While there are some terrestrial snails that are omnivorous and even carnivorous, most are herbivorous. Each species has a diet dependent on its size, age, habitat and individual nutritional requirements. They all must feed on foods that include significant amounts of calcium in order to keep their shell hard.
Those species that are herbivorous consume a variety of plants, including the leaves, stems, bark and fruits, as well as fungi and occasionally algae. They do so in an unusual way. Snails have an organ in their mouth with rows of tiny teeth, called a radula. When the food reaches this structure that looks like a sack, the teeth do not cut or grind it like human teeth would. Instead of being chewed, the radula scrapes the food and breaks it down before it passes through the esophagus to continue the digestion process.
The tiny teeth on the radula suffer much wear and tear as time passes. Therefore, they are continually replaced by others. Not all species have the same number of teeth. Some have rows with just a few teeth, while others have hundreds.
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Ground beetles (family Carabidae) are fast moving beetles, many of which are predators with specialized diets. One ground beetle (Cychrus caraboides) eats only snails (its head and thorax are very slender, allowing access to the inside of a snail’s shell). Another, Harpalus rufipes, limits its diet to strawberry seeds. Loricera pilicornis uses bristles on its antennae to trap springtails and mites.
The Bronze Carabid, Carabus nemoralis, (pictured) uses its large curved mandibles to crush and slice through prey – it will eat or try to eat just about any invertebrate, but specializes in capturing and eating slugs. Its hardened forewings, or elytra, have a coppery sheen to them, and parts of its thorax and the edges of its elytra are iridescent purple. This nocturnal, introduced, flightless, one-inch-long beetle resides throughout the Northeast and is already actively pursuing slugs.
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Most terrestrial snails are herbivorous, feeding on a wide range of vegetation. The snail’s mouth is on the bottom of its head near the shorter pair of tentacles. Snails (and all molluscs) consume their food not with mouthparts, like insects, or teeth, like mammals, but with a rasping tongue or radula. Snails don’t bite their food, but rather, rasp or scrape it. The radula is covered with rows of tiny “toothlets” which rasp particles away from vegetation and move them back towards the snail’s gullet. Different species of snails have differently-shaped toothlets. The radula is used by the snail not only to process food, but to clean bits of dried mucus from its shell. Supposedly if you listen hard, you can actually hear a rasping sound when the latter is occurring. (If you look hard, you can just barely see the orange radula of the land snail in the photograph.)
Snails and slugs are grouped together as gastropods – a class of Mollusks that includes land, freshwater and sea snails and slugs. The term “snail” is used for species with an external shell large enough for the soft parts to withdraw completely into it. Those gastropods without a shell, and those with only a very reduced or internal shell, are usually known as “slugs.” We refer to many marine gastropods as seashells, including whelks, conchs, cowries, olives, cone shells, figs and tulips. While many gastropods are herbivorous grazers, several groups are carnivores, capable of drilling through the skeleton of their prey.