My fascination with snails began when I was four years old. Even at that young age, I was fascinated by their clever means of locomotion, sliding along on their own river of slime; by their eyes, which disappeared down into the hollow tube of their tentacles when I touched them. Their shells, particularly, caught my imagination. What fun it would be to have my own little house that I could disappear into when my parents called me to go indoors at bed-time!
For many years afterwards snails were out of sight and out of mind, and remained so until, in 1994, I finally settled in my present house in Devon. For the first time I had my own garden and was growing my own food! It was then that these cute little creatures, with their clever design and attractive shells, suddenly revealed their true colours. I rapidly learnt that gardens and snails do not mix. They had voracious appetites for my favourite flowers – lupins and delphiniums – and for my precious vegetable seedlings. They loved the Devon soil: a rich, heavy clay which was wonderful for brassicas but also for slugs and snails. The previous owners had landscaped the garden using large amounts of stonework – perfect hiding places for Molluscs. The plentiful rainfall kept them active and their energy level was terrifying – far surpassing my own. I just couldn’t keep up with them: I was soon exhausted by my futile efforts to protect my plants (figure 1).
figure 1: The author in the rain collecting snails in her garden.
Every spring, I planted out the seedlings that I had lovingly nurtured in my green-house; and every spring, within two days, they would be shredded to bits by snails and slugs. I had expected slugs to behave in this reprehensible manner, but somehow imagined that snails were more considerate. I felt quite betrayed by my childhood pets.
From then on, I changed from peaceful snail fancier to snail- murderer. I went through many stages of shameful snail- bashing. First stop were the blue metaldehyde pellets, but I hated removing the slimy green corpses from the soil. I began to worry what the pellets were doing to the wildlife in my garden: to birds and worms, and just as importantly, to the organisms that kept the soil healthy.
Very soon, I turned to organic gardening: this seemed a sensible compromise. I was still killing snails, but in a more sustainable way: beer traps would at least provide a happy death. By such double-think, I salved my guilty conscience. Yet my snails refused to die, merely gulping the beer as an aperitif before their main meal: my lettuces. Nor could I bear to crush them by stamping on them, as my tutor on an organic gardening course advised. I decided that all this killing was wrong, so I spent a fortune on barriers such as grit, gravel, egg shells, copper tape, drain-pipe moats, and Vaseline to smear on the pots. The list was endless, but my patience and time and finances were not. Moreover, the main problem was that none of these seemed to work. The snails were too devious, happily whizzing up my flower pots over the slippery Vaseline surface as if I had provided them with some extreme sport.
There had to be another way that would suit my snails, my garden and me, enabling us all to live peacefully together. By this time, I knew that the garden snail, Cornu aspersum was the main culprit. I began to collect them all up and take them away to a piece of nearby wasteland, about quarter of a mile away. This I did on a more or less regular basis for two or three hours a week. Over the years I had heard amazing anecdotes of snails returning from distances of up to three miles. Now I wanted to find out for myself if these stories were true.
I started to mark them with red nail varnish, putting a small blob on each shell, before releasing them on the waste ground. I never saw them again. This was good news for my vegetables, but by now I was curious: I wanted to know whether their disappearance from my garden was due their having to ‘home’ over such a long distance, or whether they had been eaten by predators. I decided that I needed to tackle this problem more scientifically. I would remove the snails to a much nearer patch of waste ground, just beyond the end of the cul-de-sac where I lived. This would give them a sporting chance of returning home. By this time, the spirit of scientific discovery had far superseded my concern for my blitzed lettuces. Bizarrely, I was almost hoping they would return!
I persevered with my very unscientific experiments, working by increments of a few metres to a final release point of up to 30 m away. But my options were limited: short of chucking them over the neighbouring fences, there were not many nearby places to dump them. Moreover, at this stage in my scientific career I was totally ignorant about the importance of controlling for different variables such as terrain, and weather conditions.
My career as amateur scientific sleuth would have come to nothing, had it not been for an incredible stroke of luck. I was a keen listener of the BBC Radio 4 programme, Material World (MW). One day, in December 2009, I heard on the programme that the MW team were running an event called So You Want To Be A Scientist (SYWTBAS), designed to expose amateurs to the wonderful world of scientific research. I entered with my idea: to find the homing distance of the common garden snail, C. aspersum. To my delight, the judges liked my idea. I was selected as one of four finalists.
