Cats and Plants

Cats and plants are an interesting combination. Cats need to eat other animals to stay healthy—they do not need to eat their veggies! Some plants can even be bad for cats if they eat or lick them. Lilies, for example, can kill a cat because something in these plants stops cats’ kidneys from working. However, plants are also fun to play with or hide in, and many cats like to eat grass.

Interestingly, there is a special plant that appears to make cats happy. The name of this plant is catnip (Figure 1A). When cats smell catnip, they start rubbing their head against it, they roll around and appear as happy as they could possibly be (Figure 1B). This only happens when cats smell catnip, not when they lick or eat it. Sometimes cats who smell catnip also become playful. Unfortunately, some people compare a cat’s response to catnip to the effect that some drugs have on humans. It is important to mention that catnip is not addictive or unhealthy for cats. When cats are enjoying catnip, they are not “tripping” or “getting high”. The opposite seems to be true: catnip can help cats, especially cats who are kept inside the house all the time. Giving cats catnip every now and then will make their lives more interesting and exciting—which helps cats stay healthy. Catnip can also help big cats in zoos feel less bored. Yes, not only house cats respond to catnip—big cats such as bobcats and lions do as well!

We still do not know why cats respond to catnip the way they do. We also do not know why the “catnip response” is only seen in cats, and not in any other animals.

Why Did We Study Cats and Plants?

Years ago, we adopted cats from a shelter and we wanted to make them really happy. We bought catnip for them, but, to our surprise, none of the cats liked the smell of this plant. They looked at the catnip, but nothing happened. Our cats not responding to catnip was the reason we started to do research on the “catnip response”. How many cats are there who do not like catnip? More importantly, are there other plants that those cats would like instead? We decided to test this, with the help of 100 cats in an animal shelter. We selected several plants we had heard might have an effect similar to catnip. Two of these plants are silver vine (a kiwi plant) and Tatarian honeysuckle (Figure 2A). No one had ever studied the effects of these plants on cats. There was only anecdotal evidence, which is often unreliable.

Which Other Plants Do Cats Love?

Similar to results reported by other scientists more than 50 years ago [1, 2], we found that about 30% of the 100 cats we studied did not care for catnip [3]. When we offered the silver vine and Tatarian honeysuckle plants to the 32 cats who did not like catnip, we noticed that many of them (81%) did love at least one of those plants (Figure 2B). Silver vine was the most popular plant, even more popular than catnip! About 80% of all the cats loved silver vine—smelling this plant made them really happy. Silver vine was also the plant most loved by the cats who did not like catnip. When we gave silver vine to bobcats, they absolutely loved it, too. In addition to silver vine, the cats also loved Tatarian honeysuckle (see this video). Since this happy, playful behavior was first seen after cats smelled catnip, we call the response to all these cat-attracting plants the “catnip response.”

How Do Cats Respond To These Other Plants?

We then wanted to know if the way cats behave after they smell silver vine and Tatarian honeysuckle is the same as the way they respond to catnip. We found that the behavior in response to the various cat-attracting plants was very similar. The way a cat behaved after smelling silver vine, for example, was the same way that same cat behaved after smelling catnip. However, we found that the behavior between cats differed a lot. For example, cat Fluffy would only sit and rub her head on the plant, whereas cat Mittens would become very playful: biting the plant, bunny kicking it, and rolling on her back every now and then. We also saw that the skin on the back of some cats sometimes rippled, or moved in waves, when they smelled these special plants. This was a response that had never been described before.

Which Chemical Compounds Cause The “Catnip Response”?

Plants contain hundreds of chemical compounds. We tested which plant chemical compounds the cats were attracted to. We found that cats not only respond to a compound called nepetalactone, the known cat-attracting compound in catnip, but also to nine other chemical compounds! Most of these compounds looked like nepetalactone, but actinidine and dihydroactinidiolide had a different shape (Figure 3).

