Monday, May 26, 2014

Slug Wars Chapter 1: Making DIY Electric Slug Fence Review

Continuing on the identity crisis remark, I am now in the critical identity development phase of seeking enemies to wage war against. Slimy, ugly creatures which steal and eat our food while we are not watching seemed like a perfectly good deal for engagement. This is Chapter 1 of the long Epic Saga Of Slug Wars, which begins here and now, and possibly ends, also here, and now.

You can use this review to build your own electric slug fence. Feel free to comment below on your own versions or visions of the fence. You don't need to comment the electric fence on this review, if you absolutely don't need to.

Why on earth would I make an ELECTRIC FENCE against slugs? 

Well, firstly, because I realized that I can, and it sounded like a marvellously cool thing to do. Secondly, because none of the other slug-repellent methods don't really work (coffee leftovers, egg shells, ashes, marigold, whatever, screw it, I like the first reason for making this thing better). And, oh, it is pretty cheap also.

The Final Product: Electric Slug/Snail Fence. No Snail Shall Pass.

Electric Slug Fence: Proof of concept

Watch this video which shows the effectiveness of the DIY fence with simple example: two copper wires are connected to a 9V battery in an open circuit. When the snail touches both of the wires, it closes the circuit, gets shocked, and retracts.

Electric Slug Fence: How Does it Work?

The basic principle behind the DIY electric fence against slugs is this:
Slugs don't like being shocked by electricity.

9V battery (other batteries might also work)

As I've previously stated, two copper wires are connected to a 9V battery in an open circuit (wires are not connected together in any part of the fence). When the snail touches both of the wires, it closes the electric circuit, and because the slug is conductive, the electricity starts to flow through its body. Apparently the slug does not like this feeling.

For the construction of the fence, I needed only this:
  1. Insulated copper wire (you can get these in electrical supply stores. Don't forget to mention why you need it! It will be fun. For a random bystander, anyway). Of course, first you need to determine wire length that you require for the project: measure the area around which you plan to install it, and multiply this by 2 (you need 2 parallel wires for an open circuit). Add about 5-10% on this number for potential f***ups. I think the cost was below 0.1$ per wire meter, but not sure.
  2. Wooden planks, or something else, onto which you will be able to fixate the wires to. 
  3. 9V Battery and an appropriate adapter.
  4. Insulated weather-proof box for battery containment. You can also get these in electrical supply stores. About 3$. 
  5. A stapler.
  6. Staples.
And this:
  1. Other things.

Electric Slug Fence: Pretty Pictures

0. Insulated copper wire for the electric fence. This is the wire leftover from the fence described in this article. Altogether cost for the wire was about 10$, and there is still enough wire left for another fence of similar dimensions.

1. We were planning to replace old wooden ceiling planks, which gave me enough "free" materials for electric fence construction 

2. Material management at its best: throwing the planks out of the window, near the construction site. They broke a little.

3. Setting up the planks around garden bed

4. First attempts to stamp the wires to planks with 3$ worth stapler ended rather miserably for the stapler. This was also the end of day 1 of the fence instalment because I had no other stapler nearby. Moral of the story: with greatly low price comes great responsibility. And lots of cursing. 

5. Day 2 of the fence instalment started with a fresh new tool and unending doubts about whether I bought the right-sized staples.  

What you need is two parallel wires running along one another, one attached to positive "+" side of the battery, and the other attached to the negative "-" side of the battery. These parallel wires are not connected together (they are not touching, they are not short-circuited, nor connected together via any other consumer) in any part of the fence - the electrical circuit must be open by default. When slug is approaching, he first touches the first wire - nothing happens. As he crawls further, undoubtful in his malevolent plan to eat your juicy salad, he touches the second wire, aaaaand - gets shocked. By touching the other wire, the beast from hell closes the electrical circuit, retracts, and begins to contemplate upon its original evil plans.

6. Stapled wires. I had to gently hammer each staple a bit, for a more tight fitting. 

7. Removing the insulation from the top of the wires.

8. Like a pro. Wires are insulated from the wood in case the planks get wet and conductive. Also, they are insulated from the staples, which are again connected to the wood and could close the circuit in certain conditions, but not in this case. How long this took? It took some time, yes. Especially considering that you have to navigate around all the vegetables and trying not to kill your food.

