Anyone who has seen a cat experience catnip knows that it makes them go a bit wild—they rub in it, roll on it, chew it, and lick it aggressively. It is widely accepted that this plant, and its Asian counterpart, silvervine, have intoxicative properties, but this might not be the only reason why cats rub on and chew the plants so enthusiastically.
Researchers in Japan have found that when cats damage catnip, much higher amounts of strong insect repellents are released, indicating that the cats’ behaviour protects them from pests. They have published their findings in iScience.
Catnip and silvervine leaves contain the compounds nepetalactol and nepetalactone, iridoids that protect the plants from pests. To see how cats’ behaviour was affecting the chemicals released by the plants, Professor Masao Miyazaki at Iwate University worked with chemists at Nagoya University.
“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, but their composition changed in ways that seemed to encourage the cats.
“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,” Professor Miyazaki said.
“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 Aedes albopictus mosquitoes. 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 silvervine leaves makes it more repellent to mosquitoes at low concentration.
To test if the felines were reacting to these compounds specifically, the cats were given dishes with pure nepetalactone and nepetalactol.
“Cats show the same response to iridoid cocktails and natural plants except for chewing,” Professoir Miyazaki said.
“They lick the chemicals on the plastic dish and rub against and roll 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. This means that licking and chewing is an instinctive behaviour elicited by olfactory stimulation of iridoids.”