Cats chewing catnip boost the plant’s insect repellent powers

For many cats, a single whiff of catnip can send them into a frenzy of licking, rolling, and shredding plants.

This destruction amplifies catnip’s natural defenses against insects and its appeal to cats, according to a new chemical analysis. Compared to intact leaves, crushed leaves emit more volatile compounds called iridoids, which act as an insect repellent, researchers report June 14 in iScience. The higher emissions also seem to encourage cats to continue rolling in the remains of the plant, effectively coating themselves with natural insect repellent (SN: 04/03/21).

Masao Miyazaki, a biologist at Iwate University in Morioka, Japan, and his colleagues analyzed the chemistry of catnip (Nepeta cataria) and the Silver Vine (Actinidia polygamous), a plant common in Asia that has a similar euphoric effect on cats. Both plants naturally produce iridoids, which discourage insects from nibbling the leaves.

When cats played with silver vine, damaged leaves released about 10 times more iridoids than intact leaves, and also changed the proportion of chemicals released. The researchers also found that catnip, when crushed, released more than 20 times more of its insect repellent, primarily a type of iridoid called nepetalactone.

With both plants, lab-made iridoid cocktails that mimic those of damaged catnip and silver vine repelled more mosquitoes than chemical solutions that mirrored those of intact leaves, the study found.

The team also presented the cats with two dishes – one with intact silver vine and one with damaged leaves. Without fail, the cats would go to the damaged leaf container and lick and play with the dish and roll against it.