I never liked cats much. Then Mother moved into my barn.

Before Mother, I was never much drawn to cats. They seemed slithery and remote. I have a farm, and cats didn't appear to be useful.

I am partial to working dogs—especially border collies and Labradors—that can herd sheep, fetch sticks, hike with me, cuddle on the sofa, and swim in nearby streams. I didn't really get having an animal you couldn't herd sheep or take a walk with.

Then the rats came. They invaded my farm last summer, especially the big barns. They were fat—at first, I mistook one for a rabbit—arrogant, and fearless. The farmers told me there was nothing much to be done: Rats, naturally drawn to farms, were smart, hardy, and tough to get rid of, especially with other animals around.

They had countless holes in stone walls and rotted silos to nest in. They figured out traps. And I couldn't spread poisons around a barnyard full of sheep, donkeys, chickens, and dogs. A farmer friend suggested a barn cat. He was about to weed out his own posse, and had one in mind for me, because she was used to dogs. She was young and scrawny and got her name—Mother—from her habit of caring for kittens, whether they were hers or not.

Where I live in upstate New York, barn cats are mythic. Elusive and reclusive, they prowl barns and pastures, sleep in haylofts, and make war on rodents and snakes.

They die often and—frequently—brutally, from disease and neglect, from attacks by predators like foxes and coyotes, from target practice by kids or hunters, or from the bites of rabid raccoons. They get hit by cars or, in the worst cases, waste away from starvation and exposure. When their numbers grow—few are spayed or neutered—they often are shot. Some of the softer farmers put heat lamps in their barns or let their barn cats into basements and mudrooms on subzero nights. Most don't.

Did I need a barn cat?

Rose, my 2-year-old border collie, ran the farm and didn't like cats. And a farm needs the right balance of animals. But the rat population was booming. So, with many misgivings, I agreed to take Mother. My neighbor drove her over in a cardboard box, a stringy, mottled brown and black creature that looked the worse for wear. I had the distinct feeling that if I hadn't taken her, she wasn't headed for a shelter.

Mother was surprisingly friendly. She took to me right away; she loved to be stroked and scratched, and she purred when she saw me. She was always ravenous and seemed astounded by the cans of cat food I ferried out to her in the barn. She was also instantly businesslike, scoping out the rats and the mice the second she arrived.

I took her to the vet and had her spayed, then put a collar on her, so strangers would know she was owned.