In the fall of 2019, Dr. Melissa Faroh, a herpetologist, was performing a necropsy on a dead eastern indigo snake recovered from a wildlife corridor in Kier County, Florida. Inside its lungs, she found dozens of small, segmented worm-like parasites. Faroh had conducted hundreds of these procedures and recognized a parasitic infection, but she did not recognize the parasite itself. It was not a species documented in North American snakes before.
Tissue samples sent for identification returned a result that seemed inconsistent with the animal’s history. The parasite was native to Asia and Africa and had no known presence in the lungs of North American snakes. The snake had never left Florida. The parasite was identified as Raillietella orientalis, a pentastome commonly called a tongue worm. Pentastomes are an ancient lineage of parasitic arthropods, distantly related to crustaceans, that live inside the respiratory tracts of reptiles.
The presence of this parasite in a Florida native snake raised a broader question about what else arrived with the Burmese python population. The python’s establishment in the Florida Everglades is a well-documented story. The species entered the United States through the exotic pet trade starting in the 1970s, with tens of thousands of individuals imported before their full adult size was widely understood. Some escaped, others were released, and Hurricane Andrew’s destruction of breeding facilities in 1992 accelerated an establishment that was likely already underway.
By the time biologists confirmed wild breeding, the pythons had spread across more than a thousand square miles of South Florida. Mammal populations in the hardest-hit areas saw dramatic declines, with raccoon and opossum sightings down by more than 90 percent. That impact is frequently discussed. Less discussed is what the pythons carried with them.
Raillietella orientalis evolved alongside Burmese pythons in Southeast Asia, where the relationship had reached a rough evolutionary balance. A wild python carrying a light or moderate worm burden typically shows few outward signs of illness. In Florida, however, the parasite found a new environment. Surveys of wild-caught pythons in South Florida found infection rates in some populations exceeding 70 percent, with more than 100 adult parasites recovered from a single set of lungs in the heaviest infected individuals.
The parasite then began appearing in native snakes that had no evolutionary history with it. Since the first confirmed native infection, Raillietella orientalis has been documented in at least a dozen native Florida snake species, including water snakes, black racers, cottonmouths, and several rat snake species. Its spread has reached parts of the state beyond the python’s core range.
The parasite does not require direct contact between a python and a native snake to spread. Its life cycle typically runs through an intermediate host, likely small reptiles, amphibians, or arthropods that both pythons and native snakes prey on. Researchers screening potential intermediate hosts have found parasite larvae in several common lizard and frog species. This means the infection can move through a shared food web faster and further than the python population expanding on its own.
In native hosts, the relationship looks different from the manageable balance seen in pythons. Researchers at the University of Florida found that native snakes infected with Raillietella orientalis carried heavier parasite loads on average than the pythons the parasite originally arrived with. Individual worms recovered from native snakes grew larger than those found in python lungs. Tissue damage, including inflammation, lung scarring, and airway obstruction, was consistently more severe in native snakes, even when pythons carried comparable total parasite counts.
The proposed explanation centers on evolutionary mismatch. Burmese pythons developed defenses against this specific parasite over a long shared history. Native Florida snakes have no such calibration. Their immune systems are responding to an unfamiliar organism, and in several documented cases, that response appears to damage the host’s own lung tissue more than the parasite’s physical presence alone.
For most native species, the ecological consequence is difficult to quantify against generally healthy, stable populations. Species like black racers and water snakes are common and widespread, and while a heavy infection is a welfare concern and a likely contributor to individual mortality, they are not at immediate extinction risk. The eastern indigo snake is different.
The eastern indigo is the longest native snake in North America, capable of exceeding two and a half meters. It has been federally listed as threatened since 1978. Its range has already been reduced by habitat loss, road mortality, and the destruction of gopher tortoise burrows. Indigo snakes are also one of the species documented preying directly on juvenile Burmese pythons, a behavior researchers have viewed as a limited point of ecological hope.
That behavior now looks more complicated. An indigo snake that preys on python hatchlings is also one of the native species most likely to be exposed to Raillietella orientalis, either through direct consumption of an infected python or through shared intermediate hosts. Confirmed infections in wild eastern indigo snakes have been linked to respiratory illness and, in some documented cases, mortality. The total wild population of the species is estimated in the low thousands across its entire range.
Researchers studying indigo snake recovery efforts now factor in a parasite risk that did not exist as a variable a decade ago. The parasite arrived as an unplanned side effect of an unrelated invasive species crisis.
This pattern is not unique to Florida. Wildlife biologists point to comparable cases elsewhere, including crayfish introducing a fungal plague to native crayfish and invasive amphibians introducing chytrid fungus strains into naive frog populations. In several of those cases, the parasite or pathogen mattered more for long-term native population decline than direct competition or predation from the invasive species itself.
Florida wildlife agencies and university teams have started monitoring for the parasite as part of broader native snake health surveys. There is no meaningful treatment or control program for a respiratory parasite spreading through a wild reptile population across an area the size of South Florida. Antiparasitic treatment exists and works in captive settings, but it does not scale to a wild population spread across thousands of square miles. Removing infected pythons through existing control programs may modestly reduce the parasite’s overall reservoir, but with infection established in a dozen or more native species and spreading through shared prey, culling the original host does little to slow a transmission chain that no longer depends on the python population.
There is also a geographic overlap. Much of the remaining eastern indigo snake range in Florida overlaps with core Burmese python territory. The conservation land set aside for the indigo snake’s recovery is often the same land where python density and parasite exposure risk run highest.
The documented predation by native species on pythons remains real. Bobcats raiding nests, cottonmouths and king snakes taking hatchlings, and alligators and indigo snakes accounting for a share of juvenile mortality are all documented. That predation represents a wild ecosystem responding to the invasion in ways that human control programs have not achieved. But the parasite finding complicates any straightforwardly hopeful reading. The same predation that represents a sign of native ecological resistance may also be spreading a disease risk into the most vulnerable native species.
Researchers are careful not to overstate what is known. Infection surveys remain limited in scope, and population-level mortality data for wild indigo snakes specifically attributable to pentastome infection is still sparse. Native populations could develop some degree of tolerance over a longer timeline, but that would likely take many generations, running against a python population that continues to expand.
The situation remains unresolved. The predation that represents the most promising sign of native ecological resistance in the python invasion may also be the mechanism spreading a respiratory parasite into a federally threatened species. Nobody planned for a parasite from Southeast Asia to end up in the lungs of one of North America’s rarest snakes. Nobody funded a study anticipating that outcome. It is happening quietly inside animals nobody is checking, spreading through a food web that connects the invader to the native species working hardest to resist it. Whether that becomes a footnote in an otherwise encouraging story or the reason the encouraging story stops being one is not a question anyone currently studying it is prepared to answer with confidence.
