'**Achatina fulica**
is a very large snail found through out the world. It was imported as a food source, but soon became a pest. It lays between 150-1000 eggs (depending on age), just about every 3-4 weeks. They will eat just about any plant matter too.
They are illegal in the United States. If caught with them, you could be subject to a $5000 fine and up to 5 years in jail.
In the early 70's a young boy, from Hawaii, was visiting his grandmother in the Miami area of Florida, and brought a few with him (from Hawaii). She decided to let them go in her back yard and they soon became a major agricultural pest, destroying entire orange groves. It took the US millions of dollars and several years to eliminate the pest from the state. They were introduced to California around the same time, presumably on a shipment form a foriegn port. There too, they have been eliminated.
There are some pictures at this link that should really gross JenB out: http://www.geocities.com/Petsburgh/Zoo/9522/achatinaf.html