Results
We used garden snails of the same species. (Helix aspersa) and roughly the same size and age. We were able to do this because we breed snails here at Gribblybugs.
We found that most of the barriers were ineffective and the control snails actually seemed to be attracted to the coffee grounds. The petroleum jelly was crossed in a matter of seconds by all of the snails we tried and the ground coffee barrier was consistently breached in less than a minute. One of the snails was reluctant to cross the egg shells completely, although it did stop to eat some of the shell.
Another snail seemed to crawl onto the shell and eat before for about 40 seconds before breaching the barrier completely. The kitchen foil was breached in under a minute, although there was some initial reluctance to pass onto it. The sand was also ineffective as a barrier, taking less than a minute to breach. The Ground ginger was not completely breached in the 3 minutes, although the snails did test it and move onto it, they also reared up and retreated back into the centre of the circle. The snails with ginger on their bodies were washed immediately after the experiment. The ground garlic was the only completely effective barrier. The snails seemed repulsed by the smell. They would not touch the garlic and continually retreated back into their shells or made circling motions within the centre of the circle. One of the snails made foam (a defensive reaction to certain chemicals).
This snail was washed after the experiment in clean running water, as a precaution, but demonstrated no ill effects afterwards and whizzed about the control area and even went over to and breached the ground coffee barrier from the outside in.
Our conclusion is that the only effective natural barrier, of those tested, was ground garlic. The experiment could be improved by using tighter controls and removing other variables such as strong smells nearby or inconsistent lighting. It could be tried with different species of snails.
