Carnivorous snails
Most of the snailspecies are planteaters as a lot of gardeners can confirm,although a lot
of snails prefer soft,rotting plantmaterial.Occasionaly when they come upon a 
dead animal snails might nibble on it.Some snails and especially slugs who live 
most of the time in the ground eat worms.
There are a few snailspecies however who predate on other snails.One of the most 
well known is Euglandina Rosea(Ferussac,1821),the Rosy Wolfsnail.It is a native of
Florida,but has spread to other Southern States like Alabama,Georgia,Louisiana,
Texas and South-Carolina.

In 1955 they were introduced in Hawaii to control the Giant African landsnails that 
caused a lot of damage to agricultural crops.Although they ate some of the 
African landsnails other ,much smaller,snails became their prey too.
Some years later Euglandina rosea was also introduced in The Philippines,New Guinea 
and other islands in the region.
The Giant African landsnails were also becoming a problem in French Polynesia where 
they were being kept as a foodsource in the 1960’s and early 1970’s.
When farmers stopped the snails were released in the wild.With no natural enemies 
they reproduced rapidly and became a danger to crops.In 1977 Euglandina rosea 
was introduced to Moorea to cope with this problem.Even though they succeeded 
in reducing the African Landsnail population,other snailspecies such as the 
Partula snails were eaten too.The Partula snails were a much easier prey than the 
big African snails.
Scientists faced with the possible extinction of the Partula snails removed some of 
the population and started a breeding program in captivity.Now there are some 
Partula snailcolonies in a few Zoos.A 1987 expedition to Moorea failed to find a 
single living Partula snail.
More on Euglandina rosea here.

Another well known carnivorous snailspecies is Rumina decollata(Linnaeus,1758)and 
comes from the Mediterranean.This species has also been introduced to other areas like North-America,
were it lives in California to Florida and along the Atlantic coast north to Pennsylvania.
Even though they eat plants people say their preying on Brown Garden Snails(Helix aspersa)outweigh 
the possible damage.

More on Rumina decollata here.

A third carnivorous snailspecies living in North-America and Canada is Haplotrema concavum(Say,1821).
It is distributed from South-Canada to the Gulfstates and west to Nebraska and Oklahoma.It also 
lives in some counties in Florida.
Hubrecht(1985)says the snail feed more on shells than on living snails.
More on Haplotrema concavum here.