USDA drops Tylenol-laced dead mice by cardboard parachute to poison Guam's tree snakes

By 2013, Guam was 'awash' in one to two million brown tree snakes, all descended from a single pregnant stowaway that had slithered off a ship some sixty years earlier. With no natural predators, the snakes had eaten the island's forest birds to near-extinction — 'there are virtually no birds left in the forest', USDA biologist Dan Vice told NPR — and kept crawling into cargo, aircraft and ships, threatening other islands.

The countermeasure assembles three unobvious pieces. First, the bait: researchers had discovered that brown tree snakes on Guam readily eat dead prey — things they did not kill themselves — unlike most snakes. Second, the poison: acetaminophen, the common over-the-counter painkiller, chosen because it is highly toxic to the snakes while 'very low toxicity to virtually everything else'.

Third, the delivery: each dead mouse is affixed to a float made of two thin cardboard panels joined by accordion-folded tissue paper, so mice dropped from helicopters drift gently down into the treetops where the snakes live and feed. 'You could say that but it's not literally a parachute,' Vice said — 'we're trying to float them down gently.' Asked how such a scheme evolves, he answered: 'It's trying to solve a problem when you can't Google the solution. There's nobody that's done anything like this before.'

Dead mice laced with acetaminophen, hung under cardboard-and-tissue floats, dropped into the treetops where brown tree snakes eat prey they did not kill.

An aerial poison drop over a populated island rules out most toxins; acetaminophen's narrow toxicity profile made an otherwise reckless approach safe for everything except the snakes.

Most predators ignore carrion, so the target species had effectively monopolised the bait niche — dead mice reach brown tree snakes and almost nobody else.

Snakes live and hunt in the forest canopy, so the delivery system had to land bait above the ground, out of reach of non-target scavengers.

The whole design had no precedent to copy: the agency combined a field observation, a pharmaceutical property and improvised materials engineering into one program.

When you cannot attack a population directly, find the behaviour unique to the target — here, scavenging on carcasses — and attach your payload to it.

As of the December 2013 NPR report, the USDA and partner agencies were running the airdrops to suppress the snake population and protect remaining wildlife and cargo routes; the report gives no population outcome figures. Vice had worked on the Guam project for over a decade at that point, and the bait-parachute system remains the standard description of the island's snake-suppression program.