Cats' love of catnip is written into the name, but the reasons for this love aren't what you probably think. The fondness our companions and their larger relatives have for catnip's molecules isn't shared by insect pests. Getting a good faceful can help protect against unpleasant bites, and probably disease too.
Given the Internet's feline fixation, it's unsurprising videos of cats going wild on catnip have been watched millions of times. Nevertheless, science long neglected its duty to tell us why they love it so much, although the involvement of the chemical nepetalactone was suspected. Professor Masao Miyazaki of Japan's Iwate University has now addressed this important deficit in our knowledge.
Miyazaki started by noting these effects silver vine (Actinidia polygama) produces a similar response to catnip (Nepeta cataria), and also contains some common chemicals. "The first appearance of silver vine ("Matatabi" in Japanese) as a cat attractant in literature in Japan dates back to more than 300 years ago,” Miyazaki said in a statement. Western biologists caught on fifty years later. “A folklore Ukiyo-e drawn in 1859 shows a group of mice trying to tempt some cats with a smell of silver vine,” Miyazaki added.
Miyazaki and colleagues report in Science Advances that they presented paper filters soaked in chemicals extracted from silver vine to both cats and other members of the cat family, including the jaguar, Amur leopard, and Eurasian lynx. All felids rubbed their faces in the filters dosed with nepetalactol before rolling on the ground. Moreover, the cats subsequently had raised β-endorphin levels in the blood, indicating the molecule was triggering their μ-opioid system. Yep, these are opioids for your cat.
However, the authors suspected an evolutionary benefit, given how widespread the response is within the cat family. Noting reports that nepetalactol is a mosquito repellent, they counted how often mosquitoes landed on cats heads depending on whether they had nepetalacol rubbed in their fur. Both in the lab and home environments, cats that had smeared themselves in silver vine or its product were less likely to be troubled by the disease-bearing pests. The mosquitoes, in this case, were Aedes albopictus, but the authors expect a benefit against A. aegypti, carrier of diseases such as dengue and yellow fever – although the more distantly related malaria carriers are less certain.
The findings explain some things – such as why cats seem keener to get catnip or silver vine on themselves by rubbing their faces or rolling on it than to actually eat it. Indeed when the authors put nepetalactol-infused papers on cage walls or ceilings, cats were attracted to them but skipped the post-rub roll. “Rolling is a functional behavior rather than an indicatior of euphoria or extreme pleasure,” the paper concludes.
Nevertheless, much still puzzles Miyazaki. “Why is this reaction limited to cats? Why don't non-feline animals react to the plant?” He asked. “To find answers, we want to identify the gene responsible for the reaction. The findings of this study may be used in various applications, including development of new mosquito repellant products."
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