It isn't every Thursday morning that one makes a paradigm-destroying observation while rushing, umbrella-in-hand, to one's car. But that is exactly what happened to me last Thursday. It was pouring with rain, I was running six minutes late for work, I was wet and cross about it, when suddenly, there it was, as bold as brass and as bright wet as day, in front of my very eyes: a common (but, until that point, not at all garden) snail, Helix aspersa, sliming its way across my driveway.
You have no idea how ridiculously happy this made me feel. It is six years this month since I moved to my home in the Yorkshire Pennines, and, in all that time (with one very minor exception), I have seen (if you'll forgive the inappropriate cliché) neither hide nor hair of a snail. And, believe me, I've looked.
I first wrote about the lack of snails in my garden in 2002, in an essay entitled …So Let's All Be Scientists! It was my contribution to Darwin Day Collection One: The Single Best Idea Ever [ISBN: 0972384405, Amazon.com], a collection of articles, reviews and cartoons in celebration of Darwin and science. In the essay, I suggested a number of hypotheses—some of them more serious than others—why there were no snails in my garden.
Until 06:16 last Thursday, the acidic soil hypothesis (i.e. the acidity of the soil preventing snails from forming shells) was my favourite explanation for the dearth of snails, but that has had to go by the wayside. I am now beginning to favour the out-competed-by-slugs hypothesis. For the first four years that I lived in this house, the garden was literally plagued by slugs: thousands and thousands of slugs. But, for the last two years, the number of slugs has dropped considerably. I'm not sure why this should be—a combination of an unusually dry summer last year, and more dilligent weeding by yours truly is my best guess—but maybe the marked drop in slugs has let the snails get a (literally) single foot in the door. A Darwinian mollusc war in my own garden: who'd have thought it?
I will continue to monitor the situation with renewed interest.