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Our Next Invasive Species Is a “Snail” of a Story

Have you ever heard of an apple snail? Unfortunately, it is not a “tasty-twist” on escargot, but rather an invasive species in Louisiana.

The first reported sighting of the apple snail was in 2006 and it has since grown into a pest for Louisiana crawfish farmers. In 2018, one Acadia Parish farm had to shut down its 220-acre crawfish pond due to the snails competing with crawfish for food.

Apple Snail Eggs

An apple snail egg mass.

Generally, crawfish ponds contain traps that allow farmers to catch the tasty crustaceans, however, “In isolated areas, apple snails become a nuisance to crawfish producers in ponds where snail populations are high,” said Mark Shirley, Louisiana Sea Grant (LSG) and LSU AgCenter Extension agent. “Large snails will prevent crawfish from entering a trap’s funnel entrance. I’ve seen one as big as a tennis ball, but they can become as large as a soft ball. Smaller ones get into the trap, which becomes a sorting mess for the crawfish farmer,” Shirley added. “Sometimes a farmer will collect sacks of snails rather than crawfish.”

In ideal conditions, female apple snails may weigh 6 ounces or more. In a marginal environment, females will weigh 3.5 ounces, said Jacoby Carter, Ph.D., a Wetland and Aquatic Research Center ecologist for U.S. Geological Survey. “Although male snails are smaller than their female counterparts, in a challenging habitat they can weigh at least 2.8 ounces,” said Carter.

A female apple snail can lay 5,000 or more eggs in an egg mass, with a hatching windows of 11 to 21 days. The egg mass’toxicity prevents predators from eating them. Hatchlings reach sexual maturity after two to three months.

Most apple snail eggs are identified by the bright pink egg mass that hang about 12-18 inches over bodies of water. This increases the probability that the hatchlings will land safely in the water and thrive.

Hand removal of apple snail eggs is the only approved method to control them in freshwater systems. Pesticides that can kill the snails are too dangerous to the environment. “Often times the snails will use a branch or even pieces of grass that hang above water to lay their eggs on,” Carter said. Crawfish farmers are advised to check their ponds
weekly for snails.

“These South American snails were originally located near and in the Amazonian River Basin,” stated Carter. In most cases, the snails were deemed undesirable to Louisiana aquarium owners. Subsequently, they were dumped into nearby waterways. The result, these slimy critters have navigated into crawfish ponds causing trouble that most hope
diminishes over time.