Under towering palms and tangled mangroves, coil-shelled creatures slowly crawl across damp leaves and mossy rocks. As these invasive snails take advantage of the hot, wet ambiance of southern Florida, they leave glistening trails of slime across backyards, parks, forests, and gardens. The Sunshine State is a paradise for snails from other parts of the world who are being shipped in for the pet trade, outcompeting native species, spreading disease, and wreaking havoc overall.
“Florida has become a hotspot for invasive snails because of its tropical climate in the south end and enormous amount of freshwater springs for aquatic species,” says Lori Tolley-Jordan, an invertebrate zoologist at Jacksonville State University who specializes in freshwater invertebrate biodiversity. “While Alabama has the most diversity of [freshwater] snails, Florida’s environment and climate temperatures are very suitable for land and aquatic snails because it is not much different than their homes in southeast Asia and other tropical areas.”
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In turn, visitors like the giant African land snail from East Africa, one of the largest snails in the world, have found Florida to be a home away from home. As wide as the size of an adult hand with a unique brown lined shell, they make for a charismatic terrarium pet and are available for sale on websites like Amazon. That means they typically arrive through one of the 16 seaports in Florida that aid the multi-billion-dollar wildlife trafficking business. “It’s one of the largest ports of entry into the US,” Trolley-Jordan says.
Some time after an imported species like the giant African snail or potted apple snail arrives at its new home, the buyer may decide to release the snail into the wild, thinking it’s the humane thing to do. However, the critters become an issue with their ability to spread quickly and quietly, munching on essential plants and crops along the way.
“One of the [indicators] for species that are the most invasive, if anything, is their ability to reproduce quickly,” says Trolley-Jordan.
The giant African snail first came to Florida in the 1960s. It was forcibly wiped out from the state in the 1970s, but made a comeback through seaports in 2011. As the population expands its range, it has begun to impact the environment and the survivability of its native counterparts, including the Florida apple snail. With the ability to populate quickly, a hermaphroditic giant African snail or dioecious exotic apple snail can produce as many as 500 eggs every one to two weeks. Inversely, a native apple snail needs to find a mate to reproduce as little as 20 eggs per clutch every few weeks.
“There are several species of non-native snails in Florida, but most of them are locally restricted and have been confined in Florida for decades. So they only have gotten out by people having them as pets,” says Robert Fletcher, a professor in wildlife ecology at the University of Florida and principle investigator of a snail kite monitoring research team. “But, the [exotic apple snail] is a different story.”
A snail-sized apocalypse
As the alien snail species pump out numerous eggs, their sticky capsules become sneaky stowaways, clinging to unsuspecting humans and animals that whisk them away to new areas. Within weeks, the newly hatched babies will overwhelm their surroundings.
“Even if a person hasn’t released that species, that species can happen to be found on other plants when they are being sold or moved around that their eggs are attached to,” Trolley-Jordan says. “Either intentionally or unintentionally, they move everywhere.”
Already, shady exotic drifters like the trumpet snail and island apple snail have extended their ranges and colonized new ecosystems in multiple parts of the US. They also end up bringing extra company with them: parasites. Notorious for pathogens, species like the trumpet snail serve as vectors for the lung fluke, a flatworm that causes meningitis-like symptoms in humans and can sometimes be deadly to wildlife. Meanwhile, the giant African land snail carries roundworms, which can trigger intestinal issues.
The devastation wrought by these snails can be felt up the food chain, too. Non-native apple snails, for example, are outcompeting Florida apple snails, which are the primary food source for Everglade snail kites. This highly specialized bird of prey has been on the federal endangered species list since the 1960s, and has a relatively small population that is confined to southern Florida. The kite uses its unique hook-shaped beak to pry open snail shells, and has just started to crack into the larger invasive apple snails.
“There are lots of concerns about whether or not this non-native snail is going to further contribute to the decline of snail kites, and maybe push it to the brink of extinction,” says Fletcher. “[But] we have seen so far that this non-native highly invasive snail has essentially provided a Band-Aid for the snail kite.”
With the non-native apple snails increasing more rapidly than the native one, Fletcher says that his research team thinks it’s possible the invasive prey is “playing towards the increase in sort of the reversal of this population trend” in the snail kite—a glimmer of hope for the species.
As the battle for holding the balance between native and nonnative species in Florida continues, another slimy creature may soon enter this picture and add to the damage. “The assassin snail could wipe out entire populations of Florida’s unique spring snails if introduced,” says Tolley-Jordan.
The bumble bee-striped assassin snail doesn’t have an appetite for the plants in Florida like the apple snails, but will prey on smaller native species like Florida apple snails. It currently ranks as a top predator in its homeland of Malaysia, and will likely make its way to Singapore, a hotpot of global transport of invasive species, Trolley-Hordan notes. The zoologist has no doubt that it would thrive in the “Lion City” and New Zealand.
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As far as experts know, the assassin snail hasn’t entered Florida yet. But it’s a rising star on the pet market, so it might only be a matter of time.
Doing the detective work
One way scientists are able to determine if an invasive critter is getting too cozy in the Sunshine State is through environmental DNA or eDNA. For early detection, they can take water samples and look for traces of a specific species genetic material. The tool has been used in other parts of the US such as in the Mississippi River to detect black carp and the New Zealand mud snails.
Eradicating snail squatters can be tricky: Once they’ve spread through an ecosystem, they can be hard to find, catch and prevent from reproducing. This June, the Florida Department of Agriculture and Consumer Services began to treat in Broward County and other southern properties such as in Broward County for giant African snails with a pesticide called metaldehyde, a.k.a. snail bait. Once applied to crops and certain residential areas, the pesticide works by interfering with a snail’s ability to make mucus, ultimately impacting its mobility and digestion. Within days the target dies from dehydration. Officials also use specially trained canine units to sniff out the offenders.
Prevention through early detection, public outreach, and ecological management has proven to be the best strategy against the Sunshine State’s slimy epidemic. But of course, the best way to keep Florida from being taken over by alien snails is for pet owners to make smarter decisions, both for themselves and for the local wildlife and environment. “The public oftentimes is just not aware,” Trolley-Jordan says, “ It’s one of our biggest problems.”