9. Drilled two holes on the weather-proof (3$) box for the wires. The 9V battery should be safe and cozy inside.

10. Like a pro. So in the meantime, I lost the 9V battery adapter, which I have been keeping safe especially for this project. But, there was no way to end the day before plugging the fence to some electricity. And this was the result of the pure enthusiasm. 

11. It is alliiiiveeeeee!

12. Day 3 started with accidental finding of two 9V battery adapters, which were in my wallet the whole time. When I say the whole time, I mean they were in my pocket while I was connecting the battery the first time, wondering where the hell did I put them.

In all our experiments previous to making this larger-scale fence, none of the slugs were able to cross the fence. Ever. Well, four times to be more precise, as this is the number of experiments we were conducting. Also, none of the slugs died - they just retracted when touching the other wire/closing the electric circuit (watch the video).

Making DIY Electric Slug Fence THE GOOD

  1. A method which effectiveness is proven in the real world, using scientific experiments. Well, ... experiments.
  2. Easy to build.
  3. Cheap.
  4. It is an ELECTRIC FENCE! What more reasons for building it there need to be?

Making DIY Electric Slug Fence THE BAD

  1. It needs to be made by physical work and stuff.
  2. The ground is often not complying with the flatness of the wooden planks. My recommendation is that you cut the planks into smaller pieces so they fit the ground more easily - this is far less excruciating than trying to even the ground below planks, believe me.
  3. About the non-killing part... hm, well, sometimes when a slug can't cross the fence, it dies on it due to a extremely sunny weather, and because it did not manage to reverse and hide in time. Because it is touching both wires at this time, the circuit is closed and it is draining the battery (not significantly, but it can be measured).
  4. Because of the same reason, you need to clean the wires and contacts occasionally. But this is really low-maintenance, all it takes is a few seconds to restore it to factory conditions.


  1. I have come up with a similar idea independently--first using a 6 volt, 4.5 AH and then a 12 volt, 8.5 volt, 8.5 AH battery with a 220 ohm drop down resistor and then no resistor at all. My investigation leads me to believe that this is only minimally effective for two reasons.
    Number one is that the slug himself has a very high resistance of about
    216 K ohms, so the current generated when he shorts the electrodes is a very minimal 5 to 6 MICRO amps, not enough to kill anything.
    Number two, is that the slime the slug generates from being zapped shorts the electrodes with about a resistance of 400K ohms and at the same time corrodes the copper conductors.
    Knowing that the slugs are nocturnal feeders, you'd be better off comming with a flashlight and a small plastic bag after 9 pm for a few days and picking all the slugs you can spot.

    1. Well dear Sir, you have certainly deserved a cookie for this comment. I like it - specific values, experiments, critical approach, valuable information.

      Although the method certainly has some shortfalls, I have to say, I am satisfied with the results in our case. The shock does not kill them - but they are stupid enough to try again and again until the sun fries them. The fence was on about a whole year, and it was still functional - with the same 9V battery! The resistance value of the slug came as an advantage in this case.

      I have some modifications in mind, and will try to encompass the whole garden this year, which is about 100m2. I will update on the results.

      The war is on, their number is vast, and the electric fence is just one of the many battle methods that we utilize. We are still picking them, drowning them, salt them, stab them, and are even thinking about getting the ducks to eat them. The method depends on characteristics and the priority of the location.

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  3. Interesting. Have you modified your approach somewhat? I'm thinking about building one in our garden, but will probably have the electric fence on vertical standing planks.

    1. Indeed I have! Vertical planks, non-insulated cheap steel wire, construction foil under the planks. More details soon in the new Slug Wars post.

  4. great work!
    have you done the v2? I have heard that putting them horizontal can cause short ciurcuit. Have you experienced any? (or maybe the fact that you kept the wire insulated on the ground side solved the issue?)

    1. Thx!
      Yes, I made v2, just had no time to write an article about it - yet. No short circuits occured (well, if you don't count the complete flooding of the "water tight" battery housing), and this time I didn't even bother with the insulated wire, just the bare cheap one.