The producer, Michelle Martin, warned me that the competition would involve ‘a lot of hard work.’ Little did I suspect how much. By the end of the summer my brain was totally stretched and wrung out. The main challenge for me was trying to mould my scatty, unscientific thought processes into some semblance of linear, logical order.
Fortunately, help and support were on hand in the form of Dave Hodgson, the mentor assigned to me by the Material World team. Dave is a terrestrial ecologist and statistician, lecturing and researching at the University of Exeter’s Cornwall campus: the Centre for Ecology and Conservation. One fine day in early May 2010, Dave and Michelle came down to Devon to check out my snails, my garden, and me. We discussed how we would proceed with the experiments.
At this stage, my total ignorance of the scientific method was revealed: I did not even know what a data-set was. However, what I had realised by this time was that before measuring homing distance, it was first necessary to prove that snails did in fact have a homing instinct. To do this, we had to establish a ‘home’ for the snails: i.e. a small area about 1 metre square in which to place plants attractive to snails: a large basket of Surfinia and a pot of Hosta. Once the snails had populated their new home, I collected a sample of snails from elsewhere in the garden, preferably from the opposite direction to the home base.
figure 2: Getting ready for the 4th instinct experiment in neighbour Sue's garden.
Then, in the middle of a large tin tray, chosen for its smooth surface (figure 2), I marked a large circle with all the compass directions (N, NE, etc.). Now the fun began. I hunted for the little pioneers which would make Mollusc history. The home snails were either hiding in the petunias or hostas, or in their ‘shelter’ about a metre away – in this instance, a clump of day lilies. The ‘away’ snails were collected from 8 m away – a patch of Phygelius, another shrub with tall leaves. The tray was placed exactly between the two collection points; each sample was marked with two different colours of nail polish (figures 3 & 4), and then set down in the centre of the tray and released.
figure 3: Marking snails for my 5th instinct experiment.
figure 4: C. aspersum exploring kitchen roll before the 5th instinct experiment.
This was the hardest part, because I also had to track their initial direction of travel to see if there was a correlation between this and where they ended up. The snails were moving so fast that I could hardly keep up with them: as soon as I marked their exit point with a cross on the periphery of the circle, another couple of snails had hot-footed it to the other side. They all scarpered across the smooth surface like bats out of hell. To complicate matters further, they piggy-backed – presumably to save mucus – and thus a pagoda of two or three snails would leave the circle at the same time. (Scientifically, how was I to record this, I wondered?) Then, annoyingly, three or four would remain curled up in the centre, refusing to move; I had to hang about for hours to make sure they didn’t scarper the minute I went inside to make myself a cup of tea.
However, the results were worth the hassle. From my first instinct experiment, 8/14 snails, originally collected in the ‘home’ patch, returned ‘home’. None of the ‘away’ snails set up camp in the home patch. In the ‘away’ location, 9/26 snails were recovered, plus 1 from the home base. Many snails were found to have returned to their original bases, and there was an almost complete absence of ‘cross-over’ between the two locations.
In my second instinct experiment, 8/10 ‘home’ snails were recovered, all from their home base; and 7/ 8 snails were recovered from ‘elsewhere’, but only one of these was found in the home patch.
At this point in the experimental process, I was dragged screaming and kicking into the scary world of statistics. I had to get my head round the p-value (probability value), derived from Fisher’s Exact Test. P-value is based on a null hypothesis: that is, that snails do not home: i.e. that they are no more likely to travel home than to move away. The alternative hypothesis postulates that snails tend to move towards home. As Dave explained: ‘The probability of getting a result so biased in favour of the homing instinct hypothesis, if the null hypothesis is true, is only 2 in 1,000, or 0.2%; so we can be confident in rejecting the null hypothesis.’
It was necessary to do three further instinct experiments to ensure that these were not just weird snails. The findings from two of these experiments showed strong evidence in support of homing, but none of the three produced such startling results as the first two. This was due mainly to a heat-wave in mid-summer: snails disappeared into cracks and crevices to aestivate. Even so, I was learning a lot about variables such as weather, barriers, time of day, and how they affected our experiments.
