Why do cats like grass and catnip?

All cats, domestic and feral, instinctively graze. While experts have yet to agree on a conclusive reason for this, there do seem to be some benefits to the cat that eats grass.

Nutritionally speaking, grass is mostly fiber and useless to cats. Cats don’t have the digestive enzymes required to process fiber. As a result, grass usually causes the cat to regurgitate. Naturally, many pet owners assume that this is a bad thing and do their best to keep their cats away from grass. There are, however, some very good reasons for cats to eat grass, and some very good reasons to allow this behavior to happen.

For a cat, regurgitation may be the biggest benefit of eating grass. Small animals such as mice and birds are often devoured whole, including fur, feathers, and bones. The cat cannot digest these parts, meaning they either remain in the stomach indefinitely or pass the intestine whole, an uncomfortable and dangerous process. Instead, the cat eats some grass between meals and regurgitates the parts, now wrapped in a tidy little grass bundle.

Even domestic pets will eat grass if available, despite the gentler diet. They can also benefit from eating grass. While grooming, the animal is likely to ingest hair. This hair is indigestible as well, and collects in the stomach. By eating grass, the cat is able to bring up the furball before it becomes to large and causes a painful blockage in the intestine.

Although largely indigestible, cats may receive some nutritional value from grass as well. Fiber cannot be absorbed, but the moisture found in grass can, and with it vitamins A and D, as well as trace levels of some minerals.

Another proposed reason for eating grass has been put forward as well: cats like it. It may be that they simply enjoy the taste.

Whatever the reason, cats will continue to eat grass. In fact, when access to the lawn is denied, cats will often seek out a substitute. They may try to eat houseplants, which, depending on the plant in question, can be harmful or even lethal. They may select other fibrous substances, such as fabric or wire, which can also be exceedingly dangerous. Owners of indoor cats might consider potted grass, which can be found in some florists, garden centers and even some pet shops.

Nepeta cataria, commonly known as catnip, is an herb of the mint family with properties similar to valerian. Contrary to popular belief, catnip is not a drug. Catnip is not addictive and cats cannot overdose. Like valerian, catnip can act to stimulate the cat's nervous system.

The reaction to catnip is hereditary. Some cats respond and others do not. Cats that do like catnip are reacting to a substance called nepetalactone, an essential oil in the catnip leaves. This substance triggers a chemical reaction in the feline brain which causes the cat to act silly. This reaction to nepetalactone is not fully understood but is believed to be hallucinogenic. Typically, the cat will lick, eat or roll in the catnip, and generally go crazy.

Nepetalactone can be released by shredding catnip leaves. Responsive cats are reacting to the smell. By rolling, chewing or licking the catnip, a cat can release more oil, getting a stronger scent and a stronger reaction. Catnip introduced in other forms, such as in a gel cap, will not excite the cat because there is no scent. However, even cats with an impaired sense of smell are still able to enjoy the effects of catnip. While catnip acts as a stimulant when inhaled, ingested catnip tends to have a sedative effect.

Typically, catnip will continue to stimulate responsive cats for between 10 and 30 minutes before the effect wears off. Cats will not respond to continued exposure, but, if removed, the cats will display the same behavior again if the catnip is reintroduced a few hours later. Kittens of less than 2 to 3 months old will not respond to catnip. Continued exposure to catnip will do no harm to a cat, but it will lessen the catnip’s effect.

Catnip can be used for training to reinforce desired behavior. For instance, a cat could be encouraged to use a scratching post by placing leaves or using a catnip spray.

Catnip can also be used as an insect repellant and is effective against mosquitoes and cockroaches. The scent seems to be unpleasant to rodents as well.