Dead mice laced with painkillers are about to rain down on Guam’s jungle canopy. They are scientists’ prescription for a headache that has caused the tiny US territory misery for more than 60 years: the brown tree snake.
Most of Guam’s native bird species are extinct because of the snake, which reached the island’s thick jungles by hitching rides from the South Pacific on US military ships shortly after World War II. There may be 2 million of the reptiles on Guam now, decimating wildlife, biting residents and even knocking out electricity by slithering onto power lines.
More than 4,830km away, environmental officials in Hawaii have long feared a similar invasion — which in their case likely would be a “snakes on a plane” scenario. That would cost the state many vulnerable species and billions of dollars, but the risk will fall if Guam’s air-drop strategy succeeds.
“We are taking this to a new phase,” said Daniel Vice, assistant state director of the US Department of Agriculture’s Wildlife Services in Hawaii, Guam and the Pacific Islands. “There really is no other place in the world with a snake problem like Guam.”
Brown tree snakes are generally 1m long, but can grow to be more than 3m in length. Most of Guam’s native birds were defenseless against the nocturnal, tree-based predators, and within a few decades of the reptile’s arrival, nearly all of them were wiped out.
The snakes can also climb power poles and wires, causing blackouts, or slither into homes and bite people, including babies; they use venom on their prey, but it is not lethal to humans. The infestation and the toll it has taken on native wildlife have tarnished Guam’s image as a tourism haven, though the snakes are rarely seen outside their jungle habitat. The solution to this headache, fittingly enough, is acetaminophen, the active ingredient in painkillers including Tylenol.
The strategy takes advantage of the snake’s two big weaknesses. Unlike most snakes, brown tree snakes are happy to eat prey they did not kill themselves, and they are highly vulnerable to acetaminophen, which is harmless to humans.
The upcoming mice drop is targeted to hit snakes near Guam’s sprawling Andersen Air Force Base, which is surrounded by heavy foliage and if compromised would offer the snakes a potential ticket off the island. Using helicopters, the dead neonatal mice will be dropped by hand, one by one. US government scientists have been perfecting the mice-drop strategy for more than a decade with support from the US Department of Defense and the US Department of the Interior.
To keep the mice bait from dropping all the way to the ground, where it could be eaten by other animals or attract insects as they rot, researchers have developed a flotation device with streamers designed to catch in the branches of the forest foliage, where the snakes live and feed.
Experts say the impact on other species will be minimal, particularly since the snakes have themselves wiped out the birds that might have been most at risk.
“One concern was that crows may eat mice with the toxicant,” said William Pitt, of the US National Wildlife Research Center’s Hawaii Field Station. “However, there are no longer wild crows on Guam. We will continue to refine methods to increase efficiency and limit any potential non-target hazards.”