Native to: Australia, Papua New Guinea, & Melanesia.

Introduced to: Guam, other Pacific Islands, Hawaiian Islands.

Mode of Transportation: The Brown Tree Snake was a stow-away on a military ship headed to Guam after World War II.

 
 

Before the Brown Tree Snake was introduced to Guam, there were no native snakes on the island. Since the island's animals hadn't evolved ways of defending themselves from snakes, they were easily snatched up and eaten by the invader.

The hungry reptile has killed most of Guam's lizard and bat populations, and has brought 10 of its 13 native bird species to extinction. The snake has also caused significant economic damage because it climbs electric lines and causes major black-outs.

  
   
  Since it's introduction, the island's Brown Tree Snake population has exploded. There are now roughly 13,000 snakes per square mile--the highest density of snakes in the world!