In 1988, The Blob invaded Louisiana. The star of the remake of the 1958 film of the same name was a big, slimy, snotty alien thing.
It came from outer space.
In 2014, Louisiana finds itself invaded by another slimy, snotty alien — the largest freshwater snail on earth, the apple snail.
Like the original Blob, the apple snail eats anything — any animal (including other snails) slow enough for the apple snail to catch and any plant in the water.
When it has eaten all the plants in the water, it will crawl out of the water to eat nearby land plants. And it lays, of all things, clusters of hot-pink eggs on anything protruding from the water: tree limbs, wharf pilings and plants too tough to eat.
Our star here has the scientific name of Pomacea maculata. The first word in the name is based on the Latin word for “apple,” appropriate for the creature whose round shell grows to 6 inches in diameter. “Maculata” is Latin for “spot,” and refers to the spots that often occur inside their shells.
Four closely related species of apple snails occur in the world, all of them turning up in the aquarium trade at some time or another.
The species that has invaded south Louisiana is the channeled apple snail, also called the giant apple snail. It is native to Argentina, Uruguay and Brazil.
Its relative, the golden apple snail that is native to Argentina and Uruguay, is listed as one of the world’s 100 worst invasive species. It was introduced into Taiwan around 1980 to start an escargot industry to provide protein to farmers who lived primarily on a low-protein rice diet.
It didn’t catch on as a food item, and the snail rapidly spread to mainland China (where it is eaten), Indonesia, Thailand, Cambodia, Hong Kong, Japan, the Philippines and finally Hawaii.
Wherever it appeared, it became destructive to rice crops and, in Hawaii, the taro crop.
In the U.S. mainland, the presence of the golden apple snail has been confirmed in Florida, California and Arizona.
The third species, the spike-topped apple snail is also a South American native, being widespread throughout the Amazon River basin. While it has established populations in southern Florida, it is not considered a seriously invasive pest.
This species is primarily an algae grazer, and is therefore popular with aquarium keepers who usually refer to them as “mystery snails.”
Unfortunately, separating the four species is very difficult when they are young, and often the more-pestiferous species enter the aquarium trade.
Neither the golden apple snail nor especially the giant apple snail do a good job of keeping aquarium glass clean of algae. As a result some aquarists dump their “pets” in local waterways rather than destroying them.
The fourth species is the Florida apple snail, native to southern and Central Florida, and the islands of Cuba and Hispaniola. It finds its way into the aquarium trade, as well, but is not considered an invasive pest.
The giant apple snail, about which the rest of this discussion will be confined, is now common in many South Louisiana waterways, especially canals. Its presence is usually first noticed when the masses of hot-pink eggs lays appear on anything that sticks out of the water.
They are built to be survivors. On the right side of its body it has a gill-like breathing system for breathing underwater. The left side of the body holds a lung to breath atmospheric air. It will leave the water to feed if necessary.
In poorly oxygenated water, it uses a siphon to draw air into its lung while remaining submerged to avoid bird predators.
The purpose of laying its eggs above the water (which it does at night) seems to be to avoid egg predators in the water.
The giant apple snail is prolific, producing egg clutches of 2,000 eggs, as compared to 250 for the channeled apple snail or 20 to 30 for the Florida apple snail.
Researchers speculate that the compounds that produce the pink color (which fades as hatching nears) serve to make the eggs less edible and serve as anti-oxidants. Females can lay a clutch of eggs every seven to 10 days.
They can tolerate a wide variety of pHs and salinities as high as 10 parts per thousand (full-strength sea water is 35 ppt). The lower temperature limit is usually given as 50 degrees Fahrenheit, but the snail obviously survives lower temperatures than that in Louisiana.
It is thought that the snails burrow in the mud and go dormant in cold water. They have survived water temperatures as high as 138 degrees in laboratories.
Apple snails can survive long periods out of the water, protecting themselves from drying out by closing the opening of the shell with their operculum, a fingernail-like trap door mounted on the rear of their feet. At temperatures of 68 to 77 degrees and high humidity, they have survived up to 308 days in lab experiments. Life span is estimated to be as long as eight years.
The big snails are vigorous feeders, and eat a wide variety of water plants. Interestingly, they seem to prefer North American plants over South American plants from their native range, if given a choice.
Plants such as duckweed, an especially preferred plant, are eaten in one piece. Water hyacinths, on the other hand, are eaten much more slowly, and the roots are eaten before the leaves.
Giant apple snail shells come in a wide variety of colors, from pale olive green to dark green and include bands of brown, black and yellowish-tan. Both albino and golden color variations exist.
Few animals eat apple snails. In Florida, the snail kite — a hawk evolved to feed on the native Florida apple snail — will eat the other species, as well. The most-effective native Louisiana fish predator is the red-eared sunfish (aka chinquapin or lake runner), but its small mouth limits it to consuming juvenile snails.
Red-eared turtles (mobilians) have been observed feeding on giant apple snail eggs. However, the most-effective egg predators may be fire ants, to which snail clutches are susceptible because they are laid out of water.
Some researchers hold out hope that humans can become the best predator of apple snails, in spite of their poor track record so far as escargot. One biologist went so far as to suggest that the giant apple snail seems to thrive best in the same range as crawfish are cultured.
The reference is transparently to Louisiana, where South Louisianans are reputed to eat almost anything. By humorous coincidence, the John Folse Culinary Institute is housed in the same building as the biology department at Nicholls State University.
Displayed prominently on a one wall of the institute is a recipe titled “Attacking the Invader Gumbo.” It is for apple snails.
The recipe comes with a note of caution from NSU biology professor Dr. Gary LaFleur Jr. that apple snails must be thoroughly cooked because they can host rat lungworms, which can infect humans with nasty consequences.
