Apple snails: Slimy invader attacks La. crawfish and rice farms

Tristan Baurick
Fri, April 8, 2022

First it came for your wetlands. Now it’s coming for your crawfish and your rice.

A foreign snail that appeared in Louisiana just over 10 years ago and quickly infested ponds, bayous and streams in about 30 parishes has recently found its way to the farms that produce two of the state’s favorite foods.

The invasive apple snail has shut down harvest at some crawfish farms in Vermilion, Acadia and Jefferson Davis parishes and has made its first devastating appearance in rice fields. In March, the invasive mollusks wiped out a 50-acre field of rice, marking the first reported case of the snail damaging the crop in Louisiana.

"Where it’s hit ‘em, it’s hit ‘em hard,” said David Savoy, a Church Point crawfish farmer and chairman of the Louisiana Crawfish Promotion and Research Board. “In Vermilion, it’s so bad, you pick up a trap and there’s 5 to 10 pounds of them. It’s horrible.”




Attracted by the bait in traps, the snails crowd in, leaving little or no room for crawfish. At some farms, apple snails are being caught in such high numbers — sometimes 12 crates per day — that disposal of the thick-shelled snails is becoming a problem.

Some farmers have had to halt harvests and drain their ponds early, suffering revenue reductions of as much as 50%, said Blake Wilson, an LSU AgCenter researcher.

“The impact on some of those farms, particularly where snail populations have been building for years, has been immense,” he said.

Only about 10 crawfish farms have been affected, but new reports keep coming in.

Louisiana is by far the nation’s biggest crawfish producer. The industry contributes more than $300 million to the state economy each year and employs about 7,000 people, according to the research board.



“If the problem spreads to the whole industry, economic impacts could be tens of millions of dollars annually without effective control tactics,” Wilson said.

Those tactics are currently limited to pesticides. But what kills snails will also likely kill crawfish.

Native to South America, the apple snail’s first appearance in Louisiana was in a Gretna drainage canal in 2006.

They’re popular in the aquarium trade partly because they eat the algae that dirties tanks. But they get quite big — sometimes growing shells 6 inches in diameter — and they often have a strong, swampy odor. Their presence in the wild is likely due to aquarium owners dumping them in ditches and ponds.

The snails stay below the water's surface and aren’t often seen, but their bubblegum pink eggs are hard to miss. In clusters of 200 to 600, the tiny eggs have become an all-too-common sight on tree trucks and pilings just above the water line. Destroying the eggs is one of the best ways to reduce their numbers.



The state Department of Wildlife and Fisheries recommends people scrape the eggs off with a stick and crush them, or at least knock them into the water. Be careful not to touch them because the eggs contain a neurotoxin that can irritate skin and eyes.

The snails are edible but are known to carry rat lungworm, a parasite that can kill humans and other mammals.

Rapid reproducers and voracious eaters, the snail overpopulates waterways and kills off habitat important to native fish and other wildlife.

The snail’s appearance in crawfish farms comes at a particularly bad time for the industry. Crawfish have been hit with white spot syndrome, a deadly virus that was first discovered in farmed shrimp in Asia in the early 1990s and first appeared in Louisiana 2007.

The coronavirus pandemic has taken a toll as well. The AgCenter reported that some crawfish producers have been able to sell just 15% of their catch due to pandemic-related restaurant closures and occupancy limits.

Scientists and farmers are perplexed about how the snail arrived in crawfish farms and why certain farms are swarming with them.

“It’s weird,” AgCenter researcher Greg Lutz said. “It pops up in certain regions. You can have a farm with nothing, and three or four miles down the road they’re overrun.”

It could be that the snails benefit from flooding. An Acadia Parish farm started having a snail problem after its fields were flooded from a bayou linked to the Mermentau River, which is loaded with apple snails.

The snail has been identified in just one rice field so far, but the potential for widespread destruction is strong. It’s a major pest for rice growers in Spain, Asia and Central America. In the Philippines, the snail is considered a national menace, infesting about half the nation’s rice fields during the late 1980s.

The snail left almost nothing at the rice field near Rayne. Wilson estimated the field had two snails per square foot.

“There was no trace of rice,” he said. “If you didn’t know better, you’d think it was a snail production farm.”

The Courier
This article originally appeared on The Courier: Slimy invader attacks La. crawfish and rice farms