Fly Biting: Is it a Seizure or a Digestive Disorder?

Jennifer Coates, DVM
By Jennifer Coates, DVM on Apr. 4, 2016

When I was in veterinary school, I learned that as long as a dog has normal eyesight, fly biting behavior (snapping at the air as if trying to catch a nonexistent fly) is usually a symptom of a partial seizure.

A partial seizure is caused by abnormal electrical activity within a relatively small portion of the brain. I don’t know what part of the brain needs to be stimulated to make a dog exhibit fly biting behavior but the result was thought to be this specific set of movements. Partial seizures were not the only possible cause of fly biting, but they were the most likely… or so I was taught. New science is casting doubt on this assumption, however.

Researchers at the University of Montreal Veterinary Teaching Hospital evaluated seven dogs (an admittedly small sample size) to “characterize fly biting, perform a complete medical evaluation of dogs presented with fly biting, and evaluate the outcome of this behavior following appropriate treatment of the underlying medical condition.” Let me summarize the paper’s most intriguing results.

All seven dogs were diagnosed with some type of gastrointestinal GI) disease, including delayed gastric emptying, inflammation of various parts of the GI tract, gastro-esophageal reflux, and/or a flaccid and distended stomach. When the dogs received treatment for their GI disease, the fly biting completely resolved in five cases.

One other dog was also diagnosed with a neurologic disorder (Chiari malformation) and responded to a medication used to treat seizures and nerve pain but not to GI treatment. The owners of the seventh dog did not institute the recommended treatment and their dog’s fly biting behavior remained unchanged.

The researchers make the following points in their paper:

The data indicate that fly biting may be caused by an underlying medical disorder, GI disease being the most common. At home, 3 dogs (dogs 1, 2, and 4) consistently presented more fly biting following feeding, suggesting potential postprandial [after eating] discomfort. Dog 1 presented fly biting during hospitalization within 30 min of being fed. The video analysis data showed that in all fly biting dogs, the jaw snapping was preceded by head raising and neck extension. In 2 dogs, head raising and neck extension occurred more frequently than jaw snapping. Dogs 3 and 6 presented repeated raised head and neck extension during the consultation. On home videos as well as consultation and hospitalization videos, all dogs raised their head and extended their neck prior to fly biting.

Head raising and neck extension in the dogs may be similar to Sandifer syndrome, a rare paroxysmal movement disorder in infants characterized by abnormal movements of the head, neck, and trunk in association with gastroesophageal reflux (GER) disease (1214)…. Sandifer movements are often precipitated by meals, unlike other movement disorders (12,14). Other conditions such as delayed gastric emptying when associated with GER disease may also result in abnormal posturing such as seen in Sandifer syndrome (12). It is still unclear why less than 1% of children with GER disease (14) present abnormal movements and others do not (12). It is believed that the abnormal movements are learned behaviors by children to reduce reflux (12) as well as protect air passages from reflux and relieve the abdominal pain caused by acid reflux (16,17).

The take home message? If your dog is fly biting, make sure your veterinarian performs a complete work-up for gastrointestinal disease. Chances are, you’ll find something that responds to treatment.


Prospective medical evaluation of 7 dogs presented with fly biting. Frank D, Bélanger MC, Bécuwe-Bonnet V, Parent J. Can Vet J. 2012 Dec;53(12):1279-84.

Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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