites.

What happens when flies bite horses?

When a fly bites a horse, the horse will create an allergic inflammatory reaction at the site of the bite. Normally, the inflammation will resolve after a few days and the swelling will settle down. Sometimes horses will be bitten so much that their immune system goes into overdrive, and they become hyper-sensitised to any further bites. This can cause a much more exaggerated reaction to any further bites.

How to treat a fly bite yourself

Fly bites can become weepy, especially if the horse starts scratching them. This then attracts more flies to the bite and can increase the chance of them becoming infected. It is always best to try and keep the bite clean and to wipe away any serous discharge (clear, yellow-coloured fluid). You can use disinfectant wipes to make sure the bites are clean and dry as much as possible. Ideally, the bites should then be covered by a fly rug to prevent more flies from getting attracted to them.

When do you need to call the vet about a fly bite?

If you notice a fly bite becoming very swollen and the discharge turns from clear fluid to yellow and thick pus, you should think about calling the vet. If horses have been scratching them, this leaves them at risk of becoming more inflamed and exposed to becoming infected, especially as horses will be scratching them on dirty objects such as fence posts, stable walls or trees. Not only that but the more weepy they become, the more likely even more flies will be attracted to the bites and cause infection too.

If the bites become really infected and topical treatment isn’t enough, sometimes you might need to have systemic antibiotics prescribed for your horse, as well as some anti-inflammatories. Your vet will be able to advise the best course of action once they’ve seen the fly bites.

Furthermore, you should also call the vet if your horse is scratching so much that they’re removing their coat and their skin is becoming red and raw. There are medications to try and help relieve the itchiness as well as dampen down the body’s allergic reaction to fly bites if your horse has become hyper-sensitised.

How to prevent fly bites on your horse

Prevention is better than cure as they say, and there are plenty of things you can do to help prevent those flies having a feast. The number one way is to provide a physical barrier to the flies getting at your horse’s skin. Fly rugs are widely available and can include very effective belly covers and fly masks with ear covers. Make sure your horse’s fly rug is snug enough to prevent flies from sneaking through gaps and getting in between the rug and your horse’s skin.

The next thing to do is arm yourself with some strong fly repellent. Although it is said that dietary supplements like garlic can help deter flies. Nothing comes close to DEET or permethrin-containing fly spray. It can be easy to miss key areas of your horse’s body if they dislike you spraying in between their back legs or around their ears, but you can get around these problems by spraying the repellent onto a sponge or cloth and wiping those areas gently instead.

Finally, avoid areas and times of day when you know flies are going to be more numerous. For example, avoid hacking in woodland or turning out your horse near trees. In addition, dawn and dusk will be fly and midge peak times, so plan your turnout and riding schedules to avoid these times if your horse is particularly sensitive or bothered by them. 

This article was written by Alice Barker BVSc MRCVS