When it comes to producing fibers for human clothing, silkworms are nature’s hardest-working larvae. But they’ve got competition — in fact, reports the BBC’s Max Paradiso, the world’s rarest silk actually comes from clams.

Paradiso profiles a woman named Chiara Vigo, who is thought to be the only person left on Earth who knows how to harvest, spin and fabricate materials from what is known as sea silk. The thread, which is also called byssus, is secreted by large clams, which produce it to attach themselves to rocks. Think of it as a sort of “solidified saliva,” says Paradiso.

Vigo, who lives on the island of Sant’Antioco in Sardinia, dives 300 to 400 times while accompanied by Italian coast guard members who make sure she does not disturb the protected species, reports Paradiso. Then, she spins the thread and makes it into glistening bracelets, lace and other garments. Since it’s so rare and comes from protected species, writes Paradiso, it’s not for sale.

Be sure to check out Paradiso’s profile of Vigo for more information on how she harvests and weaves the fabric and how she’s upholding ancient traditions at the same time. The photos are breathtaking, and it highlights just how delicate it is to take a product from sacred sea spit to shimmering rarity.