Before dawn in Goro, on the Adriatic Sea, Massimo Genari drove by the central roundabout, with its sculpture of two concrete clams in a net, and under a billboard of a mollusk donning a crimson royal crown. Wearing waders, he boarded his boat and motored to the lagoon with scores of other fishermen to rake the clam gardens that for decades have transformed this sleepy Italian village off the Po River Delta into a bivalve boomtown.

As the sun rose, Mr. Genari, a leader of the local fishing cooperative, poured his first haul of clams into the basin of a metal sorting machine. The shells clinked like coins falling from a slot machine. But instead of bushels of treasure, he looked with horror at the remains of a massacre, with the guilty parties — marauding armies of invasive blue crabs — caught blue-and-orange-handed as they scurried over the eviscerated bodies of their victims.

“Opened, opened, opened,” Mr. Genari said, as he sifted through shells and avoided the murderous crabs snapping at his fingers. The killers had, he said, laid waste to the baby clams. “Another two months, and that’s it. The clams will be gone.”

Goro’s fishermen, swamped by the insatiable blue crab, are trying to save not only their local cash crop — the meaty verace clam they first imported from the Philippines in the 1980s — but also a good portion of Italy’s beloved spaghetti alle vongole that is made with them.

“We will lose our identity,” said Arianna Zucconelli, 44, a local wholesale fish buyer, who said that Italy without clam sauce would be a much blander place, and that Goro without clams would be a much poorer one. “This town is built on clams,” she said. “Eighty percent of the town won’t have an income.”

Experts aren’t sure how or exactly when the alien crabs first arrived from North America. Some speculate that crab larvae arrived decades ago in cargo ships. Around Goro, years of droughts allowed seawater to seep further into the Po River’s estuaries, making for more brackish pools preferred by the crabs.

Then floods this spring in the Emilia-Romagna region, where Goro is, washed them into the lagoon, where the warm summer water increased the blue crabs’ metabolism and, free of natural predators, they found an all-you-can-eat buffet of local crabs, mussels, oysters and the prized clams.

“The table,” said Eduardo Turolla, a local mollusk scientist, “was set.”

And the battle joined. Around Mr. Genari’s boat, an armada trawls for the blue crabs, pulling what he estimated to be about 10 tons of them daily from the lagoon, though they have also amassed across Italy’s east and west coasts. He pointed out the spongelike pads teeming with eggs on the bellies of females and the way the males held the claws of dismembered crabs in their clutches. He told stories of children rushed from the neighboring beaches to the emergency room with clawed fingers and toes.

“Either they survive,” he said. “Or we survive.”

The Italian government has mobilized a full-scale “if you can’t beat ’em, eat ’em” campaign. Prime Minister Giorgia Meloni served up a platter of cooked blue crabs, as shown in a picture taken by her brother-in-law, Francesco Lollobrigida, the country’s agriculture minister, who recently visited Goro and promised aid. The minister — perhaps best known for warning about “ethnic replacement” of the Italian people, and not its marine life — also posted a video of himself holding a live crab next to a pot and admiring its “optimal” meat.

Supermarkets around the country are promoting them. (“Blue Crab: A Recipe to Save the Seas!”) Seafood companies are trying to export them.

“In particular, to the U.S. market,” said Carlotta Santolini, a founder of Mariscadoras, which has exported containers of blue crabs to a distributor in Miami. She said Mr. Lollobrigida called her to strategize and invited her to promote Italy’s blue crabs at a frozen seafood exposition next month in Spain. But she acknowledged the toughest market may be the domestic one.

“A signora that goes to the restaurant,” Luca Pavani, 56, said after a morning of hunting crabs, “she can’t just start eating with her hands.”

Mr. Genari noted that they were no picnic to prepare either.

“The first time I brought them home to my companion to cook, she was interested and happy to do it,” he said. “The second time, she threw it at my head.”

In the Chesapeake Bay, Marylanders hammer and rip and douse crabs in Old Bay seasoned salt. But Italians, resistant to culinary novelty and mindful of table manners, are trying to incorporate them into the usual frying pan.

At the Locanda Ferrari restaurant, where diners slurped up plates of spaghetti alle vongole and compared notes on their favorite places for eel, Paola Ferrari, 61, scissored the crabs and dumped them in a pan of tomatoes, onions and herbs.

“They don’t really” order it, she said.

At a restaurant across from the fish market, the crabs were not even on offer, though a drawing above the display case depicted crabs being devoured by an octopus and a sharp-beaked curlew.

“Nature will always find a solution,” it read.

“I see no solution,” said Mr. Turolla, the expert.

In the surrounding streets, residents spoke fondly of the easy money of the clam days. “It was like going to the A.T.M.,” Alessandro Milani, 58, said as he built a crab trap. At the Bar dell’Angolo, fishermen drank bottomless Aperols, cursed the crabs and told horror stories about crab attacks on colleagues wading in the shallow water.

“One of them stabbed right through her boots,” recounted Giorgio Bugnoli, 50.

“Who?” his friends asked aghast.

“Luisa!” he said.

Hundreds of blue tubs filled with blue crabs arrived for sorting at Mr. Genari’s cooperative, for either sale or disposal. An enormous aluminum pan used to cook 1,300 pounds of clams for spaghetti alle vongole during the annual clam festival rested on heaps of black plastic nets. The fishermen hope these nets will protect future crops of clams, though they say the crabs have climbed over, dug under and cut through barriers in the past.

The rejected crabs ended up back at the port, which resounded with the sound of constant typing, as thousands of crabs clicked over one another. A forklift rolled over amputated claws and dumped crate after crate of fly-swarmed crabs into a green container labeled: “Material Category 3. Not Destined for Human Consumption.” A truck loaded the writhing freight for delivery to an incinerator up north. More boats, and more blue tubs, came in.

“In the two months we have been fighting the crabs,” Mr. Genari said, “it is like we have done nothing.”

At 3:30 p.m. in the nearby fish market, a siren announced the beginning of the fish auction. Workers loaded dozens of blue tubs on a white conveyor belt that appeared in front of buyers eating cherry ices on bleachers.

The first crabs were small and had no takers.

“No one wants crabs,” one of the buyers said.

The auctioneer, Fabio Bugnoli, 46, wore a thick blue rubber glove and picked up chains of clinging crabs to demonstrate their size and vim. (“They got me twice,” he said, showing off the marks on his thumb.) One buyer who supplied Chinese neighborhoods bought hundreds. Others who supplied restaurants enticed by the prospect of extreme profit margins bought bigger crabs. The prices were so low, the fishermen said, that they barely covered the cost of gasoline or the crab incinerations.

But Ms. Zucconelli, the buyer, suggested Italians might yet develop a taste for crab. She said her mother had found a way to cook them in a red sauce.

“They’re good and sweet. They’re great fried,” she said. “Then again, a slipper is good fried.”