The Amazonian Snail a name that evokes an exotic paradise.

Even in Chinese, in which it is known as Fu Shou Luo, the name has good connotations, indicating felicity and longevity.

But over the past few weeks the snail has fallen short of the ideal its names conjure up, wrecking havoc in both humans and rice fields.

Since June, 87 Beijing residents have been infected with Angiostrongylus cantonensis, a lungworm parasite commonly carried by snails and slugs, after dining on half-cooked Amazonian snails.

The victims have all shown different symptoms, some suggesting meningitis. They suffer from headaches, stiff necks, tingling or painful sensations in the skin, low-level fever, nausea and vomiting.

Meanwhile, the freshwater snails are thriving in China's paddies.

More than 170,000 hectares of rice paddies in South China's Guangxi Zhuang Autonomous Region are being devoured by them.

Overnight, Amazonian snails have became a buzzword in the press and an enemy of the state.

The mollusc, originally from the floodplains of South America, was first introduced into China as a food source by Taiwanese traders in 1979.

Many farmers reared them, but abandoned them later because the taste failed to meet consumer demands, according to Dr Ravindra Joshi, chief scientist at the Philippine Rice Research Institute (PhilRice).

Joshi is a world expert on the Amazonian snail and has published a number of books and papers about the mollusc.

One of the world's 100 most devastating invasive alien species, the snail later started to damage rice paddies, mainly because of its high reproductive rate and voracious appetite.

A female Amazonian snail can lay 50 to 500 eggs at one time, with an 80 per cent hatch rate. The snail can withstand drought for several months and moves only when the water level reaches half its shell height.

As long as there is water in the field, the snail can destroy newly transplanted or direct-seeded rice very quickly.

"It cuts the base of young seedlings with its layered teeth and munches on the tender sheathes of rice," writes Joshi in one of his papers, published in 2005.

Lei Hongguang, a farmer in Hengxian County in Guangxi, is one witness of how ravenous the snails can be. "More than half of my rice seedlings were bitten off within three days," he told the Xinhua News Agency.

According to Joshi, the extent of damage that the snail can do to a rice crop depends on its size and density, and the growth stage of the rice plants. Three snails in a square metre of rice field can cause significant losses.

"Once Amazonian snails have invaded, they are difficult to eradicate," Joshi told China Daily.

His words are best illustrated by China's fight with the invasive pest over recent decades.

In 1988, the snail was first recorded in 37 counties of Guangdong Province, affecting about 1,700 hectares of rice paddies.

Nie Chengrong, an associate professor with South China Agricultural University in Guangdong, recalled that the serious damage continued in the area until the mid 1990s and expanded across southern China with the increasing amount of direct-seeded rice production.

Statistics show that no less than 100,000 hectares had suffered from the pest during the period.

"Farmers had to use mollusc pesticides or simply remove them with their bare hands," Nie said.

The problems were reduced with the use of pesticides until the recent outbreak in Guangxi and Beijing.

Farmers in Guangxi are now trying different ways to kill the pest, including using pesticides and camellia tea powder, one of the country's traditional methods of fighting rice pests and diseases.

But pesticides can also kill other creatures such as fish, and camellia tea powder is not a good way of controlling the snail, said Joshi.

Deng Hanqian, a farmer in Guangxi's capital city Nanning, told Xinhua that the use of tea powder had raised growing costs by about 300 yuan (US$37.5) per hectare, despite its effectiveness.

Handling an Amazonian snail with bare hands is also risky, Joshi said, because of possible infection from parasites.

In some affected areas, ducks and fish are freed into the paddies to eat the snails. This is considered an ecological approach to fighting the pest. But both Joshi and Nie agree it is not an effective solution because they only eat small snails.

According to Joshi, a wider variety of methods have been developed to control the snails in transplanted rice fields than in direct-seeded rice paddies.

"Three things are most important to regulate snail damage in transplanted rice fields," he said.

Farmers need to use well-levelled fields to maintain a shallow water depth after transplanting for two to three weeks, and use stronger seedlings.

The use of attractants, such as vegetable waste or old newspapers, in water-logged areas in rice fields is also telling, he added.

However, he said: "The challenge of controlling Amazonian snails in direct-seeded rice fields has still not been answered."

The expert is now working together with his colleagues at PhilRice to develop new techniques to address the problem.

Meanwhile Beijing has issued an immediate suspension on any purchase, sale or processing of the snail. Violators will be fined a maximum of 30,000 yuan (US$3,750).

Nie, the Guangdong-based agriculturist, advises the government to impose stricter regulations on domestic snail breeding farms. "It is important not to free the snail into public water systems. Otherwise it will move into rice paddies," he said.

However, as both agricultural experts and doctors point out, Amazonian snails, also known as golden apple snails, can be a safe and nutritious food if completely cooked. "They are high in protein content," said Joshi.

Besides, the snail has proved to be an effective "biological weed killer" for farmers in Japan, the Philippines and South Korea, according to Joshi.

(China Daily 08/28/2006 page1)