Posted by: Michael Ritter PhD | October 17, 2009

Invasive “Giants”

An invasion is taking place in the United States, and the authorities are worried. It’s not an invasion by a foreign country but from a foreign country. I’m talking about an invasion of giant snakes. It’s not a “purposeful invasion”, at least from the snake’s point of view. That is, these snakes aren’t swimming the oceans to the shores of the United States. Humans are at the heart of this invasion.


Burmese Python (Courtesy USGS)

The problem started back in the 1990’s when some thought it cool to make pythons and boa constrictors imported from Southeast Asia household pets. One of the most popular, the Burmese python, can grow to 6 m (20 ft) and weigh as much as 113 kg (250 lb). Many who purchased the snakes soon found that these creatures require large spaces to live, have rather expensive food requirements, and can be dangerous. Without many agencies willing to accept them, disillusioned owners simply dumped them in the wild. A mistake, a big mistake. Florida estimates that there are over 100,000 large snakes slithering, not only through swampy wetlands, but increasingly turning up in suburban areas of South Florida.

The United States Geological Survey recently released the report, “Giant Constrictors: Profiles and an Establishment Risk Assessment for Nine Large Species of Pythons, Anacondas, and the Boa Constrictor.” Their conclusion was that high risk’ species like “Burmese pythons, northern and southern African pythons, boa constrictors and yellow anacondas—put larger portions of the U.S. mainland at risk, constitute a greater ecological threat, or are more common in trade and commerce. Medium-risk species—reticulated python, Deschauensee’s anaconda, green anaconda and Beni Anaconda—constitute lesser threats in these areas, but still are potentially serious threats.” 1 Breeding populations of Burmese python and boa constrictor have been confirmed in South Florida, and there is evidence that the northern African python is breeding in the wild as well. The world’s longest snake, the reticulated python reaching 8.7 m (28 feet) and the heaviest, the green anaconda, weighing 227 kg (550 pounds) have both been found in the wild of South Florida although breeding populations have not yet been confirmed.

These snakes possess several characteristics that make them a special threat to Florida ecosystems. They:

“1. Grow rapidly to a large size (some individuals of these species surpass 20 ft in length and 200 lbs in weight);
2. Are habitat generalists (they can live in many kinds of habitats and have behaviors that allow them to escape freezing temperatures);
3. Are dietary generalists (can eat a variety of mammals, bird, and reptiles);
4. Are arboreal (tree-living) when young, which puts birds and arboreal mammals such as squirrels and bats at risk and provide another avenue for quick dispersal of the snakes;
5. Are tolerant of urbanization (can live in urban/suburban areas);
6. Are well-concealed “sit-and-wait” predators (difficult to detect, difficult to trap due to infrequent movements between hiding places);
7. Mature rapidly and produce many offspring (females can store sperm and fertilize their eggs—which in some of these snakes can number more than 100—when conditions are favorable for bearing young);
8. Achieve high population densities (greater impact on native wildlife); and
9. Serve as potential hosts for parasites and diseases of economic and human health significance.” 2

Reticulated Python (Courtesy WikiCommons)

Reticulated Python (Courtesy WikiCommons)

Scientists are concerned that introduced constrictors have the potential to upset food webs by eliminating or depleting native species. Giant constrictors are capable of eating almost any kind of land-dwelling vertebrate or mammal. This is particularly problematic for species that are already endangered, most likely from habitat loss or competition from other introduced species. These snakes pose minimal risk to humans in the wild, only a few unprovoked attacks occur per year worldwide. Reticulated pythons are most associated with known unprovoked fatalities in the wild. Though rare, Burmese and African pythons are also known to attack. All known fatalities in the United States are from captive snakes, usually when the owner is interacting with it.2

Potential Range under Current Climate

Potential range under current climate (Courtesy USGS)

Potential Range by 2100 From Global Warming

Potential Range by 2100 from global warming (Courtesy USGS)

The Burmese Python is particularly troublesome because much of the southeastern United States has a similar climate to its natural habitat. In another study,  USGS mapped the potential range for this snake, and an alarming pattern was revealed. Though several factors such as type of food and suitable shelter play a role, the maps show where climate alone would not limit the python. Two maps were produced by the study, one showing the current areas where the climate is similar to that of the snake’s native ranges. The second projects the range based on “climate matches” from climate models near the end of the century. Climate changes brought on by global warming dramatically increases the range of the giant snakes.

Efforts are now underway to address the “invasion”.  Local and state ordinances are restricting ownership and requiring owner licensing and snake tagging. An eradication program is underway, but the snakes prolific breeding  in the wild is making it an extremely difficult task.

For more information about this growing problem, see:

References for this post:

  1. Report Documents the Risks of Giant Invasive Snakes in the U.S. (USGS)
  2. Giant Constrictor Risk Assessment: Frequently Asked Questions (USGS)
  3. USGS Maps Show Potential Non-Native Habitat Along Three U.S. Coasts
  4. Reticulated Python (WikiPedia)

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