Slugs and snails are soft bodied invertebrates found in great diversity. Although usually regarded unfavorably due to their damage to garden and productions crops, slugs and snails fulfill a wide variety of ecological roles. They aid in natural decomposition, seed germination and can be important food sources for animals and humans. Control of pest species involves numerous practices many of which are ineffective. Approximately 40,000 species of terrestrial slugs and snails are recognized.
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Slugs and snails are found in the taxonomic phylum mollusca, which means "soft." Mollusca is the largest group of animals second to the arthropods that contains the insects. Slugs and snails are also found in the taxonomic class Gastropoda, which is the second largest class of animals after the class Insecta. Gastropoda, which means stomach foot, comes from the way snails and slugs move on their ventral (stomach) side, which is called the foot.
Slugs and snails are most commonly known as garden pests, but most prefer undisturbed habitats and are rarely noticed by the casual observer. Examples of slug pests are the three-lined slug, leopard slug and reticulated slug. Common snail pests include the common brown snail, white garden snail, milk snail and vineyard snail. Most slugs and snails feed by scraping off pieces of food with several rows of microscopic teeth that can cause a lot of damage to plants.
The difference between a slug and snail is simply the lack of a shell on most slugs. Snails are identified based on shell characteristics, such as shape and color, as well as the external and internal anatomy of their soft body parts. Slugs are identified according to their soft body parts. Important external anatomical differences include size, color and mantle length. Internally anatomy is examined for differences in the genitalia. Many species are very similar, which can make identification difficult without molecular tools.
Numerous slug and snail control practices exist but few are effective. Practices include beer traps, eggs shells, diatomaceous earth, copper repellents, pesticides and removing potential habitat. All of these practices have been tested in scientific research. The only practices that have truly shown effectiveness are combinations of reducing habitat and using pesticides. Habitat reduction can include removing objects used for cover, controlling weeds, and reducing wet places by controlling irrigation. Mollusk pesticides (molluscicides) include formulations with metaldehyde, iron sulphate and methiocarb.
Slugs and snails can only partially control water movement into and out of their bodies. They produce slime (mucus) to reduce the rate of water loss and prefer to live in moist habitats. Snails use their shells for added protection against water loss. They also use mucus for locomotion by creating a thin layer to move over. Mucus is also used in defense and mate tracking as well as to find prey by carnivorous slugs and snails. Slugs and snails are hermaphroditic (having male and female reproductive organs) and display a wide variety of feeding behaviors.