Another Reason to Worry About Burmese Pythons? This Parasite.

As scientists try to manage invasive Burmese pythons in Florida’s Everglades, an additional biological invasion—a python parasite—takes hold

By Stephenie Livingston
Wildlife Science
Sep 26, 2024

A Burmese python crosses a road near Miami. When University of Florida researchers examined 1,716 pythons in 2023, they found muskrats, deer, rabbits, wild boars, threatened birds, bobcats, 71 alligators, one goat and five domestic cats. And that was just in the snakes’ guts. Scientists also have found a worrying parasite in the pythons’ lungs. (Photo by Karine Aigner)

WHEN HURRICANE ANDREW ripped through South Florida on August 24, 1992, the Category 5 storm left thousands of zoo animals and escaped pets roaming loose in Miami, a longtime hub for imported exotic animals. Among those were hundreds of Burmese pythons, mostly fugitives of a destroyed reptile breeding facility.

A 19-foot python floated around in Biscayne Bay. Another was found dead on the beach. And one ate a family’s house cat as children watched in terror. It was hauled off with “a monstrous lump” in its abdomen.

While the hurricane revealed the python problem to the general public, the nonvenomous snakes likely had a foothold in the region long before the storm. People began releasing pythons, trendy in the 1970s and ’80s, into the wild after realizing a predator that can reach 20 feet long and 200 pounds makes a ridiculous pet. Fast-forward a few decades, and headlines about a python capture mean it’s just another day in Florida.

Over time, many of those pythons have taken up residence in the Everglades, a 5,000-year-old subtropical wetland system some 50 miles wide by 100 miles long—the largest habitat of its kind left in North America and the closest thing in South Florida to the pythons’ native marshes of Southeast Asia. Home to more than 1,400 native plant and animal species, the remote Everglades is also a hotbed of invasive species, from old-world climbing ferns that can engulf entire tree islands to giant African snails that wipe out small farms, leaving behind trails of foul-smelling excrement. In the Everglades, it’s easier to spot an invasive species than to eye a native alligator or Florida panther.

Except for Burmese pythons. Although plentiful in number, the snakes are masters of camouflage, blending into the murky fresh water and thick marsh grasses that also provide ample native wildlife for them to eat. “Detection is our biggest management obstacle,” says Michael Kirkland, lead invasive species biologist for the South Florida Water Management District (SFWMD). “Removing pythons is simple, but finding them is the hard part.”

As it turns out, another invasive species is also especially good at going unnoticed. Raillietiella orientalis, a lung parasite the pythons carry, may be even better at hiding than the snakes themselves. And they wreak a whole different kind of havoc.

An image of a Burmese python hiding in the grass.

A Burmese python takes cover in Everglades National Park.

So many snakes

Nobody knows how many Burmese pythons inhabit South Florida, but given that more than 18,000 have been captured in the state since the 1990s, the number conservatively runs in the tens of thousands. Pythons can live for more than 20 years, with each female producing a clutch of 50 to 100 eggs annually. With few predators, an unchecked population could continue to grow exponentially. In fact, before pythons invaded the Everglades, most state wildlife experts had no experience with snakes as apex predators.

That’s not to say the state hasn’t tried to curb the spread, with agencies tracking pythons by airboat, plane, kayak and foot. Florida Fish and Wildlife Conservation Commission (FWC) and SFWMD contract hunters to scour the Everglades and its levees for pythons. In 2017, the University of Florida (UF) employed snake hunters from India’s Irula tribe. Other scientists are collecting environmental DNA, or eDNA (see “Following the Trail of eDNA”), as a means of surveying potential habitats.

Even so, the python persists. “We’re never going to eradicate the python population at this stage of the game, unfortunately,” Kirkland says.

That’s not great for a lot of reasons—among them, the pythons’ role in the declines of native wildlife populations, from white-tailed deer to the endangered Key Largo woodrat to native snakes integral to Florida’s food webs. While slither-averse readers might shiver at the thought, native snakes help control rodent populations; their venom is used in pharmaceutical drugs and medical diagnostics; and they provide food for native mammals, other reptiles and birds.

Which makes a pathogen associated with the pythons all the more problematic.

An image of Melissa Miller and Brandon Welty tracking a python in the Florida Everglades.

University of Florida’s Melissa Miller and Brandon Welty use telemetry equipment to track the notoriously hard- to-find snakes through Everglades sawgrass in June.

What lies within

Proliferating under the radar while pythons take the spotlight is the stowaway pentastome parasite R. orientalis. Brought to Florida from Asia by Burmese pythons, it likely has existed in the state as long as its hosts. A group of common, wormlike parasites, pentastomes typically attack the respiratory systems of certain vertebrates, including humans. While pythons have evolved to deal with this particular bloodsucking species, less-inured hosts—such as Florida’s native black racers and pygmy rattlesnakes—may be rendered anemic and left struggling to breathe.

