Snails

by Dennis McNair, PhD

Snails, like slugs (which are just snails without shells), are gastropod mollusks. That means they're biologically classified as being in the Phylum Mollusca (along with squids, oysters, etc.) and Class Gastropoda (“gastro-“ stomach, “pod” foot). Snails and slugs are the most numerous, in both numbers of individuals and numbers of species recognized, of this large phylum of invertebrate animals. 

Many gastropod species are considered to be harmful because they feed on tissues of domestic (and other) plants by rasping away at their tissues with their file-like tongue, or radula. They glide along by using oar-like cilia on their undersides that propel them over a layer of mucus that they lay down themselves. Their bodies generally are covered with a mucous coat, especially on the parts they use for locomotion, so they appear to be quite slimy and exist, largely, in moist environments or in fresh or salt water.

Around the world, a few species are considered edible, and in European cuisines, escargot (snails cooked in a garlicky sauce) is considered a delicacy. Consumption of other gastropods, such as marine conchs, is common, and several bivalve mollusks, such as clams, oysters, mussels, and scallops, are economically and gastronomically important seafoods, as are some cephalopods (squid and octopuses).

Unfortunately, for the control of mollusk garden and crop pests, such as slugs and land snails, many molluscicides employed in the past have been demonstrated to also be toxic to humans and our pets. Recent control methods avoid such clearly harmful effects. In small gardens, a dish of stale beer (or sugar-water with a little yeast sprinkled in it) seems to lure snails and slugs, and the animals drown in the attracting liquid.  Some of the often-used commercial molluscicides have little long-term efficacy or have been assessed against only a few species of pests, so we are unsure what their effects might be on other animals, especially over prolonged periods of use. Hand picking and removal is repugnant to many and can be time consuming in large gardens. Snails are also intermediate hosts for several organisms that cause human and domestic animal diseases or fatality (e.g., schistosomiasis, liver and lung flukes), and cost/benefit analyses skew values in such situations.  Fortunately, snail garden pests don’t fall in these categories, so prudent use of remedies such as stale beer can rid us of these pests safely.

In 2016, author Elizabeth Bailey wrote a lovely book, The Sound of a Wild Snail Eating, based on her observations of a snail at her bedside during a prolonged illness that kept her bedridden. As with so many ruminations on natural phenomena, Bailey found her experience to be deeply relaxing, and she credits the snail with allowing her health to be restored. Psychologist Dacher Keltner, a recent speaker at Chautauqua on the subject of Awe and Wonder, would, no doubt, agree with her.  (On the other hand, I once met a malacologist – a scientist studying mollusks – who was trying to raise funds to protect several endangered species of Banana Slugs endemic to the San Juan Islands in the Pacific Northwest. He was having extremely limited success!)

Snails’ legendary slowness and resolute pursuit of objectives probably account for their evolutionary success, as demonstrated by their persistence (over 65 million years) and diversification (80% of the species in the large Phylum Mollusca, estimated to constitute from 40-100,000 species, most of which have never been scientifically described).  For all these reasons and more, snails undoubtedly deserve our observation and admiration instead of our disdain based upon their sliminess and the damage they occasionally do to our gardens.