Florida’s wetlands are quietly losing native species to an air-breathing, mud-burrowing invader most residents have never heard of
Florida’s Everglades is already famous for the species it shouldn’t have — Burmese pythons, lionfish, giant land snails. But a quieter invader has been spreading through the wetlands for nearly two decades, and most Floridians have never encountered its name.
The Asian swamp eel is nocturnal, spends much of its time buried in mud and vegetation, and can breathe air directly from the atmosphere. Researchers are now documenting what it’s been doing to native wildlife in southern Florida — and the scale of the ecological change is drawing serious attention.
Not an eel — and that distinction matters
Despite the name, the Asian swamp eel (Monopterus species complex) isn’t a true eel at all. It’s a fish native to eastern and southeastern Asia — eel-shaped, yes, but belonging to an entirely different biological lineage. That distinction matters because its physiology sets it apart from nearly every other fish competing for space in Florida’s waterways.
The most consequential trait is its ability to breathe air directly from the atmosphere, with no dependence on dissolved oxygen in water. That single adaptation opens doors — literally — that are closed to most other fish.
In the Everglades, water levels shift dramatically with the seasons. During dry periods, shallow wetlands shrink and native fish get trapped in dwindling pools. The Asian swamp eel sidesteps this problem entirely — burrowing into mud to wait out a drought, or traveling short distances overland to reach new water. Florida’s seasonal rhythms, which stress most aquatic species, barely register as an obstacle.
As a generalist predator, it eats fish, crayfish, and whatever other small aquatic organisms happen to be available. It isn’t selective.
From 1,500 to 5,800 square kilometers in five years
The species was first documented in the Florida Everglades in 2007. From that initial foothold, expansion has been steady and measurable.
Between 2007 and 2017, the population occupied roughly 1,500 square kilometers of southern Florida — already a substantial area. Then, between 2017 and 2022, the range nearly quadrupled, reaching approximately 5,800 square kilometers as the population pushed west and north.
Today, Asian swamp eels are confirmed in 14 Florida hydrologic units, including areas connected to Lake Okeechobee, Tampa Bay, and several central and west Florida watersheds. This is no longer a southern Everglades problem.
Scientists note that pinning down the exact population size is difficult — the eel’s nocturnal, mud-burrowing habits make counting individuals nearly impossible. What the data do confirm is that the species is established, reproducing, and spreading. In some parts of the Everglades, it has reached high abundance.
A 99% collapse: what the data actually show
The numbers from long-term Everglades monitoring are striking. A 26-year analysis found that Asian swamp eel presence was associated with a 99% reduction in populations of two native crayfish species. That’s not a modest decline — it’s near-elimination.
Fish populations tell a similar story. Golden topminnow and eastern mosquitofish fell by more than 50% in affected areas, while flagfish and marsh killifish dropped by more than 90%. The southern leopard frog has effectively disappeared from areas south of Interstate 75 where the eel is now established.
None of these are species that generate the public attention alligators or Florida panthers do. But they’re critical links in the Everglades food web — crayfish and small fish that feed larger wading birds, reptiles, and mammals. When their numbers collapse, the effects ripple upward through the entire ecosystem. Quietly, but consequentially.
Hunting an invisible predator with DNA
Finding an animal that hides in mud, moves at night, and leaves no obvious trace presents a serious logistical challenge. Researchers have turned to environmental DNA — eDNA — a technique that sidesteps the problem of physically locating the eel altogether.
Every animal sheds biological material into the surrounding water: skin cells, mucus, waste. Scientists collect water samples and analyze the genetic material those samples contain. If an Asian swamp eel has been present, its DNA signature shows up even if no one ever sees the animal itself. The approach functions as an early warning system, allowing managers to identify where the species may be spreading before it becomes entrenched — rather than waiting until a population is large enough to catch by conventional methods.
Once eDNA signals identify a hotspot, researchers follow up with trapping and electrofishing, a method that temporarily stuns fish so biologists can capture and study them without lasting harm. This combination of non-invasive detection and targeted removal represents a more responsive management strategy than anything previously available for this species.
What ordinary Floridians can do right now
You don’t need a biology degree or a research vessel to contribute meaningfully to this effort.
The single most important preventive action is straightforward: never release non-native animals into Florida waterways. If you have an exotic fish or other pet you can no longer care for, Florida’s Exotic Pet Amnesty Program offers a legal, responsible alternative to releasing it into the wild.
Spotted something unusual while fishing, boating, or exploring Florida’s water systems? Report it. Sightings can be submitted through IveGot1.org, the IveGot1 mobile app, or by calling 1-888-IVEGOT1. It takes less than a minute, and early public reports directly support scientists’ ability to map the spread and respond before populations grow too large to manage.
The eDNA detection system is powerful, but it can’t be everywhere at once. Citizen observations fill in the gaps. As surveillance expands and trapping methods improve, the next few years will be telling — watch for whether the eel’s range continues pushing north, and whether early-detection efforts manage to slow it. The tools exist. The question is whether they’ll be deployed fast enough.
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