Biting flies cause significant welfare harm to horses through painful bites, skin irritation, eye disease, and relentless harassment that prevents normal rest and grazing behaviour during summer months.
Fly-related welfare problems are among the most seasonal but significant issues affecting horses in summer. Constant biting fly harassment prevents normal rest and grazing — behaviours that are fundamental to horse welfare — and causes cumulative stress from incessant skin irritation. Horses in heavily infested environments may become so irritated and agitated that normal management becomes difficult and risk of injury from spooking or avoidance behaviour increases. Sweet itch — the intense allergic reaction to Culicoides bites seen in susceptible ponies and horses — causes severe itching, self-trauma through rubbing, and secondary skin damage that can be debilitating. Affected animals may rub themselves raw on fences and posts, causing open wounds that attract further flies and secondary infection. Comprehensive fly management for sweet-itch horses includes fine-mesh whole-body rugs, housing during high-midge-activity periods, application of repellent sprays, and in severe cases medical management with corticosteroids during the affected season. Fly management should be considered a welfare obligation rather than an optional comfort measure.