The northern Pacific island of Guam has become a nightmarish example of what can happen when a non-native species is introduced into the ecosystem — in this case, the brown tree snake.

In the 50 years since the semi-venomous snake arrived, probably on a cargo ship, it has killed off 10 bird species on the island and has nearly eliminated the remaining two.

The snakes are also affecting forest growth, which will lead to thinning and clumping of trees in the future, the Washington Post reported. This is due to the lack of birds, which eat the seeds of certain trees and then distribute them in their droppings. Trees that depend on the birds are becoming less numerous, losing out to others that are not so dependent.

The birds are also important for pollinating flowers and controlling some insects that feed on plants.

Before the brown tree snake arrived in Guam, 3,800 miles west of Hawaii, the island did not have predatory snakes. Thus, the birds were unafraid and unprepared.

The birds used to control the spider population, which has exploded in their absence.

Now Guam is one of the most snake-infested places on earth — with as many as 3,000 per square mile, some of them 10 feet long. The snakes are nocturnal and feed on rodents, lizards, bats and garbage. They can harm young children as well.

Haldre Rogers, a University of Washington doctoral student in biology who has studied the changes on Guam, recently told the Ecological Society of America: "Unfortunately, Guam is a laboratory of sorts for what happens when an invasive species brings major change. You can't really see it yet, but it appears that the indirect consequences for the forest can be as important as the direct consequences we saw on the bird population."

This is an extreme example of what invasive species can do.