Louisiana Rice: Invasive Snails Complicate Crawfish Harvest, Possible Threat to Rice

An apple snail from a crawfish pond near Rayne, Louisiana. Photo: Dustin Harrell, LSU Ag Center

An invasive species of snail has forced a farmer in Acadia Parish to shut down his crawfish harvest on a 220-acre field.

The pest, called the apple snail, clogs crawfish trap openings and complicates crawfish harvesting. It has a big appetite for vegetation. 

Dustin Harrell, LSU AgCenter rice specialist, said the farmer was collecting six to 12 crates full of the snails each day of harvest. The snails were blocking the crawfish traps and complicating the harvest so much that the farmer chose to pull his traps out of the field in late January.

Harrell said it’s suspected that the snails entered the field when it was flooded with water from a bayou that flows into the Mermentau River. He said 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.

Harrell said no chemical is labeled by the U.S. Environmental Protection Agency to kill the pest in Louisiana. He said he will bring up the problem next week when he visits federal officials in Washington, D.C.

Harrell said the snail poses a threat to small rice plants, although drill-seeded rice with a delayed flood may not be as susceptible to damage.

An egg mass of the apple snail on a drainage pipe in a crawfish pond. Photo: Dustin Harrell, LSU Ag Center

Mark Shirley, AgCenter fisheries agent, said 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,” he said.

Shirley said the snails eat the vegetation that crawfish use for food, and they could also eat rice plants.

Because they are an invasive species, it is illegal to collect, sell or transport them, he said.

Jacoby Carter, a research ecologist with the U.S. Geological Survey in Lafayette who has been studying the snails, said the mollusks can be controlled with a pesticide but it’s likely the compound would kill crawfish also. One means of control, said Carter, is to drown egg masses, which take 11 to 21 days to hatch. The pink cluster is usually seen a few inches out of the water.  According to Carter, the snails carry a fatal disease, rat lungworm, but it has only been found in snails near New Orleans.

The apple snails have been seen in St. Mary Parish where they seemed to be controlling salvinia, an invasive plant species. It’s suspected that aquarium owners got rid of the snails. “They’re not good for aquariums because they eat the vegetation,” said Carter.


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