Melissa Miller, a self-described snake lover and UF wildlife ecologist, oversees the invasive species research program for the Croc Docs laboratory, specializing in South Florida and the Caribbean. In 2012, she found Florida’s first known wild native snake infected with R. orientalis: an eastern garter snake. Over the next few years, she confirmed the parasite had spilled from Burmese pythons to more than a dozen species of native snakes, as well as other reptiles and amphibians. In a 2020 study published in Ecosphere, she documented 1,083 R. orientalis pulled from the bodies of 523 native snakes.

As if that wasn’t enough, Miller found definitive evidence the parasite is no longer dependent on pythons, often using reptiles and amphibians—including invasive Argentine black and white tegus and tokay geckos—as intermediate hosts. While pythons require tropical climates, R. orientalis is more versatile. “It’s not held to the same kind of climactic or physiological restraints that may restrain a python from advancing northward,” she says. “It has the potential to spread pretty far.”

When she first sampled wild native snakes in Florida, Georgia and Alabama in the early 2010s, the parasite was only detected in South Florida. Within five years, it had appeared in two counties farther north. Since then, researchers have found examples of infected native snakes in various locations from south to north Florida, with four more impacted native snake species recently identified, bringing the current total to 18 of Florida’s 46 native snakes.

It’s unknown how deadly the parasite may be to native snakes and whether native species, like the threatened , might build resistance to infection over time. Miller and UF colleagues are collaborating with the U.S. Geological Survey (USGS) and the National Park Service to design ongoing controlled lab studies that will examine the impacts of R. orientalis on host fitness—something she says is needed “before we can definitively say the sky is falling.”

Even so, “based on what we know concerning altered host-parasite dynamics during biological invasions, this could be very bad for native wildlife,” she says.

An image of an adult female Raillietiella orientalis.

A macro photo (above) provides a detailed view of an adult female R. orientalis. Doctoral student Jenna Palmisano found a dead dusky pygmy rattlesnake (below), a native species susceptible to the invasive parasite, with two R. orientalis still alive in its mouth.

Taking up space

Snakes carry all sorts of parasites. Last year, doctors removed a 3-inch parasitic roundworm common in carpet pythons from the brain of an Australian woman while it was still alive and moving. Although some pentastomes cause severe illnesses in people, infections are rare. Miller says the likelihood of R. orientalis infecting humans is very low, but “you definitely don’t want to eat undercooked python meat,” referring to Florida recipes—python curry, southern fried python—that make use of the invasives. (Python hunting in 32 designated FWC areas does not require a permit in Florida, and it’s legal for hunters to keep the meat and skin.)

Jenna Palmisano, a doctoral student at the University of Central Florida who studies snake pathogens, says R. orientalis appears to have three life stages, each inside different hosts. The parasite’s eggs enter the environment via python feces. Next, cockroaches and other insects digest the egg-laden feces and become infected with the larvae. Freezing temperatures spell death, but the parasites can avoid that fate when lizards and frogs eat cockroaches and other insect hosts, allowing R. orientalis to stay warm inside amphibian bodies beneath the frost line all winter. (The Everglades only sees a hard freeze once a decade or so, but North Florida, where the parasite’s range has expanded, freezes most years.)

An image of a dead dusky pygmy rattlesnake with an invasive parasite.

When a native snake eats the amphibian, the parasite enters its final host. There, in the snake’s lungs, the parasite reaches sexual maturity, begins to expel eggs, and the life cycle begins again. Although males die not long after reproduction, it’s unknown how long the females survive and produce eggs. Past pentastome studies suggest R. orientalis may live for years inside their hosts.

“Those larvae bore—it’s super weird—but they bore directly into the lungs; they make a straight path to the lungs,” Palmisano says. “Snakes get really intense infections. Two weeks ago, I dissected a black racer that had 107 of these parasites, and they are large. They are really big.” Female R. orientalis grow larger than the males, reaching more than 4 inches long, “which is crazy,” Palmisano says, since some black racers grow to only 35 inches long.

R. orientalis evolved specifically for the Burmese python’s relatively spacious respiratory system. In the body of a 1- to 2-foot-long pygmy rattlesnake, however, a different experience unfolds. In these Florida natives—a species that controls populations of small amphibians and provides food for hawks and owls—severe symptoms can range from pulmonary inflammation and lesions to breathing problems, anemia, pneumonia and even sepsis.

