Battling the brown tree snake in Guam

Getting rid of the snakes is going to be anenormous job for the US government

The US territory of Guam, an island in the western Pacific, is only 50km (30 miles) long and 10km wide, but it is packed with two million snakes.

This reptile arrived here only 60 years ago but has rapidly become one of the most successful invasive species ever.

Wildlife biologist James Stanford, from the US Geological Survey, says: "Our belief is that they came at the end of World War II.

"We've looked at their genetics and they are all extremely closely related, and it appears they came from the Island of Manus in Papua New Guinea."

He explains that military equipment used by the US in Papua New Guinea while the war raged in the Pacific was eventually sent back to Guam to be processed. A snake probably crept on to a ship or a plane destined for the island.


Cheryl Calaustro says the koko was easy prey for the snakes
"And from that handful, or maybe even one already impregnated female, we now have a population that is unbelievable in scale," he says.

The snakes, which are mildly venomous, have caused many problems. They get everywhere, and people have even woken up with them in their beds.

The island's power system is regularly shorted out by snakes crawling on the lines. It is so frequent the locals now call power cuts "brown outs".

But the biggest impact has been on the wildlife - it has been decimated. The forests here are eerily quiet. Now the only place where the Guam's native birds, such as the koko, can be seen on the island are in cages in a captive breeding centre.

"The brown tree snake has had a devastating impact. Ten out of 12 native forest bird species disappeared in 30 years," says Cheryl Calaustro from Guam's Department of Agriculture.

"The birds here evolved without predators. They were quite naive. And when the snake arrived on Guam it ate eggs, juveniles, adults. Whole generations disappeared."

Toxic mouse bombs

But the snakes did not stop there.

Dr Stanford explains: "We thought it would be limited: 'OK, if it wipes out the birds, it will decline.' It wasn't the case. It just switched what it was feeding on - rodents, lizards, small mammals - across the board."

Now the locals are fighting back. And they are unleashing some unusual weapons in their war against the snake.

One effort has involved air-dropping mice that have been laced with poison and fitted with parachutes out of helicopters. It provides a deadly dinner for any unsuspecting snakes below.

"Right now we are using acetaminophen (paracetamol). It commonly used as a pain reliever and fever reducer in humans, but it is 100% lethal to all brown tree snakes," explains Dan Vice of the US Department of Agriculture.

"If they eat that dead mouse containing acetaminophen, they will die."   (BBC.co.uk)