Some people think oysters are slimy and taste far too salty. For others, they're a delicacy. Oysters may provoke a love-hate response, but they also have impressive ecological properties, and the leftover shells have been used in some surprising ways. Here are 9 fascinating facts about the bivalve.

1. Oysters have been around since the Triassic period.

Oysters first appeared over 200 million years ago, when the earliest dinosaurs roamed Pangaea. Evidence of human oyster consumption dates back to about 164,000 years ago, according to a 2007 paper in Nature describing human ancestors’ first modern behaviors. A 2013 study found that Stone Age people in Denmark ate so many oysters that piles of the discarded shells show a marked decrease in the bivalves’ size over the years.

2. In the Victorian era, oysters were the food of the poor, not the rich.

Pickled oysters were liberally consumed by London’s poor. They were sold as bar snacks and by stalls on street corners, and for those who couldn’t afford beef or mutton, oysters made up the protein in soups and stews. Oyster pie was also a popular dish with the lower classes.

3. A Scottish estuary once held the world’s largest native oyster bed.

The oyster-free Firth of Forth, Scotlandgeorgeclerk/iStock via Getty Images

Covering more than 150 square kilometers (about 58 square miles), the oyster bed of the Firth of Forth on Scotland’s east coast, near Edinburgh, was a veritable gold mine of shellfish. Historians estimate that 30 million oysters could be harvested from it annually in the 1700s, to be sold in London and Europe. Sadly, over-harvesting meant that the oyster bounty from the Firth of Forth couldn’t last. By the late 19th century the beds were badly depleted, and only around 1200 oysters were harvested per year. Today there are no native oysters in the Forth.

4. Discarded oyster shells were used to build cities.

Speaking of Edinburgh, remnants of oyster shells found in walls have offered clues to Edinburgh’s culinary past. Residents of the Scottish capital reportedly put away 100,000 oysters daily during the 17th century, and walls containing oyster shells were uncovered during work on tenement buildings in the city. The shells, which appear to have been used as a filler between stone and brick, most likely came from a tavern located in the basement of the building, as oyster shells were typically left to pile up on floors.

5. A contaminated oyster killed the Dean of Winchester Cathedral.

Oysters glean nutrients from seawater as it passes through their gills. They can filter more than 50 gallons of water a day, leaving a cleaner environment. But oysters can also be contaminated by substances in the water, and they developed a dangerous reputation in early 20th century England thanks to increasing water pollution. In 1902, the Dean of Winchester attended a mayoral banquet where oysters were served. The shellfish had been harvested from the Hampshire village of Emsworth, where a sewage spill had occurred, and the dean and several other guests died of enteric fever following the dinner. The food poisoning scandal devastated the oyster trade in Emsworth, leaving many jobless.

6. Baltimore oyster packers invented a knife called the “Chesapeake stabber.”

The Baltimore area came to dominate the American oyster industry in the 19th century, with 90 percent of the country’s oyster packing industry—more than 100 companies—located in the Maryland city. Whole oysters were shipped by railroad from Baltimore to inland cities on ice. Later, canning extended the oysters’ shelf life and allowed them to be shipped greater distances cheaply. The packers developed a particular kind of oyster knife known as the Chesapeake stabber, with a straight, sharp, thin blade meant to separate the shells through the oyster’s lip. Today’s champion shuckers still use the Chesapeake stabber in their trade.

7. A local escargot shortage led to a classic oyster dish.

Oysters (not snails) Rockefellersbossert/iStock via Getty Images

In 1889, a snail shortage drove the son of the founder of the famed New Orleans restaurant Antoine’s to get creative with an appetizer. He substituted oysters for snails, and Oysters Rockefeller was born. In this dish, instead of being served raw, the oysters are baked in the half shell along with spinach, butter, breadcrumbs, and herbs. Why “Rockefeller”? The story goes that a patron commented that the oysters tasted as rich as their namesake.

8. Oyster shells are recycled to help buffer coastlines from climate change.

The Coalition to Restore Coastal Louisiana launched an oyster shell recycling program in 2014, the first such initiative in the state. The shells are returned to the water to restore oyster reefs, which protect shorelines from erosion and storms. The oysters’ rough, ridged shells provide extra surface area to absorb wave energy better than dykes and levees; plus, the reefs provide a place for baby oysters to anchor themselves. The program has collected more than 4000 tons of shells so far.

In New York City, the Billion Oyster Project is restoring 100 million oysters to New York Harbor to mitigate the effects of storm surges. Organizers hope that the oyster beds will reduce flooding and provide a cleaner environment (through their filter feeding) for other species.

9. The jury’s still out on whether oysters are aphrodisiacs.

Oysters are particularly rich in zinc—which is known to be vital for sexual function in men—and have been thought of as aphrodisiacs for centuries. (Not to mention their resemblance to female genitalia.) Renowned seductor Giacomo Casanova supposedly ate multiple oysters for breakfast daily, suggesting he viewed the mollusks as "the nectar of the gods." These days, scientists remain unconvinced that there is a clear relationship between oysters and libido.