An Electric Fence for Snails and Slugs

Anyone with a garden knows about doing battle with pests. Weeds, bugs, rabbits, birds — all of them try to get a bite out of our flowers and vegetables. Some of the worst are mollusks. Snails and slugs are notorious plant attackers. Tomato plants don’t stand a chance when these beasts come to town. Some folks would reach for the pesticide or even the salt, but [wheldot] had a better idea. He built an electric fence to keep these pests at bay.

Much like the electric fences used for large mammals like horses or cows, this fence is designed to deter, but not kill slugs and snails. The design is incredibly simple – two bare wires are strung around the raised garden about one centimeter apart. The wires are connected to a nine-volt battery. No boost circuit, no transistors, just nine volts across two wires. That’s all it takes to turn a slug away.

[Wheldot] didn’t come up with this hack — it’s been around in various forms for years. The nine-volt battery provides just enough current to annoy the slug or snail. The best part is that when not actively shocking a slug, the only current passing through the circuit is the whatever is passed through the wood.

Reddit user [gnichol1986] measured that at around 180 kΩ through wet wood. That means a typical 400 mAh battery would last around 34 days of continuous rain. Even in the UK it doesn’t rain that much. With a little work insulating the wires from the wood, that could be extended to the full shelf life of the battery.

You know, slugs and critters get into electronics too, so don’t forget a waterproof case to make sure your project stays slug free!

73 thoughts on “An Electric Fence for Snails and Slugs

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  2. Can’t you set it up like a touch sensor and then send a high voltage spike through it once a touch is detected? It would use a lot less power that way as the MCU doing the detection can be one of those ultra low power ones with their own touch circuit built in, low enough to work with a small solar panel and battery.. Use a solid state relay to isolate the low voltage detection circuit just before the zap, the return it to detect mode immediately afterwards. Then add the mandatory ESP8266 module for IoT reporting of hits, that stays in sleep mode until the detection MCU wakes it up to send a report.

    1. I would personally isolate the wires by putting them say 1mm off the wood. And isolate them from the staples as well. So now the current flowing through the wood is WAY less. I dare the slugs to limbo beneath that wire…. Ha!

    1. Yup – in fact the local “green” gardening shop sells rolls of copper foil strips with adhesive backing for just this. Snails *hate* it, but it takes a lot to proof your garden beds.

      OTOH, it doesn’t use any energy.

  3. I second the copper tape. Snails and slugs do not cross copper tape. A lot easier.
    And the beer traps are good too. The snails drown happy, then you have to dispose of the bodies or else it gets stinky, where as the copper tape just makes them go and eat someone elses vegies.

          1. Not likely. Slugs actually contain more water per volume than us, but retain about the same mineral content.

            if body fluids and metals were that big a problem, surgical tools would not be made of conductive metals!

  4. Photonicinduction did a version that would actually kill the snails (and anything else living that comes in contact…). Given how little voltage it takes to stun a snail, maybe it’s possible to build a zapper that can kill them yet be safe for people and pets?

    1. Pets are probably more of an issue. They are smaller and probably more susceptible – and humans can read warning signs not to touch the electric wires.
      I would also like the two step approach: detect the slimy critter and let it fly to bits :-) How many joules would be necessary to vaporize a typical sized slug?

      1. Depends on how steep you can make the pulse and how much power you can dump…thick copper conductors, a very low impedance cap bank and even single digits of J would cause destruction…

      1. Ever licked a 9v battery? Sure you notice it plenty with a sort of strong metallic taste sensation that is rather unpleasant, but it’s not that ‘shocking’ really is it? And I guess for a wet dog’s nose it’s the same.

  5. I’ve done this for almost five years now in our garden with aluminum ducting tape and a pair of old, “discharged” 9Vs. They had like 6-7 V on them. Worked for two years on the same batteries.

    Back side of the tape is insulating, so there’s really low leakage current. I couldn’t figure out how to solder to the aluminum tape, so I just taped wires to it. Works fine. Total ingredients: some conductive tape, some 9V clips, some expired 9Vs. Done.

    I watched some slugs try to climb up it. They’d stick their “nose” onto the second piece and turn back. They didn’t like it, but it didn’t seem to do them any harm. The trick is spacing the tapes close enough that no slugs can slip between the gap — they need to make contact with both — but not so close that raindrops short it out.

    Was a fun experiment. It’s still running, but if I had to do it again, I’d probably go copper tape, just because it’s less hassle. Still, I’m stoked to see this on Hackaday!

  6. Nice tricks, so anyone got a working one for birds?

    They keep eating my Cherries, grapes and some other sweet fruits.. And they breach nets also…

    Does this 2 wire trick work with birds?

  7. Nice, these huge snails are becoming a pest in some countries where they were imported as a cheap alternative to escargots. Without a natural predator they multiply without control.

    But these pests will eventually enter your property by climbing trees then falling in the ground.

  8. Not snails, but squirrels.

    Friend of mine had problems with squirrels raiding his bird feeder.

    So, he mounted the bird feeder on a 4×4 post, and ran alternating wires vertically on the post, so the squirrels would contact both of them, with opposite feet. He hooked the wires to the outputs of a fence charger, and put the power switch in his kitchen.

    His wife would be doing the dishes, see a squirrel going up the post, and flip the switch. Then watch the squirrel launch itself horizontally away from the post. He said it was awesome, until all the squirrels learned not to raid that feeder.

    1. I’m amazed at the amount of work a squirrel will do for a snack. I hung my feeder on about 25 feet of that thin chain meant for hanging lamps. Too high to reach from the ground and too far away from the branches. The birds were happy for a week.
      Eventually the rodents figured out how to climb down Mission Impossible style, and then they would scatter the seeds out of the feeder. It was way too far from the ground, so they would have to climb back up the chain again.
      Witnessed one make it to the feeder when it was empty, he sure sounded upset!

      Thoses feeders that close when too much weight is on them only work for about 3 days until the critters figure it out.

    2. Squirrels: live trap, plus a tall trash can full of water. I’m up to 16 so far this year, and am keeping up pretty well with the new ones invading my yard. Squirrels may seem smart, but give them a really tempting bait (I use cashews stuck in peanut butter) and they can’t resist a rather obvious peril. Hint 1: only do this close to your trash collection day (says a guy who learned the hard way). Hint 2: to get your wife on board with this scheme, plant something really nice (e.g., irises) in your garden that squirrels are sure to destroy.

  9. Squirrels and birdfeeders? Flyback transformer, fence charger or microwave transformer? Tiered response maybe. Which still won’t stop the deer or wild turkey from headbutting the feeders to knock out the birdseed.

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