Invasive frog species

Definition of invasive species from Wikipedia: Wikipedia definition

I found an article about invasive frog species in Florida  that they think floated in from Cuba thousands of years ago.  They are the greenhouse frog (Eleutherodactylus planirostris) and the Cuban treefrog (Osteopilus septentrionalis).

Scientists led by Blair Hedges at Pennsylvania State University analysed the frogs' DNA to identify the amphibians' closest native relatives, which would tease out clues about this unusual migration.
The greenhouse frog's ancestry was pinpointed to a small area of western Cuba, while the Cuban treefrog came from at least two sources in Cuba, of which the best bet is a remote peninsula in the western part of the island.
The team believe that the two species came to Florida thousands of years ago, quite possibly by climbing on board vegetation that then floated like a raft across the narrow strait.
Once established in the Keys, the frogs adapted over the years to the colder winters of Florida compared to their Cuban home, and this enabled them to spread northwards when transport and commerce links developed in the mid-20th century.

So The Scientists pretty much think that the frogs migrated to Florida on pieces of wood and other vegitation and when they got there they adapted to Florida's enviroment. Now they are invasive species.

"Both of them could have come across (to Florida) naturally, not by swimming, because these frogs would die pretty quickly in salt water, but by floating across on vegetation," Hedges said in a phone interview.

Many times species become invasive when they are transported to a place where their species have never been, and the other creatures there aren't used to it. They might steal homes, or food from other animals, or eat so much that other animals can't find any food.
Its a cool article: invasive floating frogs