\u201cIn a sense, this is an even worse invader than the python. We\u2019re talking about a species that is fundamentally altering wetland production,\u201d says Dr. Nathan Dorn, an associate professor at Florida International University<\/a> who specializes in freshwater ecology and predator-prey interactions in the Everglades. \u201cDon\u2019t get me wrong. I think both of them are devastating predators. But we\u2019re talking about the same level of concern.\u201d<\/p>\n Dr. Flaven Garcia, with the FIU Institute of Environment, holds up an Asian swamp eel in the Everglades. Photo by Anthory Mora \/ FIU Institute of Environment<\/p>\n These concerns have taken root over the last six to 10 years as swamp eels have expanded their range into the freshwater systems of the Everglades. They feed primarily on crayfish, as well as other, smaller forage fish that many native species rely on, too. Studies led by Dr. Dorn and other researchers have shown<\/a> that in some wetland areas where swamp eels are proliferating, crayfish populations have declined by 90 percent or more.<\/p>\n This is bad news for the species that eat crayfish \u2014 a long list that includes most wading birds and small mammals, along with alligators, turtles, bass, gar, and other gamefish. One 2025 study<\/a> that Dorn co-authored looked specifically at how this reduction in prey biomass has affected nesting wading birds, which are important indicators of ecological health.<\/p>\n \u201cThis is an observational data set, so you have to rule out all the other possible hypotheses on what\u2019s happening [with those crayfish populations],\u201d Dorn tells Outdoor Life. \u201cBut there really isn\u2019t a great explanation for these dramatic declines other than the invasion of this eel, which we know eats crayfish.\u201d<\/p>\n An Asian swamp eel in a tank at FIU. Photo by Dr. Brandon G\u00fcell \/ FIU Institute of Environment<\/p>\n Adding to these concerns are all the things biologists have yet to learn about Asian swamp eels, a grouping that includes multiple subspecies in the Synbranchidae<\/a> family. And unlike Burmese pythons, which live near water but can be tracked and hunted by humans<\/a> on dry land, Dorn says there are no established methods for controlling or eradicating swamp eels.<\/p>\n Beady-Eyed, Air-Breathing Hermaphrodites<\/p>\n We do know that Asian swamp eels<\/a> were first introduced to the freshwater canals around Miami in the late 1990s. A popular food source in countries like Indonesia and China, they were brought to Florida and other states as part of the live-food trade and were dumped into urban canals. From there, the eels moved south- and westward into the Everglades.<\/p>\n Dorn explains that by 2007, swamp eels were present in the far southern portions of the Everglades, and by 2012, they had spread into the larger rivers and drainages within the National Park. As of 2021, they\u2019ve moved northward into Broward and Palm Beach Counties, and the eels can now be found in most wetland environments throughout the region.<\/p>\n A map showing the spread of swamp eels in South Florida over time. Map by FIU<\/p>\n Part of the reason they\u2019ve adapted so well is because they evolved in the rice fields of Southeast Asia, where they\u2019re also called rice eels. They have what Dorn calls a modified breathing system \u201cthat is somewhere between a gill and a lung,\u201d which allows them to gulp air and breathe water. They can also burrow into the mud and sediment as water levels fall and lie dormant during droughts. One of the only ways researchers are finding the eels is through electro-fishing surveys.<\/p>\n \u201cHow far down they can go and what their tolerance is for drought is hard to tell,\u201d Dorn says. \u201cBut what is clear from our captures is that you can find them in a wetland that has gone dry, and they\u2019ll be there two months after it re-floods when there are basically no other fish present.\u201d<\/p>\n Dorn thinks this resilience amid drought is one of the reasons they\u2019ve had such devastating effects on crayfish populations. Unlike the native predators that are knocked back by drought, swamp eels are already lying in wait as water levels rise, prompting crayfish and other forage fish to repopulate the wetlands.<\/p>\n \u201cYou can see the effects of these animals establishing themselves. Because we had a long record of time where we had no eels in the system, and we can basically model and predict what crayfish densities should be given water depths today,\u201d Dorn says. \u201cSome of those same [crayfish] populations are down between 85 and 99 percent.\u201d<\/p>\n Asian swamp eels are novel hunters, too. Unlike an ibis or a largemouth bass, which mostly feeds during the day and uses its large eyes to hunt, swamp eels have tiny eyes and are more active at night.<\/p>\n \u201cThey appear to be ambush nocturnal predators, slowly slithering along the bottom or along vegetation until they detect something,\u201d Dorn explains. \u201cWe can\u2019t tell if [they\u2019re] using mechanoreception<\/a> or chemical reception or even electro-reception to identify prey. But it appears that they\u2019ll get within 10 centimeters and then just suck [the prey] right in.<\/p>\n Asian swamp eels are novel predators that can burrow into the mud and lay dormant until water levels rise. Photo by Anthory Mora \/ FIU Institute of Environment<\/p>\n \u201cSo, this is a very different kind of predator,\u201d Dorn continues. \u201cAnd for small animals in the Everglades, I don\u2019t even know exactly what the correct response would be \u2026 or what kind of prey traits would allow them to coexist with this animal. We\u2019ve puzzled over that one.\u201d<\/p>\n As if the beady-eyed eels were strange enough, they are also sequential hermaphrodites<\/a>. That means all swamp eels are born females, and some become males.<\/p>\n An Unchecked Invasion with No Control in Sight<\/p>\n The biggest Asian swamp eels can stretch up to three feet long, making it harder for other critters to feed on them. Dorn says bigger birds like blue herons will eat them, as will alligators and larger fish. But it\u2019s not enough to make a noticeable dent in their populations.<\/p>\n \u201cIn terms of natural control, I don\u2019t think we\u2019re seeing anything like that yet,\u201d Dorn says. \u201cTheir abundances are either flat in some of these wetlands where they\u2019ve been present for years, or they\u2019re still growing. And when I say they\u2019re abundances are flat, I mean they\u2019re still dominating the assemblages of larger fishes.\u201d<\/p>\n A great egret tries to eat a swamp eel. MMS*BanyanRanchStudios_7DMarkII<\/p>\n As for humans controlling their populations, we still have more to learn about swamp eels before we can figure out how to remove them. And with so many other invasives<\/a> now eating their way through the Everglades \u2014 species like Burmese pythons<\/a>, Nile monitors<\/a>, green iguanas, and cane toads \u2014 federal and state wildlife managers haven\u2019t always paid enough attention to the impacts that Asian swamp eels are having. Dorn says that in some cases, they\u2019ve also underestimated the eels, which have smaller mouths and seem less threatening than a 200-pound python that can swallow a deer whole<\/a>.<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/03\/5a4c28176a9bfd3819fb3333db057b44.jpeg\"\/)
<\/p>\n![\"An](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/03\/3b3e282d76a0192334f168a0692f2413.jpeg\"\/)
<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/03\/c73dc02c76f47fb4fc5ac760173eabcf.jpeg\"\/)
<\/p>\n![\"An](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/03\/abfed69a6d253c2a17a40c49bb0e407a.jpeg\"\/)
<\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/03\/ab2a9677f823d74fed6a4e99922cf961.jpeg\"\/)
<\/p>\n