Are land snails declining and if so, why?



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    When many people think of snails they think of the aquatic, or water-dwelling, critters with shells. However, there are many species of mollusks that live on land. These are called terrestrial mollusks. Some have shells (commonly called snails) and others have no shell or just a small mantle (commonly called slugs). Land snails often live in moist areas, like rainforests and moist forests, but some species also reside in drier habitats.

    It has, in fact, been reported that land snails are declining around the world. However, in many cases it is not clear exactly why the snails are declining in population size. For one thing only a few people study snails. Overall, very little is known about the biology, natural history, and general daily and annual routines of most species. This makes it difficult for scientists to understand whether population sizes are cyclic, meaning they fluctuate from high numbers to low numbers naturally, or if something is really wrong. Furthermore, if a problem is discovered, so little is understood about the diet, reproductive methods, and daily routines of snails that researchers cannot raise them in captivity in hopes of increasing population sizes or saving a critically endangered species. Even if it is known that a population is in danger, scientists do not know how to save it!

    Once scientists determine that the snail population really is declining, it is equally difficult to understand why. Listed below are some examples of potential causes. However, it rarely is clear-cut. Sometimes more than one event is causing a decline and at times, one event can lead to or exaggerate another cause.

    Habitat destruction

    The human-caused destruction of habitat is negatively affecting species, snails and otherwise, around the world. Clear-cutting of forests, draining of wetlands, mining, construction, and many other human-induced activities drastically alter or completely change the habitat so that native species can no longer live in the changed conditions. Some organisms, like birds and many mammals, are mobile enough that they can move and find a new place to live. Snails, on the other hand, move slowly and have certain moisture requirements that do not make them as lucky.

    Introduced species

    Introduced species are those organisms that are brought to an area, either on purpose or accidentally, that, in some cases, take hold and begin to reproduce and call the new habitat home. Many times these species are invasive, meaning that they do well in the new area where their native predators are absent. They can complete with the native species, putting added pressure on the natives. Giant land snails have been introduced to some areas of the world and are having just this effect on the native populations. They are voracious feeders, wiping out food supplies and leaving the native species to die out. At times they will even feed on smaller species of snails!


    Many organisms are affected by disease as a natural part of their biology. This often weeds out weak individuals from the population. However, the presence of diseases has increased. This could be due to evolution of the disease, change in climate conditions making more favorable growing conditions for the disease, or the introduction of new disease along with the introduction of new species. At times diseases destroy populations quickly or at least weaken individuals so their predators can prey them upon more easily.


    Pollution is yet another factor negatively affecting many populations of animals, including terrestrial snails. Snails are sensitive animals that have certain temperature and humidity requirements. They need clean air and water within their ecosystem to remain in the best health. Pollution degrades waterways, results in smog, and coats plants with films of chemicals and debris. Environmental pollution, especially when coupled with another factor, such as habitat destruction, can be detrimental to snail populations.

    What can be done?

    It is important to expand our knowledge of terrestrial snails. This is accomplished through scientific research conducted by students, biologists, government agencies, and wildlife agencies. The more knowledge we can gain about the needs of the snails, the easier it will be to develop conservation and management plans to protect them. However, time and money are often limited, so research is neglected. We must make sure that science is well funded so we can help as many species as possible.

    Second, we must all strive to clean up our planet and save the natural areas. Recycle, pick up litter, do not pollute, purchase a hybrid car, and education your friends, family, children, and colleagues about the importance of protecting our planet. Every species and every organism is important in its ecosystem and we must stop species decline and habitat destruction.


    Land snails around the world are declining and we do not know exactly why! This is very scary because snails are important herbivores (plant-eaters) and prey for other organisms in the ecosystem. They have not been well studied and we do not know how to save them. Furthermore, snails are just one such example; there are many organisms in the same situation! Humans must make changes now to better our planet and further scientific research.

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