Catnip’s insect-repelling powers grow as Puss chews on it

Damaging the leaves boosts the plant’s chemical defenses — and their appeal to cats

This cat is seen nibbling on catnip. This plant is known to bug insects. A new study finds that this plant releases more pest-repelling compounds as a cat chews, licks or mashes it.

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For many cats, a mere whiff of catnip can send them into a licking, rolling, plant-shredding frenzy. That destruction boosts the plant’s natural defenses against insects and birds, new data show. And there’s a bonus: It also ups the plant’s appeal to cats.

Compared with intact catnip leaves, crushed ones emit more compounds into the air. Called iridoids, these oily chemicals repel pests. They also seem to encourage cats to continue rolling around in the remains of the mashed leaves. This will effectively coat cats in a type of all-natural bug spray.

Masao Miyazaki works at Iwate University in Morioka, Japan. This biologist was part of an international team that analyzed catnip (Nepeta cataria) and silver vine (Actinidia polygama). That second species is a plant common in Asia. It brings cats much the same sense of the joy, excitement and well-being that catnip does. Both plants naturally produce iridoids. Those plant-defense chemicals tend make the leaves taste bad to pests.

With six border collies at home, Miyazaki considers himself more of a dog person. Still, he finds cats interesting — because they’re the only animals known to use catnip and silver vine in this way.

As cats toy with silver vine, the damaged leaves release lots of iridoids. In fact, Miyazaki’s team finds, those leaves emitted about 10 times more of these compounds than did undamaged leaves. Damaging the leaves also changed the relative amounts of different chemicals these leaves spewed into the air. Crushed catnip leaves released even more of its insect repellents — some 20 times more. Most of this plant’s emissions were an iridoid known as nepetalactone (Ne-peh-tuh-LAC-tone).

As part of their new study, Miyazaki’s team made synthetic iridoid cocktails. Their recipes mimicked those of chemicals emitted by damaged catnip and silver-vine leaves. These lab-made mixes chased off more mosquitoes than did chemicals found in undamaged leaves.

The researchers also presented cats with two dishes. One had intact silver-vine leaves. The other contained damaged leaves. Without fail, cats went for the bowl of damaged leaves. They licked and played with it, rolling against the dish.

This suggests that when a pet plays with its leaves, both the plant and Puss will get an insect-repelling benefit. In fact, Miyazaki’s group notes that in a study with silver vine, last year, they showed that rubbing and rolling on the leaves “can protect cats from mosquito bites.”

Anil Oza is the summer 2022 science writing intern at Science News. He graduated from Cornell University with a degree in neurobiology and science communication.

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