In their most recent study, Dr. Miyazaki and his associates measured the chemical composition of the air immediately above leaves — both intact and damaged — of catnip and silver vine. Then they measured the iridoid levels in the leaves themselves. They found that catnip leaves mangled by cats released at least 20 times more nepetalactone than intact leaves did, while damaged silver vine leaves released at least eight times the amount of similar iridoids than did intact leaves. The cats’ interactions with silver vine also changed the composition of the plant’s bug-repelling cocktail, making it even more potent.
After rubbing their faces and bodies against the plants, cats are sure to be coated in a robust layer of Pest Begone.
This finding, paired with Dr. Miyazaki and his team’s previous research, supports nascent claims that at least part of the benefit of the kitty catnip craze is to stave off mosquitoes and flies. Such behavior, called “self-anointing,” would not be the first of its kind in the animal kingdom. Mexican spider monkeys have been known to smear themselves with different kinds of leaves, probably to serve a social or sexual purpose, and hedgehogs often rub toxins onto their spines.
Still, there are many questions left to be answered, including why seemingly only felines exhibit a euphoric response to catnip and silver vine, and why only some of these felines do so. Dr. Gallio, while enthusiastic about the new study, offered a cautious approach. “What do I know?” he said. “I wasn’t there to see evolution happen.”