At the height of the 2003 season, more than 100,000 tons of hairy crabs marked with the Yangcheng Lake imprint were sold. Yet the Yangcheng Lake Crab Trade Association report for that year claimed the output of the lake was 1,500 tons.

Ingenious methods of detecting fakes have been developed. One involves placing a live crab on a glass table. The jist of the exercise is to test leg strength. While other lakes have a silty bottom that allows the crabs to feed while remaining stationary, the hardpan of Yangcheng means the crabs must move around. If a crab can scramble on the table with power and velocity, it is considered more likely to be authentic.

Mr. Wang of Delight Crabs is most concerned about pollution and "overfishing the lake." In the past year, the practice of "dining boats" — where parties could have crabfests on the lake — has been stopped. "We have been taking too much from Yangcheng," he says. "This one lake can't satisfy all of China."

Crabs have a strong claim on the Chinese imagination. In the popular film "The Joy Luck Club," about the success of four first-generation Chinese-American families, the narrator always ruefully respects the elaborate rituals her mother adopts when serving crab.

The crab has also been a metaphor for tyrannical or duplicitous behavior. During the Cultural Revolution, the infamous "Gang of Four," including Mao's wife, Jing Qing, were known in street lingo as "the crabs."

The moniker referenced a lack of straightforwardness as the gang conducted highly personalized purges and other extreme behaviors.

Just so, crabs rarely move back and forth, but scuttle adroitly from side to side, in ways difficult to predict and follow.