Study: Bullfrogs and snakes are invasive species that cost the world $16 billion.

feedhour feature image Guam is a small island in the Pacific. It is thought that as many as 2 million brown tree snakes live there now.

Scientists who looked at how much damage invasive pests do to economies worldwide found that two species cause more harm than any other.

Since 1986, the American bullfrog and the brown tree snake have caused $16.3bn (£13.4bn) worth of damage worldwide.

The pair is not only bad for the environment, but it has also destroyed farm crops and caused expensive power outages.

Researchers hope their findings will increase investment to help stop invasive species.

In a paper called “Scientific Reports,” the scientists said that the brown tree snake was responsible for the $10.3 billion in damage. This was partly because the snake spread uncontrollably across several Pacific islands.

The snake was accidentally brought to Guam by US marines a hundred years ago, and now there are so many of them that they trip over electrical wires and cause a lot of expensive damage.

One estimate says that as many as 20 brown tree snakes live in one acre of Guam’s jungle. This tiny island in the Pacific is home to more than two million brown tree snakes.

People think invasive species threaten island ecosystems because they make it more likely that native animals and plants will die out.

The American bullfrog has been known to eat almost anything, even other bullfrogs.

In Europe, the number of American bullfrogs has grown so fast that ambitious and expensive programmes are needed to control them.

Officials have had to put up expensive frog-proof fencing around known breeding sites to stop the spread of the amphibian, which can grow up to 30cm (12 inches) long and weigh up to 500g (17.6oz).

An older EU study cited by the authors found that it cost the German government €270,000 (£226,300) to fence off just five ponds to keep the amphibians from getting out.

People say that the frog will eat almost anything, even other bullfrogs.

Another species, the common coqui frog, was blamed for damaging the economy differently. Its loud mating song is thought to have caused property values to drop in areas where it has spread.

The people who wrote the study hope that the results will convince officials to spend more money in the future on pest control and other biosecurity measures.

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