The Snail - Pest, Pet or Treat? Some Interesting Facts
Sunday 31 July 2016
Snails that live on land have been around for quite a while, around six hundred million years which puts our species a little to shame. Although there are many more species of snails that live in water, it is the land snail that most people know well. Many shudder at the thought of the sliminess of the creature, others have nightmares about them. However, there are many aspects of snail life that will surprise. Seen up close, too, the shells of these gastropods are often things of exquisite beauty.
The largest land snail is the Giant African (Achatina sp), which can measure up to thirty centimeters in length. It can also be eaten and is a fantastic source of protein - as you might expect from something so large. A native of East Africa, many people now keep these as pets, although it is illegal in the United States. When bred in captivity they are easy to keep and free from parasites and disease so are quite harmless. You may not like the idea of one crawling over your foot, however. Where sold as delicacies, they are often cooked, sliced and even canned.
Most snails have one large foot and this is what a lot of people dislike as it needs to be moist to move. This means that the snail lubricates its foot with mucus and leaves a trail behind it. The mechanics of the foot, however, are a triumph of evolution. The muscles contract in wave after wave which moves centrally down the foot, enabling it to move.
Take a snail and stick it on some glass to see this movement in action – it is almost hypnotic. The mucus makes sure that there is little or no friction to hinder the snail but it also makes it very difficult for the snail to be injured. In this way it is quite possible for a snail to move comfortably over a razor blade – but perhaps best not to try this at home.
In fact, it is probably best not to touch snails at all, if you can help yourself. It stresses them out. When you pick a snail up it often produces bubbles or foam which is a form of defense. It could also be that they have detected a substance on your hands - soap for example - that they don't much like.
Snails are good mathematicians even though they may not appreciate it themselves. As they grow, so do their shells which are made from calcium carbonate. The formation of the shell is what as known as a logarithmic spiral. This is where the distance between its spirals increases progressively. Although the snails do it approximately, logarithmic spirals can be represented by complex mathematical formulae. Basically, the size of the spiral gets bigger and bigger but its shape remains the same.
So what stops a snail from growing to gigantic proportions? Apart from the necessities of its environment, when a snail species reaches its full size then a thick lip grows at the place where the shell opens. This means that it is time to find a friend and reproduce. So, on small immature snails you will not see a lip – you can tell if they are babies whatever the species.
Another thing about snails that a lot of people find frankly unappetizing is their tentacles. Even the word can send a shiver down many a spine as they imagine being wrapped up by these appendages and devoured as lunch a short time later. Hyperbole aside, most snails living on the land have two sets of tentacles. The upper pair are their eye stalks – or if you want the scientific name, they are ommatophores. They are usually about three quarters the width of the eyes which is why you get the bulge at the top. The lower pair is used to smell out their food. Snails can sense vibrations with these tentacles, which can retract when the snail perceives danger, even though snails cannot hear.
Most terrestrial snails are herbivorous which means that they eat plant matter, so the fear that the snail may start eating you if placed on your hand (or elsewhere) is wholly unfounded. One or two land snails are carnivorous, but they will still not attempt to eat a live human. In fact, although land snails live virtually everywhere – from high up in mountains to the heat of the dessert - the species that we see around us are found close to our homes. You could almost say that they like the company of humans, but most scientists would refer to them as anthropophilic.
Have you ever heard a snail eat? It's possible. The snail attacks it food using the radula, which is made of tiny hooks. In this way it doesn’t really bite in to food, but rather scrapes at it. The bits that it tears away are then sent straight to the digestive area (known as the tract). So, next time you find yourself next to a large land snail (in a very quiet area) see if you can hear it scraping away at its food. It won’t mind – its brain is so simple (even though it is divided in to four separate areas) that it will not sense you as a threat. Snails can learn by association though. Think of Pavlov and his dogs, dumb it down a lot and you are in the right ball park.
Sometimes, though, it really is simply dog eat dog.
Man species of snails will sit out the winter in hibernation. They will also, during long hot summers, occasionally estivate. Estivation is not something of which many people are aware – but it becomes self-explanatory when given its common name – ‘summer sleep’. A snail will go in to a summer sleep to avoid the high temperatures and to risk becoming too dry (dessication). For many snails, estivation will save their lives as to keep their shells in tip top condition they need a lot of calcium and in dry times this can be harder to come by. The snail will seal itself in by drying out a layer of mucus over the entrance to its shell. This is called an epiphragm and many people, when they see a snail like this, believe it to be dead. No – it is only estivating.
All terrestrial snails are hermaphrodites. This means that they have the organs to reproduce which are normally associated with both the male and female: it does not mean that they can mate with themselves. When you see a pair of snail mating, that they are inseminating each other. In other words, snail A will fertilize the eggs of snail B and vice versa. They will then lay anything up to a hundred eggs each.
Snails do not lay their eggs on plants like other species such as butterflies. They lay their eggs in loose topsoil. This is one of the reasons they like living close to us – our farming and general plant-growing means that the soil is often turned and so is nice and loose for the eggs to be laid – way down – up to ten centimeters below the surface.
These eggs will hatch in around three weeks. Many land snails are fecund in the extreme – they will mate and lay eggs around once a month. No wonder gardeners and farmers don’t like them much as that means, collectively, they can scrape their way through an enormous amount t of food.
When the baby snails emerge they will eat the remains of their eggs as it is a great source of calcium and they need this for their shells to grow. For a few weeks they will look transparent to the human eye, but then their shells will turn to the usual color. It has been recorded that herbivorous snails will eat any unhatched eggs that are around which is a form of cannibalism. When the shell turns color they effectively look like tiny versions of the adults (even though sometimes the body looks too long to go in to the shell). It will be at least a year before they are ready to breed themselves.
Snails are eaten in many European countries – the most familiar being the French escargot where they are served in garlic and parsley sauce. To get the snail ready for the pan they must go through, first of all, a nil by mouth system where they are only given water for a few days. After that they are fed on only flour or water for a week. This is to clean out the snail, effectively, because otherwise they would be cooked with all their waste product still inside and so would not taste particularly good.
Other snail eating cultures include Greece, Cyprus, Spain and Italy although lesser known traditions do exist in northern European countries such as Germany and the United Kingdom. They must be cooked properly as if not they can cause a form of meningitis. So if your instinct is to avoid having them for lunch, perhaps you're right.
We couldn't leave with snails on a plate. So here's a picture of a woodlouse on a snail on a snail. Just because.
First Image Credit
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