For her research on pygmy rattlesnakes’ genetic susceptibility to R. orientalis, Palmisano samples wild native snakes from 13 sites in central Florida. She recently found four dead rattlers, including one with the parasite spilling out of its mouth, although she cautions that it’s hard to say for sure whether the snake’s death was directly caused by the parasite. To better understand how severely native snake populations could be affected, she founded Snake Lungworm Alliance and Monitoring (SLAM), a group of researchers and collaborators in the Southeast who collect native snakes and document where the parasite is found. (While “Snake lungworm” is a common nickname for R. orientalis, some scientists caution against its use, given that the parasite, which is closely related to crustaceans, isn’t a worm.)

“It’s scary, but in some way, it kind of lights a fire to keep going, because the only way to unravel the threat is to figure out what its actual impact is,” Palmisano says.

An image of an Argentine black and white tegu.

Invasive Argentine black and white tegus, such as the one above in a yard bordering Everglades National Park, can act as intermediate parasitic hosts. Outgrowing their dependence on pythons has led to R. orientalis’ range expanding north.

Scouting for the future

Burmese pythons are an incubator of sorts. Besides pentastomes, they also carry Nidovirales viruses. This order, which includes coronaviruses, is known for its ability to jump to new hosts. Nonnative pythons can even contract native Florida pathogens—pathogens that, in theory, could mutate within python host bodies into something new. To uncover emerging pathogens and new mutations, scientists need python specimens.

But gathering snakes in a vast and remote wilderness like the Everglades isn’t easy. In some areas, little to no data exist on python ecology, which is why Kirkland and Miller teamed up in 2022 to create a scout snake program in the Everglades’ 671,831-acre Francis S. Taylor Wildlife Management Area.

When the team captures a python, they implant a transmitter and release the snake, now called a scout, back into the wild. During the winter and spring breeding season, that scout snake can lead researchers to python mating orgies: “breeding balls” that weigh around 500 pounds and consist of several males lured by a female’s sex pheromones. Once the snakes are caught, they’re either euthanized and subjected to necropsy so researchers can study their diet, reproduction and pathogens, or they’re fitted with transmitters to join other scouts. Miller’s project, one of four in South Florida, currently tracks 14 individual pythons.

Data from scouting and removal efforts eventually could help scientists put a rough number on local python populations. By creating a baseline estimate, researchers might be able to say about removal efforts over time, “you’re driving the population down,” according to Amy Yackel Adams, a USGS research ecologist working with Miller.

Until researchers can begin to appraise the number of pythons in the Everglades, it’s tough to extrapolate how prevalent R. orientalis truly is—much less the scale of its potential danger to native snakes in the wetlands. Because the parasite is no longer dependent on pythons, controlling the python population won’t control the parasites, but continued study could help identify the most impacted areas. And because python-removal efforts revealed R. orientalis in the first place, future removal efforts could detect new pathogens.

Some see this collective work as a positive step. “I’m very hopeful and optimistic that we’re going to continue to perfect current management strategies to the point where the Everglades is once again a safe place for the native wildlife that we all revere,” Kirkland says.

In the meantime, the work provides valuable insights about python habitat and breeding behavior. One grad student in Miller’s lab, Brandon Welty, says the team captured eight Burmese pythons during the 2024 season. “I was surprised to see that all breeding aggregations and pairs were found in aquatic habitats,” says Welty, who found pythons mating on top of flattened cattails. Last year Miller’s team typically found breeding pythons on dry land. (In a drier area on the opposite side of the Everglades, researchers apprehended 26 pythons this season.)

As with pythons, unknowns also prevail for now when it comes to R. orientalis. Palmisano suggests that limiting the sale of wild-caught Florida snakes as pets—and taking steps to ensure those snakes are pathogen-free—could slow the parasite’s spread. (Capturing and selling wild snakes in Florida requires a permit.) If she had to guess, Palmisano says R. orientalis probably has spread outside of Florida to neighboring states, where SLAM collaborators are looking for it. She says it takes a while for a parasite to saturate an ecosystem to the point where it can be detected by chance.

Meanwhile, researchers continue their attempts to gauge the parasite’s impacts on native snakes. At one site in Florida where scientists have studied pygmy rattlesnakes since the 1990s, they used to find an average of 30 a day. You could hardly walk a trail without kicking a snake. Now they struggle to find one or two a day. Is R. orientalis to blame— or something else? Climate change, habitat loss and other maladies like snake fungal disease—another emerging pathogen that causes abnormal molting, cloudy eyes and death in some species—all threaten Florida’s native snakes.

“It’s not good, because those populations are already struggling with habitat loss and other stressors,” Adams says. “And this could be like the icing on the cake that puts the species at risk of disappearing.”

Read more about writer Stephenie Livingston.