Fly biting

Lore & Background

Before an episode begins, dogs raise their heads and extend their necks and appear to focus on something in the air. Episodes may occur sporadically or at regular intervals, and consist of a varying number of snaps. These episodes may be accompanied by behavioral changes such as agitation or increased owner attachment, or other behaviors, such as jumping, pica, and licking. Licking is the most common co-occurrence in literature on the syndrome, and includes licking of the front limbs, hips, air, and floor.

Reader's Guide

Fly biting is an uncommon idiopathic syndrome with multiple speculated causes, including epilepsy, compulsive disorder, gastrointestinal conditions, and eye disease. Seizure activity is considered one of the more likely causes, with epileptic discharge in the visual cortex connected to subsequent fly catching. In some cases, antiepileptic drugs successfully reduce or eliminate fly catching. Compulsive disorder is another possible cause, diagnosed when antiepileptic drugs have no effect. Gastrointestinal conditions have been linked to fly biting, with some dogs showing decreased behavior after treatment. Eye disease, specifically synchysis scintillans, was the first published association but lacks substantiating research. Treatment varies widely; for dogs without gastrointestinal issues, fluoxetine has been suggested as an initial trial due to its greater effectiveness compared to phenobarbital. The syndrome remains poorly understood, and dogs may undergo multiple treatments before finding success.

Did You Know?

• Cavalier King Charles Spaniels appear to be predisposed to fly catching syndrome.
• Licking is the most common co-occurring behavior with fly biting.
• One study found an increase in fly biting in some dogs following meals.
• The Canine Epilepsy Project has looked for floaters in the eyes of many fly biting dogs without finding any.

The Episode: What Owners Witness

Fly biting—sometimes called fly catching or fly snapping—describes a puzzling canine behavior in which a dog deliberately and intently snaps at the air, as though attacking invisible insects. Before an episode unfolds, the dog typically raises its head, stretches its neck forward, and locks its gaze on something seemingly present in the empty space before it. The snapping itself can range from a single quick motion to a series of repeated bites, and episodes may strike unpredictably or follow a recognizable rhythm. What makes the syndrome particularly concerning for owners is the constellation of accompanying behaviors. Dogs may become agitated, cling more tightly to their humans, jump, or develop pica, the urge to chew non-food items. Licking stands out as the most frequently reported companion behavior in veterinary literature, with dogs directed at their own front limbs, their hips, the air, or the floor. The age at which a dog first exhibits these episodes varies widely, and while Cavalier King Charles Spaniels appear especially prone, the condition has been documented across a broad spectrum of breeds and mixed-breed dogs.

A Puzzle of Rival Explanations

Because fly biting is classified as an uncommon idiopathic syndrome, no single cause has been confirmed, and veterinary medicine continues to grapple with multiple competing theories. Epileptic activity in the visual cortex is considered one of the stronger candidates; neurologists view the episodes as a form of complex partial seizure that produces abnormal movements while the dog stays conscious. In some cases, antiepileptic medications have successfully reduced or eliminated the snapping, lending weight to this hypothesis. When seizure medications fail to make a dent, clinicians may pivot toward a compulsive disorder diagnosis, a canine analogue of obsessive-compulsive disorder marked by repetitive, purposeless behavior with no identifiable underlying condition. Gastrointestinal distress has also entered the picture: case studies show that treating stomach or intestinal issues can diminish or even halt the episodes, and one study noted a spike in fly biting after meals, hypothesizing that pain drives the head-raising and neck-extension postures. The oldest published explanation tied the behavior to eye floaters from a condition called synchysis scintillans, but the Canine Epilepsy Project has examined the eyes of numerous affected dogs without finding floaters, and later publications largely dismiss eye disease as a cause.

Finding the Right Treatment

Because fly biting can stem from several different conditions, there is no one-size-fits-all protocol, and many dogs cycle through multiple therapeutic approaches before landing on something that works. When a snapping dog also shows signs of gastrointestinal upset, veterinarians recommend a thorough medical work-up; if a digestive condition is identified, treatment might involve dietary adjustments, hypoallergenic food, antacids, or antibiotics, and the fly biting often improves alongside the gut health. For dogs whose work-up clears the gastrointestinal track, pharmacological options shift toward neuropsychiatric medications. Phenobarbital and other antiepileptic drugs have been tried, but research indicates they are generally less effective against fly biting than fluoxetine, an antidepressant. One study specifically proposed starting with a four- to six-week trial of fluoxetine for dogs that show no other seizure history. The practical reality for owners is that treatment is highly individualized: the same syndrome in two different dogs may respond to completely different interventions, and patience through a trial-and-error process is often part of the journey.

Breed Tendencies and the Limits of Knowledge

Although fly biting has been recorded in a wide array of breeds and mixed-breed dogs, Cavalier King Charles Spaniels stand out as a group with a notable predisposition to the syndrome. The condition is described in veterinary literature as uncommon and idiopathic, meaning it arises without a clearly identifiable external trigger, and remains poorly understood even by the professionals who treat it. The age at which a dog first begins snapping at the air is highly variable, ruling out a simple developmental milestone as an explanation. Because the syndrome can be driven by epilepsy, compulsive disorder, gastrointestinal pain, or possibly other yet-unidentified factors, the same outward behavior may represent entirely different internal problems in different animals. This multiplicity of potential origins is what makes fly biting so resistant to a unified clinical framework. The fact that the first published account linked the behavior to a specific eye condition, only for later research to largely refute that connection, illustrates how the field's understanding has evolved incrementally. For owners and veterinarians alike, the syndrome remains a case-by-case challenge, demanding individualized investigation rather than a single diagnostic shortcut.