Leeches, beetles, caterpillars, flies, mites, shrews, mice, frogs, toads, snakes, other snails and a variety of various other birds, reptiles and amphibians are all natural predators to snails. Sometimes curious cats or dogs eat snails as well. Humans also consume a significant amount of snails as a delicacy.
Snails are a very common prey for many animals because they're extremely slow, making them an easy target. Because snails are small and easy to catch, it's common for larger predators, such as frogs, toads, snakes and birds, to eat many snails in one sitting. Snails are a popular target in shaded park areas where ducks and geese reside.
The snail's main defense mechanism is its shell. Although some animals are capable of breaking through the shell, the snail is often able to hide effectively from some predators in its shell. The snail's shell is also useful because it provides excellent camouflage in many areas.
Snails are a very important food source, and they help many species of animals to thrive. Although many are eaten, they mate several times a year and lay up to 100 eggs at a time, which keeps their populations strong in spite of their high mortality rate. Although humans consume millions of snails annually, most of those snails come from snail farms, so their numbers in the wild aren't affected.