Snakes pose threat to U.S. islands, officials respond

These are strange, dark days for the tiny tropical island of Guam. Thanks to an infestation of invasive snakes, this once-popular tourist destination is now bristling with the reptiles and, consequently, a boom in spider populations. But researchers have developed a brilliant solution to this shudder-inducing problem: lace dead mice with poison, strap them into parachutes, and drop them at the snakes’ front door.

Guam, a U.S. territory, sits in the Pacific Ocean east of the Philippines and north of Papua New Guinea. The tiny island covers only 209 square miles, a smaller area than the city of Chicago. And crammed into this cozy space are brown tree snakes — about two million of them.

The snakes arrived on the island about 60 years ago. In those post-World War II days, military vessels plied the South Pacific waters, little knowing that reptilian stowaways used the ships to pass among islands unhindered. On other Pacific islands, natural predators keep the nocturnal, tree-dwelling brown snakes in check. But on Guam, where no such predators exist, brown tree snakes flourish unchecked.

The snakes pose a considerable nuisance to Guam’s 159,000 human inhabitants. Between three and ten feet long, the snakes can tangle with power lines and cause costly outages. Their nonlethal bites irritate residents and deter tourists.

Far and away, though, the snakes’ greatest threat is to Guam’s native flora and fauna.

Many of the island’s native bird and small mammal species have no defense mechanisms against the snakes’ predation. As a consequence, the brown tree snake has driven to extinction nine of Guam’s twelve bird species. The others have suffered tremendous losses, slashing the island’s bird populations to just a few hundred individuals.

Birds are vital to any ecosystem. They help pollinate flowers, disperse seeds, and control insect populations. Remove the birds, and watch the ecosystem begin to unravel. Marc Hall, a supervisory wildlife biologist on Guam’s Andersen Air Force Base, told NPR, “Research is showing that the loss of the birds may be impacting the ability of the natural ecosystem to sustain itself.”

For proof, look to the spiders. In the past, Guam’s birds exerted dual controls over populations of the banana spider by snacking on both the arachnids and the insects that form the spiders’ diet. With the birds gone, the spider population has exploded. University of Washington Haldre Rogers found that during the wet season, Guam forests host about 40 times more spider webs than neighboring islands.

Ecosystem health and tourist revenue both suffer while Guam’s forests teem with snakes and spiders. But perhaps the biggest danger lies in what the snakes might do next.

Scientists on Guam and Hawaii dread the day when brown tree snakes make their way to the Hawaiian island chain. Even though Hawaii sits 3,000 miles across the ocean from Guam, there’s a very real risk of the snakes slipping into airplane cargo holds or wheel wells and setting up shop in a fresh island paradise.

If the snakes invaded Hawaii, the island chain’s ecosystems and tourist economies could collapse even more disastrously than Guam’s. Birds and small mammals on Hawaii would be spectacularly vulnerable to the snakes’ predation. The U.S. Department of Agriculture (USDA) estimates that if the snakes sneak into Hawaii, economic destruction “from medical incidents, power outages, and decreases in tourism…would range from approximately $593 million to $2.14 billion annually.”

That’s a risk no one’s willing to take. So the ingenious folks at the U.S. government have dreamed up an attack strategy to slash Guam’s brown tree snake population. The plan: pump dead baby mice full of acetaminophen and hand-drop them from helicopters into the forest canopy. Little parachutes strapped onto each mouse will catch in the upper branches and dangle the mice enticingly in the snakes’ faces.

On other islands, these mouse bombs could be as ecologically destructive as the snakes. But on desperate Guam, they seem like the best available option.

The plan is fairly solid. Unlike many other snakes, the brown tree snake has no qualms about eating dead food. USDA research has confirmed that acetaminophen—the active ingredient in drugs like Tylenol—will be fatal to the snakes. The mouse parachutes are designed to snag in trees, so no ground-dwelling animals or insects will be exposed to the toxins. Elsewhere, arboreal birds might be vulnerable to the drug-laced mice. “One concern was that [Guam’s] crows may eat mice with the toxicant,” said William Pitt at the U.S. National Wildlife Research Center’s Hawaii Field Station. “However, there are no longer wild crows on Guam.”

The mouse mission, scheduled for April or May of 2013, will target Guam’s Andersen Air Force Base. The base provides the snakes’ best strategy for jumping ship to Hawaii. Even though no brown tree snakes have been spotted in the Hawaiian Islands for 17 years, the pressure to halt the snakes is very real. Daniel Vice, assistant state director of the USDA’s Wildlife Services in the Pacific told NPR that without the toxic mouse rain, “I think the possibility of the snakes getting to Hawaii is inevitable.”