Why does my horse have raised lumps where flies have bitten it?

Read time: 3 minutes

Overview

Raised lumps where flies have bitten your horse are often a normal local skin reaction. They can look like small bumps, welts or puffy areas, and they may appear soon after biting insects have been active. In many cases they settle as the irritation eases, but there can be several possible causes, including fly bite sensitivity, mild skin inflammation or a reaction to repeated bites.

Things To Check

1. Check when the lumps appeared, especially whether they show up after turnout, in the evening, or during warmer fly-heavy periods.

2. Look closely at the skin for redness, heat, broken skin, scabs, crusting or any discharge.

3. Note whether the lumps are only in bite-prone areas such as the face, neck, belly, legs or along the mane and tail.

4. See if your horse is rubbing, stamping, tail swishing or seems bothered by touch over the area.

5. Check whether the bumps are small and isolated or spreading into larger patches.

6. Compare both sides of the body to see if the reaction is localised or more widespread.

7. Think about recent changes in turnout, stable time, grooming, washing or insect pressure that might have triggered the reaction.

Common Causes

The most common cause is a local reaction to fly bites. Some horses develop raised, puffy lumps from the saliva or irritation caused by biting insects, and the skin can look quite dramatic even when the issue is limited.

Repeated bites in the same area can also lead to more noticeable swelling and sensitivity. If your horse has been bothered by flies for a while, the skin may react more strongly than you’d expect.

Less commonly, the bumps could be part of a broader insect sensitivity or another skin irritation that happens to show up where flies have been active. If the skin is also sore, very itchy, or not settling, it may need a closer look.

What To Do

Start by checking whether the area is simply puffy or whether there’s broken skin, heat or discharge. Gentle monitoring is useful, especially if the lumps are small and your horse otherwise seems well.

Try to reduce further bite pressure as much as you reasonably can. Keeping an eye on turnout times, stable management and fly activity can help you spot patterns and plan around the worst periods.

If the skin is intact, avoid overhandling the area and keep routine grooming gentle. If your horse is rubbing or stamping, note how often it happens and whether it’s getting worse.

If the reaction doesn’t start to settle, spreads, or your horse becomes increasingly uncomfortable, it’s sensible to speak to your vet for advice.

Products That May Help

For horses that are dealing with fly-season irritation, this collection may be useful as part of a practical daily management routine to help support comfort and grooming care.

Horse Fly Sprays & Summer Care

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