Biting Insects
Biting Insects, Inflammation, and Why Most Strategies Are Reactive
Every horse owner has walked into a paddock and seen it.
Raised welts.
Hot, swollen patches.
Belly lines chewed raw.
Ears flicking.
Tail swishing constantly.
Sometimes the swellings are the size of a third of a hen’s egg. Not small irritations, but significant inflammatory reactions.
Most management strategies are reactive. Spray the horse after the insects arrive. Apply ointment after the skin erupts. Rug the horse once the damage is visible.
The horse has already mounted an inflammatory response by that point.
What Is Actually Happening
Biting insects such as midges, mosquitoes, and flies inject saliva when they feed. That saliva contains proteins that trigger a local immune response.
In sensitive horses, the reaction can be disproportionate. Mast cells release histamine. Local blood vessels dilate. Fluid accumulates. The result is a raised, firm, sometimes hot swelling.
In some individuals, this progresses to:
Intense pruritus
Skin thickening
Hair loss
Secondary bacterial irritation
Behavioural agitation
This is not simply a skin issue. It is an immune response.
Why Fly Sheets Only Partially Work
Fly sheets reduce insect landing pressure. They can be helpful, especially in high-midge environments.
However:
They often leave the belly exposed.
They do not protect the legs completely.
They do not prevent insects from targeting the face and ears.
They do nothing to alter the inflammatory response once bitten.
They are mechanical barriers, not immune modulators.
The Inflammatory Threshold
Some horses swell dramatically. Others barely react.
That difference is rarely random.
It reflects:
Immune sensitivity
Inflammatory load
Skin barrier integrity
Nutritional status
Oxidative balance
When a horse’s systemic inflammatory load is high, the threshold for reaction lowers. Minor insults produce exaggerated responses.
When systemic balance is stronger, reactions tend to be smaller and shorter-lived.
Calendula, The Marigold Approach
Calendula, derived from marigold, has long been used topically for skin support.
Its traditional applications include:
Soothing irritated tissue
Supporting epithelial repair
Modulating mild inflammatory responses
Assisting superficial wound healing
When applied early to insect bites, a calendula solution may help calm the local reaction and support faster skin recovery. It works after contact by influencing the inflammatory environment in the tissue.
Owners often report that welts reduce faster and irritation appears less intense when applied promptly.
The key is early intervention, not waiting until the skin is heavily inflamed.
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Practical Field Experience, Application Matters
Over the years, I have trialled many topical strategies for managing horses during peak insect pressure. Most approaches are reactive. Spray after the welts appear. Treat after irritation sets in.
One product that consistently stood out in my own management program was a marigold-based coat spray used daily during high insect seasons.
I do not use it as a conventional spray. Many horses dislike aerosol or pump application, especially around the belly line and flanks.
Instead, I use a pipe rail painting mitt, the type available from hardware stores. I apply the solution to the mitt and hand wipe the horse thoroughly, including belly, inner thighs, and lower flanks.
The difference in skin comfort and visible swelling response was significant in my own horses.
Why this method works better than spraying:
• Full surface contact
• Better belly coverage
• Reduced startle response
• Thicker, more even application
• Direct observation of skin condition during application
It becomes both a treatment and an inspection process.
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Why It May Help Without Being a “Repellent”
Marigold, calendula, and similar botanical extracts are traditionally used to support:
• Skin barrier integrity
• Local inflammatory balance
• Surface hydration
• Epithelial recovery
If the skin barrier is stronger and local inflammation is moderated early, the visible reaction to insect activity can appear dramatically reduced.
That is different from claiming insect eradication.
The insects may still land.
The tissue response may simply be calmer.
For many horses, that distinction matters more than the label.
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The Bigger Lesson
Mechanical barriers help.
Environmental management helps.
Topical support helps.
But early application, proper coverage, and reducing tissue reactivity can change the entire visual outcome.
Owners often chase the insect.
Sometimes the smarter strategy is to strengthen the skin.
Environmental Management Still Matters
Topical support should not replace management.
Standing water control reduces mosquito breeding.
Dung management reduces fly populations.
Shelter positioning influences midge exposure at dusk.
Timing turnout can reduce peak insect pressure.
Insect pressure is seasonal and geographic. Protocol must match the environment.
The Bigger Picture
Repeated insect attack is not just cosmetic.
Chronic irritation increases stress.
Constant agitation reduces rest quality.
Skin trauma increases infection risk.
Energy expenditure increases with constant movement and swishing.
If reactions are severe, it may be worth evaluating overall inflammatory status, forage quality, and antioxidant intake.
The immune system does not operate in isolation from nutrition.
Practical Takeaway
Mechanical protection helps.
Environmental control helps.
Topical support helps.
But the most resilient horses are those with stable metabolic and immune systems.
Insect pressure is external. The response is internal.
The goal is not simply to chase flies. It is to reduce the size of the reaction when contact occurs.