Snails ate my letter from Sir David Attenborough! Menace or a lesson in survival?

Snails ate my letter from Sir David Attenborough! The airmail envelope was sandwiched between glossy election pamphlets and moisture from a day of rain had added red ink stains to the manila paper. The exposed corners had been neatly chewed away. This was a serious case of the Aussie snail mail dilemma! ‘Have they no respect? I thought, cheerily’. Before I moved to Australia I never knew that snails could literally eat my post!

These snails were the common garden variety. They are the scourge of any gardener’s lettuce patch and introduced to Australia 120 years ago. You’d think such a small, slow-moving creature would be among the least successful animal on Earth but snails offer a masterclass in how to survive by not trying to change your world too fast. They are among the most ancient of our planet’s animals and we could learn from that.

Snail evolution

It’s thought that snails evolved about 350 million years ago about the same time as plants colonised the land. Their ancestors were already in the oceans. So, amphibious snails no doubt began grazing on fertile coastal algae, before ascending fully into the atmosphere. As regular readers of this blog know already, the evolution of land vegetation triggered a mass extinction event. Perhaps this could have been even more catastrophic if it wasn’t for the snails consuming much of the waste, laid down by plants in those early years.

Snails have been sliding across our planet’s surface for as long as any animal – even longer in the sea. The Golden-haired Snail, for instance, originates from a time before animals breathed oxygen.

These facts ought to be enough for snails to earn their reputation among the most noble of creatures. We owe part of our existence to the humble snail as much as any other animal.

Ultimate survivors

Let’s first dispense with a few myths about snails. They aren’t that prone to drying out. In actual fact, snail shells are impermeable, which provides them with a protective shield against the ravages of a sunlit world.

For instance, there are 2,500 known species in Australia alone. There are even snail diversity ‘hot-spots’ among the ancient rocky mountains and deserts of the Flinders Ranges. These same mountains harbour fossils of the oldest animals on Earth. If you’re familiar with the common garden snail you’ll know how they can secrete a hardened mucus to seal the shell entrance tight. Arid-zone snails in Australia survive decade-long droughts using this same technique.

The other myth about snails is that they don’t like salt. Of course, we all know, they originated from the sea. Among the greatest biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More of living animals in Australian salt lakes are snails like Coxiella. These can survive incredible salt concentrations and temperatures above fifty degrees. A bit of rain and they bounce back en masse. Beneath the black mud at the surface there are thick layers of shells and the animals wash up from time to time as ‘pink tides’.

When it comes to lifespan of a non-colonial animal, molluscs also hold the record for the animal kingdom. An Ocean Guahog (a type of clam) from Iceland reached an impressive 507 years old. Scientists aged it by counting annual growth bands on the shell’s hinge – which was then verified using carbon dating. The majority of gastropod snails, however, live only a few years. Though ‘Pet’ garden snails can live for 20 years.

Unfussy eaters

The eating habits of snails are diverse. The Otway Black Snail is a carnivore which hunts across the forest floor, searching out insects, slugs and worms, snaring them with long, sharp, backward-pointing teeth. It is a relict of a time before the mighty continents drifted apart 500 million years ago. A similar meat-eating species in New Zealand grows as long as a man’s hand!

The common garden snail is an omnivore and scavenger. This means it will eat anything including the rotting carcasses of dead animals. Its wide-ranging diet is a clues as to why we have the Aussie snail mail dilemma. If you add water to paper and glue, which can be made from corn, potato, tapioca, sago and wheat, you have made a delicious meal for a snail. It doesn’t even have to be that nutritious. In the wild, these animals can survive on very little, hibernating for several years at a time.

The king among snails is the giant African Land Snail which can grow over 20cm long. Most snails, like the common garden snail, feed on rotting vegetation. The African Land Snail eats plants and its introduction to parts of the US has made it a problem as they can infest native vegetation. It’s also said they have developed a taste for calcium-rich building materials including cement. Hundreds of articles online repeat the phrase they ‘can cause structural damage’. Though I cannot find any real evidence of this among the hyperbole.

Why do we have mail-eating snails?

Snails have proved for 350 million years that they are the ultimate survivors. If evolution has taught us anything, it is that slow and steady always wins the race. There is not much slower or steadier than a snail. So what of the Aussie snail mail dilemma?

There is an old Jimeoin joke that goes:

“When I checked the letterbox last night I found a snail eating my mail.
I said to it ‘you stupid snail, you’re supposed to eat lettuce, not letters'”

In our post-boxes we have provided one of the world’s most successful group of animals with the perfect micro-climate to survive. Then we’ve literally paid postal staff to deliver tasty food to them almost every day!

An infestation of snails in post boxes isn’t confined to Australia. Perhaps with climate change leading to a warmer, wetter world, this has become a more global phenomenon. Maybe snails will be among the likeliest to survive climate change and rebuild our world. I for one tip my hat to the snails and reckon we should be doing more to protect them.

The planetary scale of snail impact

I always like to finish up with an assessment of the impact animals have on ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More. It’s a bit difficult when we’re talking about an abundant small animal group. It’s harder to build numbers around that.

Suffice it to say, if you go outside now and lift almost any rock where there is an iota of moisture, you’ll probably find a snail. If you delivered post to that rock every day, that single snail would eat it. Now multiply that by the number of rocks on Earth – there’s your answer.

The Aussie snail mail dilemma really is a lesson survival. The impact of snails on our post might be inconvenient, but it is also a reminder, of how important they are to ecosystem processes.

The resilienceReferring to an ecosystem’s ability to maintain a steady stable-state. The need to build resilience is entirely anthropocentric and symptomatic of ecosystems that are damaged or declining, leading to loss of ecosystem services on which humans depend. More of snails to the most extreme conditions on Earth today is testament to their importance in our planet’s processes. Eating letters from Sir David Attenborough is behaviour at one end of a spectrum of activities they do. Snails are slowly maintaining and rebuilding our world through their extraordinary lives and diverse gastronomic tendencies.

Snails are pretty hardy, widespread and resilient. There isn’t much that we can do to stop the incessant march (or slide) of these animals across the planet. And we wouldn’t want to. We can’t survive without them.

The number of snails and other molluscs on Earth

According to some of the latest estimates, there may be over 340,000 species of mollusc (snails, slugs, squid, octopus etc). But there have only been about 85,000 molluscs described. According to Berkeley University, this is the breakdown of the number of known species of mollusc by group:

Molluscs account for about 0.2 gigatonnes of living carbon. For context, that’s about one fifth of the carbon contained inside all insect life, and about 3.3 x more than all humans put together.