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Saturday, 18 August 2012

Keeping snails and slugs away

A large land snail, found on club moss
under a banyan tree on Tanna, Republic
of Vanuatu on the Pacific Ocean.
A land snail from Margaret River,
Western Australia.
Are you fed up with slugs and snails?

This is a pbi, a partly-baked idea, suitable for somebody looking for a science project.  That means you need to do most of the work!

You can get rid of snails and slugs with bare copper wire, several dry cells (torch batteries—or flashlight batteries if you are American), or a small power pack (transformer-rectifier) and to test it, you will need some live slugs or snails.

Get some advice on connecting the batteries or the power pack to the wires. Look up <electronics components> for local suppliers and enter <battery holder> to find what you need. (That works in Australia, Americans may need to vary that wording.)

Old power packs from discarded phones or other gadgets will do, if they deliver 3 volts or less.

The idea is to make an electric fence to keep snails out of a seedling bed. The best design is two parallel wires, each connected to one terminal of your power supply.

You will need to work on insulating the wires from each other and the ground. I suggest using small pieces of polystyrene foam, cut from waste packaging and pushing the wires through, so as to keep the wires apart and out of contact with the ground.

Questions worth asking:

  • How many volts does it take to repel a snail?
  • What voltage do you need to keep slugs out?
  • If they leave slime across the wires, does this conduct electricity and "flatten" the battery, or waste electricity? 

Some ancient history:

Now here is an old version of the electric fence, based on the way two different metals will generate a small current by forming a "galvanic couple", a sort of simple battery, presented by Septimus Piesse.

It was written up in English and American science journals before the end of 1863, so it is now a very old idea, first published in Scientific American in 1863. The image below comes from that journal.

How to set out the zinc and the copper. 
Scientific American May 2. 1863, p. 276. 
Having a few pet plants which slugs and snails are particularly fond of as food, I have devised the following simple and efficacious mode of protecting them against their and my enemies; and as this plan may be useful to some of your readers, I herewith send you a description of my galvanic circle.

Procure a flat ring of zinc, large enough to encircle the plant; make a slit in the ring after the manner of a keyring, so that it can be put round the stem of the plant and then rest upon the ground.

Now twist a copper wire into a ring very nearly of the same circumference as the flat zinc ring, and putting it round the plant, let it rest upon the zinc, as in the illustration.

No slug or snail will cross that magic circle; they can drag their slimy way upon the zinc well enough, but let them but touch the copper at the same time and they will receive a galvanic shock sufficient to induce them at once to recoil from the barrier.

A bit of simple introspection and research should lead you to the conclusion that the three volts mentioned in my design was massive overkill.

1 comment:

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