Texas Parks & Wildlife Magazine   


Escargot Gone Wild

Channeled applesnails threaten to gobble up state’s rice crops.

Sheryl Smith-Rodgers

Fire ants. Nutria. Feral pigs.

Now meet the channeled applesnail, another potentially invasive species that has federal and state agriculture officials worried. The South American gastropod can grow as large as a tennis ball, reproduce quickly, and consume tender vegetation, including rice seedlings.

Populations of Pomacea canaliculata have been found in 12 locations in Texas, including rice fields and irrigation canals near Houston, bayous adjacent to rice fields and in natural streams. A year-long survey — funded by the U.S. Fish and Wildlife Service, the Texas Commission on Environmental Quality, and the U.S. Department of Agriculture — is underway to determine the snail’s distribution and its potential impact on Galveston Bay wetlands and drainage areas.

The snail has already destroyed countless crops in Taiwan, Philippines, Vietnam, China, Japan, Hong Kong, Thailand, Cambodia and Hawaii.

Approximately 50 species of freshwater applesnails comprise the genus Pomacea. They naturally range from Florida and some Caribbean Islands to Central and South America. In the Everglades, endangered kites feed on the native Florida applesnail (P. paludosa). Aquarium enthusiasts often buy South American spiketop applesnails (P. bridgesi) because they feed on decaying matter.

Applesnails live and breathe underwater through gills, but they also have a lung-like organ that allows them to forage on land. They lay bright pink egg masses on solid objects above water. After hatching, applesnails can be sexually mature within 60 days.

Initially, channeled applesnails were brought to Taiwan in the early 1980s by promoters who touted them as Asian escargot. Growers who raised them for the culinary market were guaranteed to get rich; hence, the snail’s other common name, the golden applesnail.

Tastewise, the applesnail failed, and farmers lost interest. As a result, many snails escaped or were released. Surviving snails found their way to rice fields, where they continue to reproduce and destroy crops.

Similar devastation by the snails has occurred in Vietnam and Hawaii. Since 1992, the Vietnamese government has banned snail farming and funded expensive campaigns to control their spread and educate people about them. In 2003, Hawaii reported a 17 percent decrease in taro crops, largely due to snail infestations.

Near Houston, a few channeled applesnails, likely released from someone’s aquarium, were found in 1989 and ’90. No more surfaced until July 2000 when some were discovered in a rice canal between Houston and Galveston. Later, more populations were found at other sites.

In April 2001, Texas outlawed channeled applesnails as a harmful exotic species. The species is among 100 of the world’s worst invasive alien species, according to a list compiled by the Invasive Species Specialist Group in New Zealand.

As part of the survey, Dr. Lyubov Burlakova, an adjunct biology professor, and Dr. Alex Karatayev, associate professor at Stephen F. Austin State University in Nacogdoches, are surveying the distribution of snails in Harris, Galveston, Brazoria, Fort Bend, Waller, Chambers and Tarrant counties. Compiled data will be used to project the snail’s potential distribution.

In addition, biologists will study the snail’s seasonal population dynamics, including changes in density, size, structure, growth and reproduction rates as well as possible food items. Snail samples will be sent to Dr. Robert Cowie at the University of Hawaii to determine if more than one applesnail species exists in Texas.

Dr. Robert McMahon at the University of Texas in Arlington will also analyze the snail’s tolerance to water temperature, salinity, pH levels, and other factors that will help project areas most at risk for applesnail invasions.

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