Drug-filled Mice Airdropped Over Guam to Kill Snakes

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A brown tree snake in Queensland, Australia (file photo).

Photograph by George Grall, National Geographic

Ker Than

for National Geographic News

Published September 24, 2010

Dead mice packed with drugs were recently airdropped into Guam’s dense jungle canopy—part of a new effort to kill an invasive species of snake on the U.S. Pacific island territory.

In the U.S. government-funded project, tablets of concentrated acetaminophen, the active ingredient in Tylenol, are placed in dead thumb-size mice, which are then used as bait for brown tree snakes.

In humans, acetaminophen helps soothe aches, pains, and fevers. But when ingested by brown tree snakes, the drug disrupts the oxygen-carrying ability of the snakes’ hemoglobin blood proteins.

“They go into a coma, and then death,” said Peter Savarie, a researcher with the U.S. Department of Agriculture (USDA) Wildlife Services, which has been developing the technique since 1995 through grants from the U.S. Departments of Defense and Interior.

Only about 80 milligrams of acetaminophen—equal to a child’s dose of Tylenol—are needed to kill an adult brown tree snake. Once ingested via a dead mouse, it typically takes about 60 hours for the drug to kill a snake.

“There are very few snakes that will consume something that they haven’t killed themselves,” added Dan Vice, assistant state director of USDA Wildlife Services in Hawaii, Guam, and the Pacific Islands.

But brown tree snakes will scavenge as well as hunt, he said, and that’s the “chink in the brown tree snake’s armor.”

Snakes Pests Decimated “Naïve” Wildlife

The brown tree snake is an arboreal species native to Australia, Papua New Guinea, and several Pacific islands. The snake preys on birds, lizards, bats, and small mammals.

Inadvertently introduced to Guam (map) from the Solomon Islands after World War II, brown tree snakes are responsible for the extinction or severe reduction of several of the island’s native species.

The brown tree snake “is a nocturnal, arboreal predator. There’s just nothing like it here. It arrived here and found an island full of very naïve native wildlife,” Vice said. (See

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The drop was only the second in the project’s history, and was done to help refine the technique before a larger field test is conducted in late 2010 or early 2011.

The drop was only the second in the project’s history, and was done to help refine the technique before a larger field test is conducted in late 2010 or early 2011.

A small subset of mice in the latest drop was equipped with radio transmitters, which the team will use to determine the baits’ efficiency.

A small subset of mice in the latest drop was equipped with radio transmitters, which the team will use to determine the baits’ efficiency.

” we out from bait has radio the If tomorrow go signal>”If we go out tomorrow and the radio signal from the bait has moved, it’s very likely that [it was eaten by] a snake,” Savarie said.

Wildlife Services collects the bodies of only the snakes that eat the mice that have radiocollars.

Wildlife Services collects the bodies of only the snakes that eat the mice that have radiocollars.

” eat We would find the other not that>”We would not find other snakes that would eat the bait,” said Kathy Fagerstone, Technology Transfer Program Manager for USDA Wildlife Services.

“>”However, the amount of acetaminophen in each mouse is small and would not present environmental hazards.”

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