Why do dogs eat grass?

KohakuMunch, munch on grass during a walk. Why do dogs eat grass?

The answer in 30 seconds

Research says it is not always because they feel sick.

Why dogs eat grass is not clearly understood. People often say dogs eat grass to make themselves vomit when they feel sick, but in a US survey, only a small share of dogs looked ill before eating plants or often vomited afterwards. Researchers think eating grass is a normal dog behavior, possibly inherited from wild ancestors.

A black Bernese Mountain Dog with its face in the grass of a planting bed — A Bernese Mountain Dog eating grass. Eating grass is a common behavior in dogs.Photo: BunbunYU / CC0 (cropped) / Wikimedia Commons

Lots of dogs eat grass

In a paper published in 2008, researchers at the University of California, Davis, reported the results of surveys of dog owners. When 47 owners of healthy dogs visiting an animal hospital were asked, 79% said their dog had eaten grass or other plants. In a further internet survey of owners of plant-eating dogs, 68% of the 1571 answers that met the study's conditions said their dog ate plants daily or weekly, and grass was the plant eaten most often.

Do they eat it because they feel sick?

People often say that dogs eat grass when they feel sick, so they can vomit. But in the same survey, only 9% of dogs often looked ill before eating plants, and only 22% often vomited afterwards. Younger dogs ate plants more often, and they were also less likely to look ill beforehand or vomit afterwards. No clear link was found with the type of food the dogs usually ate. The researchers think eating grass is a normal behavior for dogs.

Figure: Survey results on dogs eating grass

The first bar is from 47 owners; the others are from 1571 survey answers (2008 paper).

A habit from wild ancestors?

Plant material is also found in the droppings and stomachs of wolves and other wild members of the dog family. Dr. Hart, from the research team, thinks eating grass may be a trait inherited from wild ancestors. One idea is that grass passing through the gut made the intestines move more actively, helping to wrap up worms and carry them out of the body. However, this is still not a proven answer. Some vets also say that dogs may eat grass when they are bored or anxious.

KohakuEven wolves eat grass. Perhaps it is a habit passed down from their ancestors.

What to watch out for, and when to see a vet

Even if the grass itself is harmless, owners are advised to watch out for weed killers and insect killers sprayed on lawns. Slugs and snails in the grass can also carry a parasite called lungworm. On walks, keep your dog away from sprayed areas. If your dog keeps eating grass and vomiting over several hours, seems unwell, or wants only grass instead of its usual food, the advice is to see a vet.

Figure: Things to watch out for on walks

Based on advice from the Irish Blue Cross.

Want to know more?

The survey also found that younger dogs were more likely to eat plants other than grass.
Studies of droppings suggest that 11-47% of wild wolves eat grass.
Early findings from the same researchers suggest that cats eat plants less often than dogs.

KohakuEating grass is usually normal behavior. But keep your dog away from sprayed grass, and see a vet if they seem to have an upset stomach.

Quick quiz: test yourself

What share of dogs often vomit after eating grass?

Show the answer

22% In a US survey, 22% of dogs often vomited after eating plants. Eating grass is thought to be normal dog behavior in most cases.

Sources

Characterisation of plant eating in dogsApplied Animal Behaviour Science（査読論文、2008年。カリフォルニア大学デービス校ほか）
Why do dogs and cats eat grass?dvm360（論文の著者 Benjamin Hart 博士の解説）
Why Do Dogs Eat Grass?The Irish Blue Cross（アイルランドの動物福祉団体・動物病院）

This article was written after checking the sources above as of 2026-10-03. Explanations may change as research progresses. Photo credits are shown below each photo.