Even for the most aloof cats, just a few leaves of catnip can trigger excited bouts of chewing, kicking, and rolling.
Silver vine or matatabi in Japanese, it inspires a similar plant-induced euphoria in our feline friends. The answer sure sounds funny, but until recently, scientists weren’t sure if cat behavior could actually have other benefits beyond pure pleasure.
New research, published this week on iScience, suggests that when cats play (and harm) catnip or silver vine, plant leaves actually emit higher levels of chemical compounds that have one benefit: repelling mosquitoes. Both plants can act as a kind of natural bug spray, and when cats chew the leaves, that bug spray becomes even more effective. Researchers at the University of Iwate in Japan, who have been studying cat interactions with catnip and silver vine for several years, were behind the research..
But rolling in the leaves is only one component of cats’ response to these plants. Masao Miyazaki, an animal behaviorist at Iwate University and author of the study, explained that cats behave in four main behaviors with catnip or silver vine: licking, chewing, rubbing and rolling. In a previous study, Miyazaki says he found that rubbing and rolling are very important in transferring iridoids, the chemicals that trigger the cat’s endorphin discharge, onto the cat’s fur and repel mosquitoes. If rubbing and rolling in silver grape leaves is a cat’s way of applying bug spray, that still doesn’t explain why, in addition to getting high, cats also lick and chew the leaves.
In the new study, the researchers took a closer look at what happens chemically when leaves are damaged by cats. First they collected intact silver grape leaves, leaves that had been chewed by cats and leaves that they crumpled by hand. A chemical analysis showed that the damage inflicted by both cats and humans caused increased emissions from the leaves of various iridoids. The chemical cocktail in the damaged leaves was also less dominated by a single chemical and instead had a more uniform balance of five different chemicals.
The researchers then tested these different chemical cocktails to see how the cats and mosquitoes responded to them. When they received trays with intact and damaged silver vine leaves, the cats spent more time licking and rolling on the damaged leaves. And when the researchers synthesized the chemical cocktails found in these leaves, the cats again spent more time with the damaged leaf cocktail.
Cats preferred the more balanced blend of iridoids over the simpler blend, even when the levels of nepetalactol, the main iridoid in the silver vine, were the same. It was previously thought that nepetalactol was what attracted cats, but this new discovery revealed that there was something special about the chemical blend that was more tempting. “I was really surprised that the combination of iridoid compounds improved the feline response,” says Reiko Uenoyama, a graduate student at the University of Iwate and lead author of both studies.
The complex chemical mixture that was more attractive to cats was also more repellent to mosquitoes. To compare the insect repellent properties of the mixes, the researchers filled a transparent box of mosquitoes and placed a shallow dish inside. When the complex chemical mixture of the damaged leaves was added to the pot, the mosquitoes fled faster than when the simpler mixture of the intact leaves was added.
While the silver vine reacted to the damage inflicted by the cat by diversifying its chemical profile, catnip did not. The researchers repeated all their experiments with catnip and found very different results. The main iridoid chemical in catnip is nepetalactone, not nepetalactol, and this remains the case regardless of leaf damage. When cats chew catnip, the leaves greatly increase their nepetalactone emissions alone.
Despite this different reaction to damage, being crumpled still made catnip leaves more attractive to cats and more repellent to mosquitoes. But in this case, the responses were due to higher levels of a single chemical. And when comparing plants to each other, a large dose of the catnip cocktail was needed to trigger the same response from cats and mosquitoes as a very small dose of the silver vine cocktail. Yet catnip leaves themselves were as attractive to cats as silver vine leaves because the amount of chemicals that catnip leaves emit is much higher overall.
Why even small amounts of complex mixtures of chemicals are so effective in triggering responses is not clear to scientists. “Unfortunately,” says Miyazaki, “we don’t know why the cocktail reacted more strongly to cats and mosquitoes.” But despite these persistent questions, Benjamin Lichman, a plant biochemist at the University of York who was not involved in the study, says this research “highlights the importance of chemical mixtures or cocktails in interacting with animals compared to individuals. compounds “.
Scientists are still not sure when this particular cat behavior first evolved. In their previous study, the researchers found that leopards and jaguars rub their heads on nepetalactol-soaked paper just like house cats do. This finding suggests that this behavior that takes advantage of the insect repellent characteristics of some plants may have evolved into a distant feline ancestor.
“I find it so interesting how cats developed this innate defending behavior in this way,” says Nadia Melo, a chemical ecologist at Lund University who was not involved in the study. She points out that other mammals face similar disease risks from insects, “but you don’t see that in dogs, who are obviously also affected by mosquitoes.”
Catnip and silver vine could also be useful in protecting humans from insects. The mosquito species used in this study transmits roundworms to cats and dogs and also spreads many human viruses, such as dengue and chikungunya. And Melo’s previous research suggests that other mosquitoes are likely to have similar answers. “I think all mosquitoes would react in much the same way,” he says.
So the chemicals in catnip and silver vine could prove useful in developing safer and more effective insect repellants for human use. They could also have the side effect of attracting cats. “If someone doesn’t like cats or is allergic to cats,” Miyazaki writes in an email, “they shouldn’t use iridoids as a repellent!”