The apple snail, an exotic pest causing problems for Louisiana and Texas rice and crawfish operations, likely became established as a result of aquarium owners dumping the large snails.
The pests pose a double threat — they have a big appetite for vegetation, according to specialists at Louisiana State University. They also clog crawfish trap openings and tunnel through rice levees.
A population of the snail has forced a farmer in Acadia Parish, Louisiana, to shut down his crawfish harvest on a 220-acre field. And Cliff Mock, an Alvin, Texas, rice farmer and crop consultant, says the snail “is becoming a problem. They bore through the levees,” he said during the recent National Conservation Systems Cotton and Rice Conference in Memphis.
Mock says the snails have not caused crop damage but have torn up levees.
Bruce Schultz, in a release from the LSU AgCenter, reports that the snail may feed on rice plants. He cites AgCenter fisheries agent Mark Shirley, who says the snails have been found in Bayou Vermilion for the past two to three years.
“We’ve been seeing more and more of them in the past few years,” Shirley said.
He says the snails eat the vegetation that crawfish use for food, and they could also eat rice plants.
LSU AgCenter rice specialist Dustin Harrell says populations increase rapidly. He suspects that the snails entered the Acadia Parish field when it was flooded with water from a bayou that flows into the Mermentau River. Flooding in 2016 probably pushed water out of the Mermentau where the snail has been found for several years. “Ever since then, they moved and multiplied quickly,” he said.
They have also been detected in St. Mary Parish, where they seemed to be controlling salvinia, an invasive plant species.
The Acadia Parish farmer was collecting six to 12 crates full of the snails each day of harvest, specialists say. The snails were blocking the crawfish traps and complicating harvest so much that the farmer chose to pull his traps out of the field in late January.
Control Options Limited
Control is complicated. No chemical is labeled by the U.S. Environmental Protection Agency to kill the pest in Louisiana. But Harrell plans to bring up the problem when he visits federal officials in Washington, D.C.
Jacoby Carter, a research ecologist with the U.S. Geological Survey in Lafayette, has been studying the snails and says a pesticide that would kill the snail would likely kill crawfish too.
Drowning egg masses, a pink cluster found a few inches out of the water, may be an option. Eggs hatch in 11 to 21 days.
Mock says he has no control plans in place.
Texas A&M AgriLife entomologist Mo Way, at the AgriLife Research and Extension Center in Beaumont, says the snails can be quite large, “the size of a tennis ball. They have created problems in Asia and South America.”
“They are not hurting us so far except on the levees, where they are beginning to be trouble,” says Mock.
Harrell says the snail may pose a threat to small rice plants, although drill-seeded rice with a delayed flood may not be as susceptible to damage.
Two birds that feed on apple snails, the limpkin and the snail kite, move as the snail’s range expands, Carter says.
He also says the snails can carry a fatal disease, rat lungworm, but it has only been found in snails near New Orleans.
The apple snail is an invasive species, so it is illegal to collect, sell or transport them.