10/05/2026
Four times a second, a helicopter flying over Guam fires a dead mouse into the jungle canopy. Each mouse is packed with 80 milligrams of acetaminophen, the active ingredient in Tylenol, attached to two squares of cardboard joined by a four-foot green paper streamer. The cardboard catches in the upper branches. The streamer holds it in place. A brown tree snake finds a dead mouse hanging in a tree, eats it, goes into a coma, and dies within 60 hours.
A single helicopter load of 3,600 mice can treat 75 acres in half an hour. In test zones, the airdrops reduced snake density by 80 to 90 percent within weeks.
The reason the United States government is dropping poisoned mice from helicopters onto a Pacific island is that everything else has failed to control the snake that broke Guam.
The brown tree snake arrived sometime after World War II, most likely in military cargo from Papua New Guinea. A single pregnant female may have been enough. The island had no native snakes and no ground-based predators of any kind. It had 12 species of native forest bird, none of which had ever encountered a nocturnal arboreal predator with heat-sensing pits and rear-mounted fangs.
The population reached an estimated 1 to 2 million on a 200-square-mile island, a density of up to 33 snakes per acre in some areas. Nine of the 12 native forest bird species went extinct. The Guam rail and the Guam kingfisher survive only in captive breeding programs. One in 10 emergency room visits on Guam involves a brown tree snake bite, typically on sleeping infants and small children who are bitten at night when the snakes enter houses through gaps and vents.
Then it went after the power grid. Between 1978 and 1997, brown tree snakes caused 1,658 electrical outages on Guam, an average of one every three days. A snake climbs a power pole the way it climbs a tree, stretches across the insulator between the pole and the wire, completes the circuit with its own body, and shorts out the transformer. The outages span entire sections of the island and last eight hours or more. The annual cost exceeds $4.5 million.
Guam Power Authority and the U.S. military installed snake barriers around substations and critical infrastructure. Researchers found the snakes could stretch across gaps in barrier fences wider than anyone had designed for, which forced engineers to rebuild the barriers and clear vegetation farther from the fence lines. Every modification produced a new problem the snake solved through climbing ability that exceeded whatever the engineers had assumed.
The acetaminophen discovery was the breakthrough. For reasons that are not fully understood, 80 milligrams of acetaminophen disrupts the oxygen-carrying capacity of the brown tree snake's hemoglobin. The snake suffocates from the inside. The dose is roughly a quarter of what a parent gives a child for a fever.
It kills the snake in about 60 hours. Dan Vice, assistant state director of USDA Wildlife Services for the Pacific Islands, described what made the delivery possible: unlike most snakes, brown tree snakes readily eat prey they did not kill themselves. That is the c***k in the brown tree snake's armor, Vice said.
The problem was how to get the mice into the canopy. The snakes live in the upper branches. Ground-based traps catch some but cannot reach the density needed to suppress a population of a million or more across an entire island. The USDA designed a helicopter-mounted dispenser that fires cartridges containing the baited mice at four per second.
Each mouse trails its cardboard-and-streamer parachute into the canopy. A helicopter covers 75 acres in 15 to 30 minutes. There are few species on Guam that might eat the bait before the snakes find it, USDA researcher Kathy Fagerstone noted, because the brown tree snakes have already eaten most of them.
The program has not eradicated the snake. Field personnel still remove roughly 7,000 per year using traps, hand capture, and toxicants. A 55-hectare conservation area in northern Guam is now enclosed by a snake-proof fence, the only place on the island where native birds have been reintroduced behind a barrier the snakes cannot cross. The fence exists because after 70 years, poisoned mice, snake barriers, detector dogs, and 7,000 removals per year have reduced the population but have not eliminated it.
Image is for illustration purposes only
Source: Fritts (2002), International Biodeterioration and Biodegradation / National Geographic / NPR / NBC News / Stars and Stripes / ScienceBlog / USDA Wildlife Services / Guam Power Authority / U.S. Fish and Wildlife Service.
