Why are flies suddenly much worse after rain?

Read time: 3 minutes

Overview

It often happens because rain changes the local fly environment, not because anything is necessarily wrong with your horse. Wet weather can create damp, sheltered spots where flies and midges breed or gather, and rain can also bring a burst of warmth and humidity afterwards, which often makes biting insects feel much more active.

Sometimes the issue is also more noticeable because rain washes away dust and changes where your horse is standing, so they end up in a spot with more shelter, standing water or still air. A few simple checks can help you work out whether it’s mainly an environment problem or whether your horse is reacting more than usual.

Things To Check

1. Check whether the flies are worse in certain places, such as near hedges, muck heaps, gateways, water troughs or damp field edges.

2. Look for standing water, boggy patches, dirty drains, wet bedding or other damp areas that may be attracting insects.

3. Notice whether the problem is strongest after rain stops, at dawn or dusk, or on warm still days, as timing can point to midge activity.

4. Check your horse’s face, belly, ears, legs, tail head and any fine-skinned areas for rubbing, stamping, twitching, sores or signs of irritation.

5. Look at rugs, masks and fly sheets to make sure they fit well and aren’t trapping heat or rubbing damp skin.

6. Consider whether your horse has been sweating more, since moisture, warmth and body odour can make them seem more attractive to flies.

7. Check stable doors, vents and field shelter entrances for poor airflow, because still air can make biting insects more noticeable.

Common Causes

The most common reason is that rain creates the damp, warm conditions flies and midges tend to like. After wet weather, they may breed more quickly or gather around wet ground, manure, and sheltered spots.

Another common cause is simple concentration. If your horse is standing in a smaller, drier, more sheltered area after rain, the insects around that spot can seem suddenly worse even if overall numbers haven’t changed much.

Warm, humid weather after rain can also make midges and flies feel more active. Horses with thick coats, sweaty skin, or areas already irritated by biting insects may seem extra bothered at these times.

Less commonly, a horse that is rubbing, stamping or head shaking more than usual may be reacting to bites, skin irritation or a different discomfort that makes the fly problem look worse than it really is.

What To Do

Start by reducing the conditions flies like most. Keep muck removal regular, empty or manage standing water where you can, and avoid leaving wet feed, bedding or dirty buckets sitting around.

If possible, turn out in the breeziest area available and use shelter or movement to your advantage. A light breeze can make a big difference, and changing turnout times may help if flies are worst at dawn or dusk.

Check your horse daily for rubbing, damp patches, scabs or sore skin so you can spot a pattern early. If a rug, mask or sheet is getting wet and staying damp, take time to dry it and make sure it still fits comfortably.

For horses that are clearly struggling with flies after rain, a calm, consistent fly-season routine can help support day-to-day management. That usually means keeping the environment as clean and dry as practical, watching for triggers, and adjusting turnout or shelter use when conditions change.

Products That May Help

For horses that seem more bothered by flies and midges after wet weather, a fly-season routine can be easier to manage with the right basics to hand.

Horse Fly Sprays & Summer Care

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