Snails Be Gone

Introducing new species to an ecosystem can wreak havoc. Golden Apple Snails were released in canals and waterways in the Philippines 10 years ago to be harvested as a local food crop and for export. But the snails did the most feasting. They consumed newly transplanted rice plants, then compounded the problem by breeding rapidly. During drought periods they hide in the soil-- making them difficult to detect.

Golden Apple Snails are now one of the worst pests of rice in SouthEast Asia. At first, farmers tried to control them with pesticides: Aquatin, Brestan, Telustan and other molluscicides. These chemicals injured the health of people and animals. They caused nails and hooves to fall off, and swelling in the genitals as well as sore eyes. In October 1990, the Fertilizers and Pesticides Authority banned the harmful chemicals. Instead of using chemicals, farmers tried picking the adult snails off rice plants and introducing ducks to eat the snails, but to no avail. Neither farmers nor ducks can keep up with the snail, which eats voraciously and lays up to 300 eggs per week.

Fish -- carp and tilapia in particular-- may be able to slow the onslaught of snails. In aquariums and rice fields in the Philippines, carp and tilapia eat young snails, but not adults. The immediate effect of the fish on crop yield is uncertain because it is the adult snails that damage the rice plants. In the long run, fish may reduce the number of snails that reach adulthood.

Fish alone cannot solve the problem. Farmers may have to use additional methods, such as those suggested by the Farmers Outreach Program in Butuan City. These include putting a screen in the water inlet to the paddy; sticking wooden stakes in and along the canal where snails will lay their eggs--these can be collected and crushed; letting ducks into the paddy to eat snails except during the planting season and more.

Offering farmers an alternative to spraying, instead of simply telling them to stop, makes IPM more effective. Farmers will be reluctant to spray if they know that they will kill fish that are eating snails and saving their rice crop.

BBC Farming World Program, Radio Scripts, Nov 17, 1992.


Dr. Matthias Halwart
International Rice Research Institute
P.O. Box 933