What causes fly bites to swell up on horses? | arlo.® Atlas

Read time: 3 minutes

Overview

Fly bites can swell up on horses because the skin reacts to the bite itself, the horse may be sensitive to insect saliva, or the area may have been irritated by scratching, rubbing or repeated biting. Most swelling is local and settles with time, but it’s worth checking the horse carefully so you can spot anything that needs a vet.

Things To Check

1. Check when the swelling first appeared and whether it gets worse after turnout, grooming, exercise or being stabled.

2. Look closely at the area for redness, heat, broken skin, scabs, discharge or a central bite mark.

3. Feel whether the swelling is soft, firm, painful or spreading beyond the original bite.

4. Notice whether the horse is itching, stamping, tail swishing, rubbing or nibbling at the area.

5. Check if there are multiple swollen spots, which can point to repeated bites rather than one isolated one.

6. Look at the horse’s general behaviour and appetite so you know whether this is just a local skin reaction or something more widespread.

7. Consider whether the horse has had this sort of reaction before, especially during warm weather or heavy fly season.

Common Causes

The most common reason is a normal local skin reaction to the bite. Some horses simply swell more than others, especially around thinner skin such as the belly, legs, face or ears.

Another common cause is sensitivity to fly saliva or midge bites. These horses can develop larger, itchier lumps than you might expect from a small bite.

Swelling can also come from rubbing, scratching or stamping after the bite happens. That extra irritation can make a small bite look much bigger.

If the skin has been broken, the area can become more inflamed and may look more swollen than a simple bite reaction. Less commonly, a bite can be followed by a mild skin infection.

In some horses, repeated bites in one area cause several small swellings that merge together, especially during peak fly season.

What To Do

Start by keeping a simple record of when the swelling appears, where it is and whether it changes over a day or two. A photo can help you compare it later.

Keep the area clean and dry if the skin is broken, and avoid making the horse more uncomfortable by over-rubbing or picking at scabs.

Try to reduce further irritation by managing flies around turnout and stable time, and by checking for patterns such as certain paddocks, times of day or weather conditions that seem to make it worse.

If the horse is very itchy, keep a close eye on whether the swelling is linked with ongoing rubbing or stamping, because that can make the problem bigger even when the original bite is small.

If the swelling is mild and the horse is otherwise well, monitoring for a short period is often sensible. If it keeps returning, is getting worse, or doesn’t seem to settle, ask your vet for advice.

Products That May Help

During fly season, a few owner-friendly essentials can make day-to-day management easier and help you stay on top of irritation, cleaning and routine care.

Horse Fly Sprays & Summer Care

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