The research was now opened up to the public, who were encouraged by the MW programme to take part in a national on-line experiment called The Great Snail Swap. Neighbours were invited to find snails from a location in their own gardens, and then, with each sample marked in a different colour, to swap them over – and then release them in the opposite location. There was an on-line questionnaire to record when the first snail returned to its original base, and drop-down options to record the different variables, for example, weather on the day of collection, and barriers (such as wall, fence, or building).
Once more, the results from this questionnaire were weighted in favour of the homing theory, with returns of up to 30 m reported. But it was very disappointing that in spite of repeated reminders on the Material World programme during the summer, few listeners bothered to take part. Maybe British reserve triumphed over scientific curiosity, and neighbours just didn’t fancy getting too chummy.
One experiment which proved to be a resounding success took place at my local school, St. John’s. I had spoken to the staff, in particular to Rachel Azzopardi, the Year 4 teacher, and asked if St. John’s could be the pilot in a series of school experiments that could be ‘rolled out’ nationally. Rachel was very enthusiastic and prepared an excellent lesson plan, explaining the scientific method, as well as all the interconnected disciplines of science which would be involved: maths, compass directions, ecology, maps, and snail anatomy and behaviour. One sweltering day in mid-June – the hottest day so far – 30 children, aged between 8 and 9, assembled in a quiet, separate area of the school playground. Here, a number of compass circles had been marked on the tarmac, which sizzled with the heat. The pupils had already collected a sample of aspersas from their gardens, and marked them with a wondrous array of different designs and markings, one for each child. They were divided into small groups, each with a scribe to take notes. With mounting excitement, the snails were released in the centre of their circles. First, the children watched ‘their’ snails to see in which direction they were heading and to see if it correlated with their homes. The next half-hour was organised chaos. Children ran around with watering cans to cool the tarmac and the snails, which struck off in different directions (figure 6). Some, their owners affirmed, were heading straight home. A few, unfortunately, got splatted in the excitement (the snails, not the children). The findings from this experiment were interesting. At least three of the snails made it home, according to the testimony of the more reliable members of the class. One almost called in at the local Spar shop, another tried to cross Totnes Bridge. As one member of the class lived 12 miles away in Torquay, it was no surprise that this child’s snails found the journey too much of a challenge.
figure 6: St.Johns - the snails decide on direction a.
As a scientific experiment, the results might be inconclusive – but as an educational experiment it was superb. It was a joy to watch the class. Every child was fully engaged, active, and concentrating well, besides learning much more fascinating science than is usually possible to pack into an afternoon’s teaching. It was the perfect example of the ‘outdoor classroom’ in operation.
The summer ended with the SYWTBAS competition final, in September at Aston University. I was indeed fortunate to win, as the other three finalists all had interesting projects and gave excellent presentations. I certainly could not have succeeded without the help of Dave, Michelle, and the Material World team, who were always on hand with reassurance and support.
The results of our research have been very satisfactory. We have found strong evidence in support of homing instinct, and homing distance up to 30 m. On a practical level, this suggests that gardeners could take their snails away to a distance of approximately 100 m – just to be on the safe side! We also learnt that snails are faithful to their feeding and resting sites, but many disappear, and others replace them. Future experiments could explore population size and abundance.
More research on homing needs to be done. This is currently happening under Dave’s direction at the Centre for Ecology and Conservation in Cornwall, where experiments are taking place using an increased testing distance. Also at the centre, there has been a very interesting development from the instinct experiments that took place on this site in July, 2010. Six months later, new returning snails were found back at their original locations, suggesting a very long journey home – and reminding us once again that all experiments must happen at a snail’s pace, and that patience is a virtue.
The implications of our research go well beyond the establishment of a homing distance for C. aspersum. Our findings open up much wider ecological issues. It gives us gardeners choices as to how we deal with unwelcome garden ‘pests.’ We can choose to be kinder to the wildlife in our garden, including the micro-organisms in the soil, by choosing alternative methods of snail disposal. Best of all, we can feel happier in ourselves in that we are helping to maintain the tiny eco-system that is our garden. The next step in my own scientific journey is to disseminate my findings to a wider audience: hence, this article in my new favourite magazine. In collaboration with Dave, I also hope to publish our findings in a scientific journal. I have discovered that the scientific process has no ending: my simple question about homing instinct in snails has opened up new questions, new opportunities and new discoveries. Aren’t snails amazing!
figure 7: BBC News – Dave Hodgson, Cameraman Martin, and Pallab Ghosh filming in Ruth’s back garden.