Need a nudge to keep battling bugs through the summer? Flies aren’t just bothersome to your horses and you. They can also cause sickness or injury. Here’s how.

Spreading disease. Flies transport the viruses and bacteria that lead to influenza, equine infectious anemia, pigeon fever (dryland distemper), salmonella, and vesicular stomatitis—as well as a range of skin disorders.

Causing injuries. Constant shoo-fly stamping can loosen shoes and aggravate impact-related injuries, such as arthritis and ringbone. Seriously bothered horses can hurt themselves in other ways (rough contact, entanglement) as they seek relief from itchy, stinging pests.

Degrading condition. Severe fly infestations can even cause horses to lose weight because of interrupted grazing time and lost sleep.