Slugs and snails

| 7th March 2017
From front cover of 'Slugs and Snails by Robert Cameron, published by Harper Collins.
From front cover of 'Slugs and Snails by Robert Cameron, published by Harper Collins.
In this long-anticipated volume, Robert Cameron introduces us to the natural history of slugs and snails of the British Isles, writes Martin Spray, also venturing across the world to explore the wide range of structures and ways of life of slugs and snails, particularly their sometimes bizarre mating habits, which in turn help to illuminate the ways in which evolution has shaped the living world.
Dull? Snails? Think of what Cameron calls 'the baroque mating habits' of the common leopard slug Limax maximus, in which entwined pairs mate while suspended at the end of a long mucus rope - for hours on end.

New Naturalist volumes have always been notable. With 528 pages of small print, 190 figures, 51 tables, and 15 'boxed' texts, and at £35 (list price) for the paperback edition, number 133 is no exception.

I reckon its author is distinctly brave. This is one of the few volumes that does not present its readers with exemplars of charm and beauty.

Indeed, beyond the modestly pretty shells its subjects are not only the dull, miniscule obscurities that live somewhere in the soil, but also the shameful, miscreant, belly-crawling slime-devils - the slugs.

At least, that I think is roughly how these molluscs are imagined. Their reputation is terrible.

That is a mistake. Terrestrial molluscs include some very troublesome pests - most of them slugs. Yet the majority are innocent. They live lives that seldom cross ours, most are not very photogenic, many are difficult to identify, so we remain ignorant of and derogatory towards them.

That too is a mistake. The land-living molluscs are - bar insects, of course - about the largest group of land animals. Many have episodes in their lives that are fascinating. Many are amongst the unpraised and very largely unknown workers who ensure that nutrients are effectively recycled.

A world of slimy fascination

If you think them dull, think of what Cameron calls "the baroque mating habits" of the common leopard slug Limax maximus, in which entwined pairs mate while suspended at the end of a long mucus rope - for hours on end. Or contemplate the chains of mating pond snails Limnaea stagnalis one sometimes sees.

If you think of them as nothing but a disaster to human economy, think of the (very) common garden snail Cornu aspersum (better known as Helix), probably introduced to Britain by the Romans, as a food, and at least well into the last century known in the Bristol area as 'wall fish'.

Or if you think of them as dirty, disgusting propagators of Devil's slime, think of Martyn Robinson's experiments in 'Good house-keeping'. He used slugs to help keep his bathroom clean.

Not that these animals are uniformly innocents: a few species, most of them slugs, and most of them European, are notorious pests in field and garden, persecuting favourite flowers, mowing down seedlings, and eating potholes through potatoes.

In Britain, the relatively small Deroceras reticulatum, the grey field slug (still commonly known as Agriolimax), is the main - and almost ubiquitous - problem. It and several other European species have travelled with us around the world, and are now serious problems in many countries.

For instance, some slugs that frustrate British farmers and gardeners do the same in North America and the Antipodes - and it looks as though the 'control methods' available to us are not cost-effective.

The world's worst pest?

Even a very hands-on approach doesn't seem to work. I remember reading somewhere of the Leeds professor who each night for a year walked a particular route in his garden, gathering all the slugs he found. He destroyed 54,000 of them. He kept up the routine for another three or four years. In the last year, he destroyed 50,000 ... Replacements crawled up out of the soil.

Dull? Snails? Think of what Cameron calls 'the baroque mating habits' of the common leopard slug Limax maximus, in which entwined pairs mate while suspended at the end of a long mucus rope - for hours on end.

Yes: they are serious problems, but Cameron points out that none of them wins the World's Worst Pest prize. In fact, he stresses that "it is usually only a very small proportion of all primary production by plants that is consumed by slugs and snails." Although some are very much herbivores, and some are carnivorous, even cannibalistic, more are dependent on dead and dying plant material, or fungi.

Two other aspects bring problems - both at present relatively small, but potentially more serious. Like other animals, snails and slugs carry a diversity of other organisms, some of which cause disease or become parasites if transferred to humans. Fortunately, it is tropical and aquatic species that are most troublesome.

Unfortunately, our attempts at control of pest molluscs - real and imagined - bring yet more ways in which we release toxins into the environment, with consequences for wildlife and ourselves.

Horns do not a deveil make

Most of the book deals not with problems but with a predictable gamut of topics, such as anatomy, variation of morphology, habitats, contending with environmental factors, reproduction, history, dispersal, and colonisation.

A biologically interesting addition is the chapter 'Why be a slug?' - which less than a fifth of land molluscs are. One reason, a much reduced need for calcium, seems clear from the very large numbers of slugs compared with snails, on some highly acidic moors. Another likely reason is the ability to squeeze through the narrowest gaps - perhaps why Martyn Robinson found them in his bathroom in the first place.

The final chapter is 40 pages on "The uses of slugs and snails: practical, symbolic, poetic and recreational" - which I would say is in the New Naturalist tradition.

This is a bit of a ragbag chapter, but an intriguing one. Molluscs as food is picked up again here. The history of medical uses, especially the use of mucus to treat skin disorders, and their potential, are briefly sketched. Of other practical uses, I was intrigued to learn that leopard slugs were used by some troops in the First World War (from June 1918) to warn of gas attacks: they are more sensitive to the gas than are humans.

The chapter ends with a commentary on illustrations of paintings and manuscript drawings, and on poems and children's rhymes, that seems to beg the question I had when I began this review. What is our attitude to slugs and snails, and what do they represent for us?

They represent several contradictory things: slowness and sluggishness, certainly; and perseverance and reliability; and often cowardice. Because they emerge from their shells, snails came to symbolise the Christian Resurrection, and by extension, purity. And because they have 'horns', they stand for the Devil and for evil.

We clearly have an ambivalence towards these animals - at least in the European traditions, but with a tendency to think ill of them. I like the simpler emphasis of The Continuum encyclopedia of symbols (Udo Becker, 1992): "In numerous cultures the snail is a lunar symbol since it alternately shows and withdraws [...] itself. It is also a symbol of constant renewal." I would have enjoyed more on their uses, but that is not the purpose of the book.

I wish it was there for me in my student days ...

Cameron's style is a little dry, and often cautiously repetitive, I guess in order to build in more detail. I think he succeeds fairly well in making his admittedly somewhat offputting subject intriguing, substantial, and worth finding out more about.

New Naturalists are "a survey of British natural history", but Slugs & snails is almost as much an introduction to these animals worldwide. At times, it reads rather like a textbook, though an excess of jargon is avoided; much, however, is needed, not least to keep the word-count down. Fortunately there is a succinct glossary. I think the book will be of great use to students, at least those of zoology, ecology, and agriculture, if they want a textbook on terrestrial molluscs.

Robert Cameron writes with the care of an academic, but with the mission of a naturalist to sell his interest to others. In one way, however, he perhaps leaves by the wayside readers who have no basic knowledge of this group of animals.

Early in the book, he might, for example, have brought together a gallery of photos to illustrate the range and diversity of his subject, and to introduce their Latin names to us. as it is, they come at us out of the blue. Moreover, it feels as though half the names I became familiar with years ago have been changed, as we've learned more about these important but maligned creatures.

I agree with the publishers, that this is a long-anticipated volume. I wish something like it had been available when I was a student.



The book: Slugs and snails by Robert Cameron is published by William Collins in their 'New Naturalist' series.

Martin Spray is an editor and writer for Ecos - A review of conservation.

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