Fossil evidence dating back 550 million years identifies snail-like mollusks inhabiting the sea floor. Several million years later, snails adapted to land, breathing with lungs rather than gills. Snails now live in wide-ranging habitats from deserts to tropical climates, at sea level and in mountainous regions.
Related to other shell creatures such as clams and mussels, snails also claim squid and octopus as relatives. Slugs are snails without a protective shell. Land and sea snails rank second as the most plentiful species, following insects. Garden snails damage plants by chewing leaves, low-lying fruits such as berries and tomatoes and tree bark. Land snails encounter many predators, including rats, birds, frogs, beetles, ants and humans.