Cost: The Brown Garden Snail reportedly costs California $7-10 million a year.

Major Concerns: Destruction of plant life, and disease spread.

It is not uncommon to plant a beautiful garden, only to find, a few days later, the flowers ruined by the handiwork of snails. They feast on everything from lilies to tomatoes, and are terribly annoying to both professional and amateur gardeners. Some snails are capable of disrupting the entire food chain. The New Zealand Mud Snail, for instance, was introduced in Australia, Europe, and North America. Without the necessary predators they bred quickly and eventually out performed other native species and insects for food. Once the insect population declined, the fish lost their food and begin dying off. This process eventually moved up the entire chain.

Other snails are capable of spreading diseases and parasites to humans. The most well known and dangerous of these is the parasite Schistosoma mansoni. Sometimes called the "blood fluke", it is passed to humans generally after swimming in snail-infested water and leads to Schistosomiasis. Over 200 million people are affected by the disease world-wide, which causes abdominal pain, diarrhea, fever, fatigue and possibly fatal diseases.