Summer Sores

House or Stable Flies

Surprisingly, summer sores are caused by a worm that is transmitted to the horse by common flies.New window.

Summer sores are caused by the larvae of stomach worms, the Habronema muscae and Draschia megastoma. When house or stable flies bite the horse, the larvae migrate into the wounds and form hard nodules of raised tissue, causing severe itching. These nodules may ulcerate, weep fluid, and bleed, attracting more flies and worsening the irritation. With a consistent deworming program along with a good fly prevention regime, summer sores can be prevented.

Controlling the causes of summer sores in horses

• Two treatments of Ivermectin each year will control stomach worms and summer sores.
• Larvae in the summer sore lesions and the adult worms in the stomach can be controlled with a deworming paste or liquid, such as Equimax, Equiminth, or Equimec (administered at regular worming intervals of six to eight weeks during the high risk period). Check with your veterinarian as to the best schedule for your horses.

Fly prevention in the horse barn

• Hang fly strips or traps around the stables and barn or install automated misters or insecticide systems to minimize the number of flies around the areas where horses are kept.
• Apply fly sprays or wipe your horse down with special wipes each day to keep flies from landing on horses.
• Fly masks, sheets, and leg wraps are helpful in keeping flies from biting vulnerable areas.
• Consider using biological controls, such as predatory wasps, that feed on fly larvae.

The combination of a regular deworming program, a good fly prevention program, and good stable and yard hygiene will greatly reduce the likelihood that summer sores will make you and your horse miserable.