Do mice fear the scent of a cat? Do mice really love cheese? Why isn't there mouse flavor cat food?

February 1, 2008

Dear Cecil:

Do mice fear the scent of a cat? Does just having a cat reduce the chance of rodent infestation? -- Ayten Osmanli

Do mice really have a particular fondness for cheese, as cartoons tell us? -- Enyce

Why don't they make rat- or mouse-flavoured cat food?

For generations reared on Tom & Jerry and their ilk, the story of the mouse's struggle for its place in a universe of cats and cheese has acquired a resonance to rival the great themes of mythology and literature. But how much of the saga as we understand it is accurate? Let's run it down.

  • Mice and cats. Generally, yes, the scent of a cat, even one that's a crummy mouser, should help keep mice away. Over the millennia, mice and rats have evolved a strong aversion to the smell of cats and other predators; laboratory-bred rodents hundreds of generations removed from the wild will freak out upon catching a mere whiff of cat. Unless, of course, they're somehow reconfigured not to. In a study published late last year, for instance, Japanese researchers reported on a strain of mutant mice they'd whipped up that lacked certain crucial mechanisms for interpreting odors. These mice could smell cats just fine, but didn't know they were supposed to be afraid: confronted with a cat, they chose to investigate or even try to play rather than flee.

    Another exception that proves the rule is the case of the parasite Toxoplasma gondii, discussed here a couple years back when the topic was a possible link between cat poop and schizophrenia. A quick recap: T. gondii infects a variety of mammals, including rats, but can reproduce only when the host animal is a cat; one of its evolutionary tricks is to make infected rats act weird, improving their odds of being caught by cats and thereby allowing the parasite to spread. A key form of said weird behavior: T. gondii-infected rats not only fear cat odor less, they're actually drawn to it. So, since about a third of wild rats carry the parasite, having a cat in the house will repel the majority of rats but might encourage some in the minority to stop by.
  • Mice and food. As anyone who's found himself sharing living quarters with a mouse can attest, mice are opportunistic eaters: if something's got even a speck of nutritional value, it's on the menu. Cheese has been considered a staple of the foraging mouse's diet at least since Aesop was writing fables, and there's no reason to think that it would make particularly poor mousetrap bait. But according to a 2006 UK study, cheese is actually too low in sugar to be a mouse's first choice of food; given their druthers, mice tend to prefer things like grains and fruit - the kind of stuff they're likely to run across in nature as well as in the pantry. So maybe mice and their interests have been misrepresented all this time, but good luck getting animators to change their MO: for classic cartoon iconography, you can't do much better than the time-honored wedge of Swiss.
  • Mice as food. OK, Simon - har har. But just in case you're serious, consider that: (1) A cat fending for itself in the wild hunts mice not necessarily because of the irresistible taste but because that's what's around to be caught. If it had any chance of landing a tuna, it might well give the mice a pass. (2) A cat that's fed by humans hunts mice because it's (a) instinctive and (b) fun. And, crucially, (3) what goes into the average can of cat food has at least something to do with what's left over after they make the human food, and for whatever reason mouse meat has never really won many fans at the top of the food chain.

Which isn't to say there aren't plenty of people who can tell us what mouse tastes like. In his Never Cry Wolf (1963), Canadian naturalist Farley Mowat writes of eating mice, calling the flavor "pleasing, if rather bland." Vermont biology professor Bernd Heinrich, who apparently acquired a taste for mouse as a child in postwar Germany, has described treating his students to breaded mice braised in olive oil; "They're like anything," he told one interviewer, "if you know how to prepare them." And these guys were hardly pioneers: the ancient Egyptians fed cooked mouse to children suffering from teething pains, and roasted mice were long prescribed as a cure for bed-wetting. Such folk remedies, remarkably enough, persisted well into the 20th century - as of the late 1950s a schoolteacher in London's East End reported that young bed wetters there were made to drink water in which a mouse had been boiled. So on the off chance that anyone reading is still serving the kids mouse tea: for God's sake, stop.

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