How alien snakes left Guam infested with spiders

By Tierney Smith

In the 1940s a highly invasive species of snake – the brown treesnake – was accidentally introduced to the Pacific Island of Guam.

In just four decades, the snakes have wiped out 10 of 12 native bird species, killed various other animals that once roamed the island and caused a fortyfold increase in the Guam’s spider population.

“Most of the time you will probably never see [the snakes],” Cheryl Calaustro, a wildlife biologist at the Guam Department of Agriculture tells RTCC. “But when you go out into our forests you will notice a number of different things.

“You will not hear any birds, it is very silent, you will probably see and walk into many cobwebs because we do have a lot of spiders, because we do not have any birds to eat the insects and the spiders; and you will notice that our forests are somewhat monotypic, there’s one kind of tree.

“Those are all things that the snake has actually caused.”

Most people will only see a brown treesnake once or twice in their lifetime. They are nocturnal and hard to spot as their colour allows them to camouflage themselves. They can also move very fast.

But Calaustro says that there are between one and two million snakes on the island. Just 30 miles long and 7 miles wide, that amounts to around 12,000 snakes per acre.

And while you may not see the snakes themselves, residents of Guam will experience their impact.

“If you experience brown-outs or black-outs on Guam it could be because of the snake because they do climb very high,” says Calaustro. “If you have prey items in your back yard, like chickens or small puppies or kittens they will come into your yard and take those out.”

According to the International Union for the Conservation of Nature (IUCN) invasive species are the most significant cause of extinction worldwide after habitat destruction.

On islands, they are predominately the most significant cause.

The spread of these invasive, or alien species, increased dramatically as the world opened up in terms of trade, travel and the transportation of goods.

They often hitchhike on ships, in containers or in cars.

Calaustro warns that this problem must be tackled quickly after the introduction of a new species, to ensure the experience of Guam is not replicated elsewhere.

“Invasive species are incredibly harmful to the ecosystem and to people, it hurts livelihoods, it hurts native species,” she says. “If it can be stopped before there’s a problem, then that is what you should do.”

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