GAINESVILLE, Florida, October 15, 2009 (ENS – Five giant exotic snake species already in the United States would pose high risks to the health of U.S. ecosystems if they become established here, according to a new U.S. Geological Survey report.

The USGS report details the risks of nine non-native boa, anaconda and python species that are invasive or potentially invasive in the United States. Because all nine species share characteristics associated with greater risks, none was found to be a low ecological risk.

Three of these species are documented as reproducing in the wild in South Florida, with population estimates for Burmese pythons in the tens of thousands.

Boa constrictors and northern African pythons already live wild in the Miami metropolitan area.

“This report clearly reveals that these giant snakes threaten to destabilize some of our most precious ecosystems and parks, primarily through predation on vulnerable native species,” said Dr. Robert Reed, a coauthor of the report and a USGS invasive species scientist and herpetologist.

In the last 30 years, over one million of these snakes have been imported into the United States for sale as pets, the report states, citing records kept under the Convention on International Trade in Endangered Species.

High-risk species – 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 but still potentially serious threats, say the authors.

Some species of the giant constrictors may also pose a small risk to people, although the USGS scientists say most snakes would not be large enough to consider a person as suitable prey.

Researchers implant a radio transmitter in a 16-foot, 155-pound female Burmese python at the South Florida Research Center, Everglades National Park. (Photo courtesy USGS)

Mature individuals of the largest species – Burmese, reticulated, and northern and southern African pythons – have been documented as attacking and killing people in the wild in their native range, though such unprovoked attacks appear to be quite rare.

The snake most associated with unprovoked human fatalities in the wild is the reticulated python. The situation with human risk is similar to that experienced with alligators, the repot says, “attacks in the wild are improbable but possible.”

Breeding populations have been confirmed in South Florida for Burmese pythons and boa constrictors, and there is strong evidence that the northern African python may have a breeding population in the wild as well, finds the report.

The authors emphasize that native American birds, mammals, and reptiles in areas of potential invasion have never had to deal with huge predatory snakes before. Individuals of the largest three species reach lengths of more than 20 feet and upwards of 200 pounds.

The reticulated python is the world’s longest snake, and the green anaconda is the heaviest snake. Both species have been found in the wild in South Florida, although breeding populations are not yet confirmed for either.

“Compounding their risk to native species and ecosystems is that these snakes mature early, produce large numbers of offspring, travel long distances, and have broad diets that allow them to eat most native birds and mammals,” said Dr. Gordon Rodda, a USGS scientist at the Fort Collins Science Center and the other coauthor of the report.

In addition, he said, most of these snakes can inhabit a variety of habitats and are quite tolerant of urban or suburban areas.

Reticulated pythons can grow up to 20 feet long. (Photo by Mariluna)

The report notes that there are no control tools yet that seem adequate for eradicating an established population of giant snakes once they have spread over a large area. Making the task of eradication more difficult is that in the wild these snakes are extremely difficult to find since their camouflaged coloration enables them to blend in well with their surroundings.

“We have a cautionary tale with the American island of Guam and the brown treesnake,” said Reed. “Within 40 years of its arrival, this invasive snake has decimated the island’s native wildlife – 10 of Guam’s 12 native forest birds, one of its two bat species, and about half of its native lizards are gone. The python introduction to Florida is so recent that the tally of ecological damage cannot yet be made.”

USGS researchers used the best available science to forecast areas of the country most at risk of invasion by these giant snakes. Based on climate alone, many of the species would be limited to the warmest areas of the United States, including parts of Florida, extreme south Texas, Hawaii, and America’s tropical islands, such as Puerto Rico, Guam, and other Pacific islands.

For a few species, such as the Burmese python, climatic conditions across much of the southern United States are suitable. The Burmese python is exceptional in its ability to tolerate cold weather through hibernation, the authors say. Most of the other species are likely limited to areas where below-freezing weather is short-term and can be avoided by submergence in shallow burrows or water.

The Fish and Wildlife Service and the National Park Service will use the report to develop management actions to control the snakes when they appear in the wild.

At present, the only probable pathway by which these species would become established in the United States is the pet trade, the report concludes. “Importation for the pet trade entails a risk of establishment of these animals as exotic or invasive species, but it hardly guarantees that establishment,” the authors state. “Federal regulators have the task of appraising the importation risks and balancing those risks against economic, social, and ecological benefits associated with the importation.”

Click here to view the report, “Giant Constrictors: Biological and Management Profiles and an Establishment Risk Assessment for Nine Large Species of Pythons, Anacondas, and the Boa Constrictor.”

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