Cats love catnip. They go weird for it. Even the most dignified and solemn felines go daffy in the presence of this plant – rubbing themselves in it, rolling on it, chewing it, dancing deliriously around it, and even licking it aggressively.
But while it has long been understood that catnip, and the similar Asian plant silvervine, have intoxicative properties, new research has found that cats’ instinctive response to the presence of catnip could be unwittingly helping the plant release chemicals which act like an insect repellent and could benefit cats.
Lead author of the research Masao Miyazaki, an animal expert at Iwate University in Japan who specialises in how chemicals drive animals instinctual behaviours, said cats’ reaction to catnip and silvervine was so universal across the world that he “had to know what was going on”.
He said: “Even in the famous musical Cats there are scenes where you see a cat intoxicate another cat using catnip powder.”
Catnip and silvervine leaves both contain the compounds nepetalactol and nepetalactone, from a chemical group called the iridoids that protect the plants from pests.
To see how cats’ behaviour was affecting the chemicals released by the plants, Professor Miyazaki worked with chemists at Nagoya University to measure the emission levels of these iridoids before and after the plant’s leaves were damaged by the intoxicated cats.
“We found that physical damage of silvervine by cats promoted the immediate emission of total iridoids, which was 10-fold higher than from intact leaves,” Professor Miyazaki said.
Not only were more iridoids released through the cat’s physical manipulation of the plants, but the scientists found the chemical composition of the iridoids changed in ways that seemed to encourage the cats’ behaviour further.
“Nepetalactol accounts for over 90 per cent of total iridoids in intact leaves, but this drops to about 45 per cent in damaged leaves as other iridoids greatly increase,” said Professor Miyazaki.
“The altered iridoid mixture corresponding to damaged leaves promoted a much more prolonged response in cats.”
In previous work, Professor Miyazaki and his team showed that these compounds effectively repel a particular species of mosquito – the Aedes albopictus mosquito.
Now the team has shown that when cats damage the plants by rubbing, rolling, licking, and chewing, the repellent properties are even more effective. The diversification of iridoids in damaged silver vine leaves makes it more repellent to mosquitoes at low concentration.
To test if the cats were reacting to these compounds specifically, the cats were given dishes with pure nepetalactone and nepetalactol.
The team found this did seem to be the case.
“Cats show the same response to iridoid cocktails and natural plants except for chewing,” said Professor Miyazaki. They licked the chemicals on the plastic dish and rubbed against and rolled over on the dish.”
“When iridoid cocktails were applied on the bottom of dishes that were then covered by a punctured plastic cover, cats still exhibited licking and chewing even though they couldn’t contact the chemicals directly,” said Professor Miyazaki.
“This means that licking and chewing is an instinctive behaviour elicited by olfactory stimulation of iridoids.”
The team said they are now aiming to to understand which gene is responsible for cats’ reaction to catnip and silvervine.
“Our future studies promise to answer the key remaining questions of why this response is limited to cat species, and also why some cats don’t respond to these plants,” said Professor Miyazaki.
The research is published in the journal iScience.
