There are seventy-two alpacas grazing the daisy-dotted acreage of Island Alpaca Company in Oak Bluffs. But chances are, the first animal visitors seen upon walking into the enormous barn on the property won’t be one of them.

Newcomers often furrow their brows, puzzled, and ask the staff if the tall shaggy creature with the skinny legs, big ears and knowing, curious face is a male alpaca.

“This is Sudrina,” the staff answers. “She’s our llama.” The only llama.

“Oh,” they say. “I thought something looked different.”

The next question isn’t always voiced aloud, but is easy enough to read on the still-puzzled faces.

Why on earth is there a llama on an alpaca farm? And just one llama at that?

“Really, one of the most common questions we get is what’s the difference between an alpaca and a llama,” Island Alpaca owner Barbara Ronchetti said on Monday morning, shortly before Sudrina was due for her annual shearing. So in 2009, when Ms. Ronchetti purchased three alpacas from a Wrentham farm that was closing down, and was offered the farm’s guard llama as part of the deal, she and the staff decided to bring Sudrina home. That way, visitors would be able to see the camelid second-cousins side-by-side and judge for themselves.

And besides, “Philippe [Morin, former farm manager and current part-time jack-of-all-trades at the farm] said, ‘Well, she’s rather cute,’” Ms. Ronchetti recalled.

More stately than the alpacas, who with their teddy bear faces and fluffy fleeces are best summed up by the word adorable, Sudrina bears more of a resemblance to a camel, another distant relative. Like camels, llamas were bred to be beasts of burden, domesticated by the Incas around 4000 B.C. (alpacas were also Inca-bred, but solely for their fleece). Sudrina weighs 341 pounds and can carry about half of her body weight, whereas even the largest of the male alpacas weighs no more than 200 pounds. On modern farms, llamas are often used as guard animals, as Sudrina was at her former home, tapping into their protective nature to keep sheep, goats and, of course, alpacas safe.

She doesn’t do much guarding now — there are no coyotes or other predators on Martha’s Vineyard and the alpaca herd sleeps outside at night free of worry — but Sudrina keeps herself busy in other ways.

“She’s been getting into the grain barrels a lot,” farmhand Phoenix Russell said, wondering if the llama might have reached 350 pounds by now. Sudrina’s grain-bin exploits are well-known at the farm; she has taught herself to slide open the unlocked door of the bin to reach the bags of grain inside. Ms. Ronchetti suspects that she even knows how to work the lock itself.

“She’s very smart,” Ms. Ronchetti said. “We should get a barn-cam so we can see what she’s doing.”

Sudrina is typically the first to notice an open gate and the first to sneak out onto a grassy pasture when she’s supposed to be in the farm’s viewing area, eating hay. The farm staffers taught her to gently pluck a baseball cap from a volunteer’s head (usually Mr. Morin’s), and Ms. Ronchetti is teaching her to nod “yes” for a snack.

“She doesn’t do that yet, but I’m working on it,” Ms. Ronchetti said.

Unlike the alpacas, Sudrina also takes considerable interest in, well, herself. She studies her reflection in the farm store windows and, if she gets the chance, mirrors.

“I think she thinks she’s a big, beautiful alpaca,” Ms. Russell said. “I always see her looking at herself.”

The llama takes her role as honorary alpaca seriously, too, particularly when new babies are born. She has never been a mother (guard llamas are typically singletons, the better to keep that protective instinct keyed to the flock), and, at fifteen, is a bit too old to bear young herself. But that hasn’t stopped her from becoming a godmother to three generations of Island Alpaca cria.

When an alpaca cria is born, Sudrina is the first to come over and “meet and greet” the new arrival, Ms. Ronchetti said, hovering close to the newborn even when it and its mother have been moved to a baby pen. Sudrina is always patient with the young cria, too, and never spits on them. When they grow older, she even lets them climb on her back.

“Magnificent,” said Mr. Morin, as he finished shearing a year’s worth of coarse — yet still surprisingly soft — fleece off Sudrina. “She’s magnificent.”