Molluscs are a category of invertebrates (organisms with no backbone) that possess a soft body as well as a shell. The shell may be either internal or external. Molluscs come in various shapes and sizes and are capable of living anywhere. Only snails and slugs, however, live on land. Land slugs may have an internal shell or no shell at all, therefore they are susceptible to drought and predators, and thus most species in the Mediterranean are cave dwellers or nocturnal to avoid the heat of the day, and unpalatable or poisonous to avoid being eaten. Land slugs are generally found near decaying plant matter or in the soil where it is most moist. Land snails afford to be more versatile regarding where they can live due to their prominent shell. Land snails, like slugs, need moist environments to be active, and tend to be more edible to non-arthropod predators, but they can survive drought in aestivation mode due to their shells, even in exposed areas like dry tall twigs where slugs do not dare to venture. Snails and slugs are collectively known as gastropods. These slow-moving molluscs, snails being the faster of the two, are all hermaphrodite, meaning that each one is both male and female. Therefore, when gastropods copulate, both individuals get pregnant and lay eggs.
Being slow organisms may not make them very dispersive, but their reproductive biology ensures that some species will remain plenty in number, and this is why some have become agricultural and horticultural pests. Locally there roughly 60 species of terrestrial gastropods, most are rare and very small, localised in natural habitats, seldom seen, some are frequent, some are endemic. Only the very few common ones often do damage to crops, or are seen as unwanted guests in households. The largest and most common of the snails is the Edible Snail, Għakrux Raġel (Helix aspersa), which is the also collected in large numbers as a food delicacy. Other smaller but common species are the Red-banded Snail, Għakrux Mara (Eobiana vermiculata), the Goat Snail, Mogħża (Helix apertus) and the endemic Maltese Marmorana, Bebbuxu tal-Bejt (Marmorana melitensis). These species are all herbivorous and detrivorous, therefore all might resort to eating leafy material in gardens, but the most voracious remains the Edible Snail. A very small common snail which is found under pots in gardens or in crevices is the Clivenden Snail (Papillifera bidens). Other gastropods that like being in gardens and under pots are two common slugs: the Common Slug, Bugħarwien tal-Bjar (Limacus flavus), and the Black Wedged Slug, Bugħarwien Iswed (Milax nigricans). A species which manages to control the common snails, besides man, happens to be a gastropod itself, the Decollated Snail, Trajbu (Rumina decollata). The best mammalian predator for snails is the Vagrant Hedgehog, Qanfud, (Erinaceus algirus).