Why do dogs roll in grass? For that matter, why do dogs roll in general? Dog owners around the world have no doubt been both amused and dismayed by their dog's desire to roll around...sometimes it's in clean, green grass, and sometimes it's in something stinky or gross, like a dead slug. A dog's sense of smell is much stronger than ours, and they also like to leave their own scent trace wherever they go. Their desire to roll in grass is likely related to both of those aspects of dog behavior.
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Why do dogs roll?
A BBC story reported that a researcher studied the behavior of wild wolves, coyotes, and foxes in Canada. The researcher, Simon Gadbois from Dalhousie University in Halifax, Nova Scotia, observed wild canines and his own tracker dog rolling in smelly poo. It seems remarkable that the scent wouldn't interfere with the dogs' own ability to track other scents, but it doesn't seem to. The dogs probably use the feces to cover up their own scent.
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A wild dog rolling in a patch of grass that has rabbit feces in it, for instance, means that wild dog can cover its own scent with the scent of its prey, which may help it get closer to the next rabbit it sees.
Why do dogs roll in grass?
According to a 2018 paper published in Frontiers of Veterinary Science, a dog's sense of smell is believed to be 10,000 to 100,000 times as sensitive as our own! Dogs have approximately 300 million olfactory receptors in their nose, compared to people who have only approximately six million. The portion of a dog's brain that is dedicated to interpreting scents is 40 times greater than that of people.
Under perfect conditions, dogs have been reported to have detected objects or people as far as 12.43 miles away. It's fair to say that when a dog rolls in a patch of grass, they are likely smelling something that their dog owners just can't sense. Whether it's a smell that is pleasing to them or one that they think will mask their own scent is hard to say.
Dog rolling behavior
Sometimes, dog rolling behavior is part of play. They may roll around in a patch of grass on a sunny day because the warm grass feels good on their back, or they want to scratch their back where they can't reach, or it may even be because they want to encourage you to scratch their bellies! While grass feels mostly soft to the touch to us, it is actually mildly abrasive, so rolling in grass could help to clean their fur, loosening bits of stuck on dirt or even loose hair. Rolling on their backs in a patch of grass may remove insects that may be hovering around.
Another theory about why dogs roll in grass or any other smell object may be to remove the scents of humans. If your dog is frequently bathed, it may like being clean, but it may not like the unnatural smell of the shampoo — even though the shampoo probably smells good to most dog owners.
When you're on a walk with your dog, you may want to keep moving and get some exercise, but your dog likely wants to investigate something every three feet. This is normal for just about any dog. Because their sense of smell is so strong, they are smelling literally everything that has brushed the grass recently. If another dog or cat came by or there's anything that smells like a crumb of food, they're going to be extremely interested in that.
You may notice that your dog rubs their face in certain areas, or rubs their body on something like a light pole. Dog trainers call this dog rolling behavior scent rolling. It may have been a way for dogs to carry information back to their pack. If a dog brought back a scent of a prey or a predator, then the other dogs would know that the prey or predator was somewhere nearby.
In conclusion
By all accounts, there are a few reasons for a dog rolling in a patch of grass. Rolling in grass probably either feels good to your dog, or else your dog has a good reason for wanting to do it — like it's sense of smell is so strong that it smells something you can't see, and it is trying to cover up its own scent with the other scent.
A dog rolling in grass is not inherently dangerous so you don't necessarily need to stop them from doing it, but it could be a good idea to be mindful of whether pesticides have recently been sprayed on the grass or if pests like ticks might be present. If your dog smells foul after a post-grassy rub, it's likely that it's trying to cover up its own scent. Maybe in your dog's mind, he's still a wild dog on the plains, remembering his own wild dog behavior while on the hunt.