Surprisingly, scientists still do not really know how the sense of smell works. We do not know where and how most odorants bind in the nose, and we also do not know how the shape of these smelly compounds determines what they smell like. One super exciting thing that we learned was that only few cats respond to actinidine, but those cats who do like actinidine, love it more than any of the other compounds. This is the first clue that there may be not just one, but multiple olfactory receptors in the nose these cat-attracting compounds bind to!

Discovering that cats love the smell of dihydroactinidiolide was extremely exciting too—and here is why. All other chemical compounds that cats like are, as far as we know, only made by plants or insects. Insects produce these compounds to warn other insects in the group when there is danger. Plants make the same compounds to protect themselves against bugs. Insects that might want to eat the plants smell these compounds and think there is danger, so they avoid eating the plant. Pretty amazing, right? But it turns out that dihydroactinidiolide is also produced by a mammal. This cat-attracting compound was found in the fur of the tail, close to the butt, and in the urine of the red fox. We believe foxes may use dihydroactinidiolide to communicate with each other via smell. Learning that foxes make a compound that cats love made us wonder if cats maybe respond to all these compounds because they already produce some of these compounds themselves. Perhaps cats also use tiny amounts of these compounds to communicate with other cats, and the joyful response only happens when they smell the compounds in large amounts in plants.

How Is Silver Vine Different From Catnip?

We learned that cats who do not enjoy catnip may love other plants such as Tatarian honeysuckle (especially the wood) and silver vine. We now also know which chemical compounds in these plants are responsible for the “catnip response”. We then quantified all the cat-attracting compounds in catnip, silver vine, and Tatarian honeysuckle. This helped us understand how much of each cat-attracting compound is made by these plants. As we expected, nepetalactone was only found in catnip. Interestingly, we also found that several cat-attracting compounds in silver vine were not present in catnip, and that silver vine contained a lot more actinidine than catnip. This may explain why many of the cats who do not like catnip, love silver vine.

Mysterious Cat-Attracting Compounds in Tatarian Honeysuckle

Finally, there was a bit of a puzzle in our research. We let five cats smell catnip for a long time. After 10 days, they got bored with it. We expected that cats who were bored with catnip would also be bored with other plants that contained the same (or fewer) cat-attracting molecules as catnip. However, when cats were bored with catnip and we gave them Tatarian honeysuckle, one of the cats became extremely happy—even happier than when he smelled catnip for the first time. We do not know why this happened, because all the cat-attracting compounds that we found in Tatarian honeysuckle are also found in catnip—sometimes in even higher amounts. This could mean that Tatarian honeysuckle contains other chemical compounds that some cats love, which have not been identified yet. This may explain why some cats who do not like catnip love Tatarian honeysuckle.

As you see, we still do not understand exactly why plants make cats happy and how the compounds that we found in catnip and other plants make cats behave the way they do. We are continuing our research to find the answers to these questions. We also hope that more people will start using catnip, silver vine and Tatarian honeysuckle to help their cats live happier and healthier lives.

Glossary

“Catnip Response”: ↑ Behavior shown by cats in response to smelling cat-attracting plants such as catnip. The behavior typically includes head or cheek rubbing and rolling around.

Anecdotal Evidence: ↑ Something only seen and described by other people, not tested by scientists. It is not always true.

Nepetalactone: ↑ The chemical compound in catnip that makes cats love this plant.

Actinidine: ↑ A cat-attracting compound found in many of the plants that cats love.

Dihydroactinidiolide: ↑ A compound loved by cats that is made by plants and insects, but also by the red fox.

Odorant: ↑ Invisible compounds in the air that can be smelled when they enter the nose. Odorants bind to olfactory receptors.

Olfactory Receptors: ↑ Proteins in the nose that send a message to the brain when an odorant is bound to it. When the messages arrive in the brain, you smell the odorants.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank Joanne Wegiel for the photograph of the Tatarian honeysuckle wooden stems, Marcy Leigh for the photograph of cat Frankie enjoying catnip, and Elizabeth Sellers for the photograph of the Tatarian honeysuckle berries.