Cats are so often a mystery even to those who know them best. Why do they sleep so much? Why do they want your full attention one minute and none the next? How can they find their way back house after being stuck miles away years? Writer Haruki Murakami, known for including cats in his novels and essays, once confessed not knowing why he does it; the cat “sort of naturally slips,” he said.
Another mystery: why do cats love catnip? When exposed to a plant belonging to the mint family, majority domestic cats will lick it, rub against it, chew on it, and roll around in it. They are full of euphoria, getting high from this substance. They also go crazy for other plants, especially the silver vine, which is not closely related to catnip but causes the same reaction in felines, including big cats like jaguars and tigers.
For years, this behavior has been another mystery associated with cats. But new researchpublished Tuesday in the journal iScience, suggests the reaction to catnip and silvervine could be explained error repulsive Effect iridoids, chemicals in plants that cause a high.
Researchers led by Masao Miyazaki, an animal behaviorist at Iwate University in Japan, found that the amount of these iridoids released by the plant increased by more than 2,000 percent when the plant was damaged by cats. So maybe a kitten’s high provides an evolutionary advantage: it repels blood-sucking insects.
Christine Vitale, a cat behavior expert at Unity College who was not involved in the study, said the study builds on strong previous work. Last year, the same lab published a study showing that cats would go out of their way to coat themselves in DEET-like iridoids.rolling over the chemicals or getting up to press your cheek against them. “This indicates that physical application of the compounds to the cat’s body may be beneficial,” Dr. Vitale said.
Carlo Siracusa, an animal behaviorist at the University of Pennsylvania, who was also not involved in the study, agrees. “Evidence shows that they want to permeate their bodies with scent,” he said. But, he added, “keep in mind that a significant proportion of cats do not exhibit this behavior. So why were they chosen this way?”
As an evolutionary adaptation, iridoids that repel insects probably doing more to protect plants from herbivorous insects than to help cats avoid insect bites. Plants often release irritants when damaged to help repel an attack, and they release other chemicals that signal danger to their neighbors. “Plants are masters of chemical warfare,” said Marco Gallio, a neuroscientist at Northwestern University who was not involved in the new study.
Last year, Dr. Gallio and his colleagues published a report this linked the main insect repellant in catnip, nepetalactone, to a receptor protein that irritates mosquitoes and related insects. The receptor, which is also present in humans and cats, can be activated by tear gas. But Dr. Gallio found that while nepetalactone did not adversely affect humans and cause ecstasy spasms in cats, it activated this particular receptor (called TRPA1) in many insects—an added bonus for cats rolling around in their favorite drug.
In their latest study, Dr. Miyazaki and his colleagues measured the chemical composition of the air directly above the leaves – both intact and damaged – of catnip and silver vine. They then measured the level of iridoids in the leaves themselves. They found that catnip leaves mutilated by cats secrete at least 20 times more nepetalactone than whole leaves, and damaged silvervine leaves secrete at least eight times more of these iridoids than whole leaves. Cat interactions with silvervine also changed the composition of the plant’s insect-repellent cocktail, making it even more potent.
After the cats have rubbed their muzzle and body against the plants, they are sure to be covered with a durable layer of Pest Begone.
This finding, combined with previous research by Dr. Miyazaki and his team, confirms emerging claims that at least part of the benefit of the catnip craze is to prevent mosquitoes and flies. This behavior, called “self-anointing,” would not be the first of its kind in the animal kingdom. Mexican spider monkeys are known to smear yourself with various types of leaves, probably for social or sexual purposes, and hedgehogs often rub in toxins on their thorns.
However, many questions remain to be answered, including why only felines seem to show a euphoric reaction to catnip and silvervine, and why only some of these cats do so. Dr. Gallio, enthusiastic about the new study, offered a cautious approach. “What do I know?” he said. “I wasn’t there to see how evolution happens.”