Why do dogs eat grass?
It's a common question, but in asking the question, an assumption is revealed.
The assumption is that dogs are not supposed to eat grass.
After all, no one asks why we humans eat chicken, corn on the cob, fish, or strawberries.
The short answer is that dogs eat grass because it tastes good and it provides some nutrition.
It is not a sign of worms, an upset stomach, or any kind of nutritional deficit.
That's the short answer.
Now let's look at the question a bit deeper.
Do wolves, fox, coyotes, and dingoes, also eat vegetable matter?
The answer is "yes."
Wolf biologist David Mech notes that grass appears in 14-43% of all wolf scat found in North America and Eurasia. Plant material in fox and coyote scat, including grass, is so common as to be unremarkable.
Leopards, jaguars, mountain lions, and bobcats also eat surprising amounts of grass. A sample of 215 leopard scats collected in the Tai National Forest of the Ivory Coast, for example, found 17% had a considerable amount of grassy vegetable matter.
Bears too eat a lot of plant material. Though classified as the largest carnivores in the world, bears eat more vegetable matter in their diet than flesh, and grass is a major food source.
So why do "carnivores" so often eat grass?
For the same reason you and I eat most of the foods we eat; it tastes good.
Of course the other answer is that it is maladaptive for them not to do so.
Let's explore that idea a bit more.
Specialization in food sources is a terrific idea so long as the world stays exactly the same, day in and day out, season after season, year in and year out.
But, the world is both temperamental and unreliable.
Crippling winters, blistering summers, and poorly timed rains can decimate populations of prey species.
Disease can wipe out herds, migration routes can change without warming, and new species can invade.
Water holes may dry up, salt licks may disappear, and predators can injure themselves in the chase.
And yet every few days, a predator must eat.
And that's the problem: The chain of life is so easily snapped.
For a meat-eating predator, the weakest link is the absence of ready prey, easily caught, day in and day out, in good health and bad, dry season and wet, winter and summer, year after year.
And so wolves, coyotes, dingoes, bears, lions, bobcats and jaguars have all evolved to eat plants, as well as flesh -- a way of "hedging the bet" for a few days against the vicissitudes of life.
Yes these animals will try to bring down a deer- or rabbit-sized meal if they can. But if they cannot, then they will try to catch a few rats or mice, a lizard or a snake, a frog or a turtle.
And if push comes to shove, there's always grasshoppers, crickets, and verdant grass along the creek. And it does not hurt at all that some of that grass actually tastes pretty good!