We now know why cats chew grass on cats

Les herbes aux chats – especially for cats (Nepeta cataria) and the silver vine (Actinidia polygama) – are known to lead cats to euphoric behavior. Prof. Masao Miyazaki’s team at Iwate University (Japan) has been interested in their effects for several years. Elle now explains in a new study published on June 14, 2022 in the journal iSciencewhy domestic cats often chew these herbs.

Repellent molecules hidden in the leaves of grasses in cats

In the face of insects, plants develop defense mechanisms. A repulsive effect that mammals – including humans – have been able to exploit by applying, for example, leaves on the body. A previous study published in early 2021 by Masao Miyazaki, Reiko Uenoyama and their colleagues, found that cat weeds can have a repellent effect on mosquitoes through particular molecules produced by the leaves, called iridoids. Catarrh produces an iridoid called nepetalactone when silver vines produce a more complex mixture of nepetalactol, dihydronepetalactone, isodihydronepetalactone, iridomirmecin, and isoiridomircin.

Domestic cats (Felis silvestris catus) show an unusual but characteristic response to catarrh (Nepeta cataria) and with silver vine leaves (Actinidia polygama) care consists of licking and chewing the plants, rubbing the face and head against the plants and rolling on the plants“Japanese biologists recall in their new study. It is by rubbing on plants that they transfer iridoids to their fur to protect themselves from stings. But why do they chew them?

Increased molecule release

The hypothesis of a true consumption of the plants was quickly swept away. “Although léchage and chewing of plants favor their ingestion and digestion in most animals, preliminary studies have shown that the discussions did not have a minimum, there is no plant material.“They found that by damaging the leaves of catnip and silver vines, cats increased their release of iridoids. Cats then rub the plants longer,” which promotes their repulsive action on the hair.

The action on the leaves, however, varies between the two plants. Thus, in catarrh, the release of nepetalactone by the damaged leaves increases enormously. In the silver vine, the crumpled leaves do not produce the same “cocktail” of iridoids as the intact ones. It is then very effective against mosquitoes, even at low concentrations.

Graphic study summary. The “silver vine” corresponds to the silver vine and the “catnip” to the cataire. Credit: Masao Miyazaki & all / iScience

To protect themselves from mosquitoes, naked cats rub against each other, so not just against these plants. They chew them too. A long game-like behavior that could kill biologists through new plant enzymes capable of producing useful plant iridoids against a wide range of crop pests.

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