Burmese pythons have caused the most severe decline of native mammals ever documented in the Everglades, with populations of medium-sized mammals dropping by more than 90% in areas where pythons have become established. Since arriving in South Florida roughly 40 years ago, likely through escaped or released pets, these snakes have reshaped the food web from the top down, and their effects continue to ripple outward in ways scientists are still tracking.
Catastrophic Mammal Declines
The numbers are staggering. Road surveys conducted across nearly 57,000 kilometers in Everglades National Park between 2003 and 2011 documented a 99.3% decrease in raccoon sightings, a 98.9% drop in opossums, a 94.1% decline in white-tailed deer, and an 87.5% reduction in bobcats. Marsh rabbits, cottontail rabbits, and foxes were not detected at all during that entire period. In practical terms, animals that were once a routine part of the Everglades landscape have effectively vanished from large stretches of the park.
These aren’t minor prey species. Raccoons, opossums, and rabbits play central roles in the Everglades food web as both predators and prey. Their near-total disappearance has left a gap that affects everything above and below them in the chain.
What Pythons Eat
Burmese pythons are generalist predators, meaning they eat whatever they can catch and swallow. In the Everglades, that includes mammals from mice to deer, at least 25 species of adult birds, bird eggs, and other reptiles. Their flexible diet is part of what makes them so destructive: they don’t depend on a single food source, so their population doesn’t crash when one prey species runs low. They simply switch to the next available animal.
The largest python ever recorded in Florida measured 19 feet long and was caught in Big Cypress National Preserve in 2023. The heaviest on record weighed 215 pounds. Adults of this size can take down surprisingly large prey, including alligators, though most of their diet consists of smaller mammals and birds.
Cascading Effects on the Food Web
When you remove 90% or more of the medium-sized mammals from an ecosystem, the consequences extend far beyond those species. Raccoons and opossums are important seed dispersers, scattering seeds from fruits they eat across the landscape. Without them, certain plant populations may shift, altering the composition of vegetation over time. These same animals also help control insect and small reptile populations, and their absence allows those prey species to increase unchecked.
Researchers at Virginia Tech have outlined how these losses could cascade into changes in vegetation structure, nutrient cycling, and the overall architecture of the food web. The full extent of these indirect effects is still unfolding, but the principle is straightforward: every species that disappears leaves a hole, and the ecosystem rearranges itself around that absence, often in unpredictable ways.
A New Parasite Threatening Native Snakes
Pythons didn’t just bring themselves to Florida. They also introduced a parasitic organism called Raillietiella orientalis, a lung parasite native to Southeast Asia. This parasite has jumped to native Florida snakes, where it causes serious illness and death. Confirmed cases include pygmy rattlesnakes, banded water snakes, and the federally threatened Eastern indigo snake.
Initially confined to South Florida, the parasite has spread rapidly northward and now occupies much of peninsular Florida. This means pythons are harming native snake species even in areas where the pythons themselves haven’t yet established breeding populations. For already vulnerable species like the Eastern indigo snake, this added pressure is a significant concern.
How Many Pythons Are in the Everglades
Nobody knows the exact number, and that’s part of the problem. Burmese pythons are extremely difficult to find. They spend much of their time hidden in dense vegetation, submerged in swamp water, or tucked into underground burrows. Their camouflage is remarkably effective in the Everglades landscape. The U.S. Geological Survey conservatively estimates tens of thousands of pythons currently live in the Greater Everglades region, and the population appears to be growing.
Breeding populations are concentrated in Everglades National Park and Big Cypress National Preserve in extreme southern Florida. Cold winter temperatures have so far limited their northward spread, but within their current range they have proven extraordinarily successful. A single female can lay 50 to 100 eggs per clutch, and with few natural predators in Florida, survival rates for young pythons are high enough to sustain rapid population growth.
Removal Efforts and Their Limits
Florida has invested heavily in python removal. The South Florida Water Management District runs a Python Elimination Program that pays hunters to find and remove pythons from public lands. The annual Florida Python Challenge draws hundreds of participants: more than 850 people joined the 2024 event, collectively removing nearly 200 pythons. State and federal agencies track a combined running total of removals that continues to climb.
The challenge is scale. Removing a few hundred or even a few thousand pythons per year from a population of tens of thousands, spread across millions of acres of difficult terrain, does not reduce the overall population. Most of the Everglades is inaccessible sawgrass marsh and mangrove forest where hunters simply cannot go. Detection rates in these habitats are extremely low. Current removal programs likely help protect specific high-value areas and gather data on python biology, but they are not reducing the population at a landscape level.
The Everglades ecosystem evolved without a large constricting snake as an apex predator. Burmese pythons filled a niche that didn’t previously exist, and native wildlife had no evolutionary experience with this kind of threat. The result is an ongoing, large-scale ecological disruption with no clear endpoint in sight.