How I learned to value slugs and snails

Researches and Discoveries in the Garden

Slugs and snails must be among the most visible, and certainly the most infuriating of pests for the organic gardener. The demoralisation of seeing the telltale slimy trail, and the remains of a lettuce or runner bean crop, is a common experience. I love the idea of growing my own food, but until two years ago it never exactly came to reality. And the reason for the failure was largely because of the slimy little blighters. I gave up even trying with supposedly simple crops like spinach or lettuce. I unwillingly shared my potato crop with the garden molluscs. My tomatoes and runner beans had major fortifications around them (moats, stilts, copper tripwires, sawn-off plastic bottles and bits of plastic drainpipe as collars around the plants) until they were robust enough to survive unassisted. It was a continual battle. I squashed the tiny slugs or snails I found around the plants I wanted to keep, and threw the larger ones in the compost bin, on the basis that they might usefully chomp something there.

However, I had a nagging suspicion that the remedies I was using were dealing with symptoms and not causes. What is it that prompts slugs and snails to do so much damage? Last year I inadvertently stumbled on a possible explanation.

For reasons unconnected with molluscs, I started using copper garden tools in the garden in spring 2001. By August I noticed that the potato crop on a small raised bed was doing well, and put it down to the quality of the manure and the fact that I had earthed them up with grass clippings. There were so many potatoes that they were pushing through the surface, so I started picking them off, trying to avoid disturbing the roots. Then, ever optimistic, I sowed some lettuce seeds in the greenhouse. A week later they had started to sprout, and late one night I did a prowl with the torch. I found two large slugs in the area, picked them up and deposited them in the compost bin. Ten days later the lettuces were still there, such a surprising event that I didn’t know what to make of it. In the absence of any other course of action, I promptly forgot about it. At the end of August I harvested my potatoes, and by this point I realised that something decidedly strange was going on. Even having had several meals from the potatoes I had already picked, there were still 36 pounds of potatoes on that raised bed. And of the entire crop, only six potatoes had slug damage.

The miracle continued in 2002. May was warmer and wetter than average in the UK, and not surprisingly, high levels of slugs and snails were reported by many gardeners. In my garden, admittedly, most of the Cosmos disappeared from the flower garden, but I had a bumper spinach crop in the spring. The runner beans survived (minus four) without any fortifications at all. I saw slime trails in the greenhouse, but the tomatoes were completely untouched by molluscs. In June 2002, I passed a personal milestone. I do not throw the snails out of the greenhouse any more.

What is going on? A possible clue lies in the fact that molluscs’ blood contains haemocyanin, based on copper, whereas human blood is based on iron, haemoglobin. I wondered, what effect does this have on a slug’s behaviour?
Perhaps it is thanks to the existence of haemoglobin in our blood that humans are able to think at all. The circulation of the iron in our blood around the body is the anchor of an independent electromagnetic field. Iron can be magnetised, so one piece of iron can hold a different field from another. This property of the iron in our blood allows us to think different thoughts and feel different feelings from the person standing next to us. Even though we live within the Earth’s magnetic field, we have the ability to maintain our own independent field within it.

It would be a very different scenario if our blood were based on haemocyanin. Copper is non-magnetic and highly conductive, so we would have no independent field. Instead, we would be intensely aware of external electromagnetic variations. We would be sensitive to differences in the Earth’s magnetic field in a way that is beyond our imagining, and we would be compelled to respond. We would not be capable of any independent action at all.

Maybe this is what governs the behaviour of slugs and snails. They aren’t attracted by my newly-transplanted lettuce seedlings, but are compelled to respond to the disturbance that has gone on in the soil there. The disturbance may be the residual magnetism from a rusty nail, or the magnetic signature from the iron tool which turned the soil. This is what attracts them. When they arrive in the area, they need some sustenance, so they eat my seedlings. If I throw these slugs in the compost bin, the disturbance still exists in the lettuce patch, so they or other slugs and snails will still be attracted to it.

But working the soil with copper tools has the opposite effect. As copper is conductive, it leaves no magnetic residue, but rather it connects up any breaks in the magnetic field. So there is less to attract the slugs and snails. They wander over the area, but don’t stop for long, and so don’t need to eat anything.

This may give a hint to the role of the garden molluscs. If my thinking is correct, then the slugs and snails play a valuable part in the ecology of the garden. They represent the highly conductive metal, copper, roaming around the garden, rather like those robot lawnmowers that are supposed to keep the lawn trimmed. They help the land to link up with itself, by smoothing out any disruptions in the flow of the geomagnetic field. The slime trail is their visiting card. So in my garden, I now leave them to do their job.

I am not academically trained in any of the areas touched by these speculations, and would appreciate any comments or feedback from those who are. I can’t explain the survival value of this behaviour to the slugs and snails, for example. It is also undeniable that they do seem to target certain plants, which is another area worth investigating. They must be responding to extremely small variations in the geomagnetic field, but that also seems plausible. After all, Homeopathy also works with scientifically insignificant quantities. In the meantime, I am delighted that the slugs and snails do not devastate my garden any more.

Jane Cobbald