Summer Sore Savvy

What Exactly is a Summer Sore?

A summer sore is a moist wound caused by large mouth stomach worms called Habronema.

The adult worms produce eggs that are shed in the horse’s manure and quickly hatch. The tiny larvae that emerge have to get back into a horse to complete their life cycle. Maggots ingest the worm larvae as they feed, and the worm larvae develop inside the maggots as the maggots develop into adult flies.

Flies are drawn to moist areas around the horse’s mouth, eyes, urethra, and wounds. When they land to feed at these places, the larvae sense the moisture and bail out.

Most larvae find themselves near the mouth, are swallowed by the horse and mature into adult worms in the stomach. When the larvae are deposited into an area of skin an open wound called a Summer Sore develops. Larvae can also be deposited inside the lower eyelid causing a large irritated swelling in the lid.

Summer sores are raw and painful and attract more flies causing a vicious cycle and making them difficult to resolve.

My Horse Has One – Now What??

Treatment for Summer sores is comprised of a dewormer to kill the parasite and a topical solution to soothe and allow the inflamed area to heal. See our recommendations for deworming here.

The sooner treatment is started, the better! Sometimes in advanced cases the larvae have to be dug out and removed before healing can occur. Any small sore that occurs in moist areas of the body during fly season should be treated immediately. On the mouth the sore is usually at the corner. At first the sore may be mostly inside the mouth and a small bulge on the corner is all that is visible. If you see flies congregating at your horse’s mouth it only takes a moment to check if something is developing while it is still easy to treat.

How Can I Keep My Horse From Getting Them?

Prevention of Summer Sores is achieved by managing the flies! Here are a few tips for keeping the flies managed in your barn areas.

  • Remove manure and food waste at least once a day (ideally twice). Do not pile it near your horses and best practice is to remove it to a trash bin and have it hauled away.
  • Use of Fly Masks that prevent the flies from those areas on the face. You can also use fly sheets with belly bands to help protect other areas of the body.
  • Keeping sheaths cleaned and the use of SWAT if flies are seen near the sheath. Particularly in older geldings or ones with loose hanging sheaths.
  • Use of Fly strips/Natural insecticides
  • If you use fly traps place them away from the barn and feeding areas. Instead put them near where you put manure.


Call your veterinarian for a definitive diagnosis or if a sore is not resolving. If your horse has a Summer Sore that needs treated, Contact Us! Dr. Debra has a custom blended salve that is safe and effective!!