The McDonald's McRib sandwich is a ghost. It will appear at a location for a few weeks at a time, and then, tragically and unexpectedly, it will disappear. The sandwich, a "boneless pork patty molded into the shape of a rib slab and adorned with pickles, onions and barbecue sauce on a bun," according to The Wall Street Journal, has floated through McDonald's menus since 1981. In November, the sandwich will appear on all McDonald's menus for the first time. Yet wait just a month and a half—it'll be gone again.

Naturally this disappearing act has tugged at the heartstrings of McRib fans, who have quietly developed a surprising loyalty to their favorite fast-food pork sandwich:

Nearly 300 Facebook groups are devoted to the sandwich, including "Bring back the McRib, Please," with more than 500 members.

Some people don't get the attraction. Justin McDaniel, a 32-year-old health-care-industry worker in South Pasadena, Calif., says he'll go out of his way for some fast-food products, but the McRib is "pretty disgusting" and he'll never sample one again.

"It's a conglomeration of pork waste, as far as I can tell," says Kate Sedgwick, 34, a travel blogger who lives in Buenos Aires, Argentina. She has never actually tasted a McRib, and isn't familiar with its ingredients because, she says, "I saw a dog turn his nose up at a piece of one. That's all I need to know." ...

Alan Klein's obsession with the McRib began when he was growing up on a hog farm in South Dakota. The 28-year-old meteorologist, who now lives in Minnesota, justified his craving by saying that eating McRibs supported the family business.

After moving to Minnesota for college, he had trouble finding McRibs. Five years ago, he visited South Dakota and saw the sandwich at a McDonald's near his childhood home. "It rekindled my love of McRibs and made me start thinking it would be nice to know where they were," he says.

Three years ago, he launched the McRib Locator at www.kleincast.com. Visitors can inquire about and report McRib sightings. Mr. Klein says he gets 300 to 400 hits a week.

Read more at The Wall Street Journal.