How to anti-slug fence to prevent Rat Lung Disease (Angiostrongyliasis)

Angiostrongylus cantonensis is a parasitic nematode (roundworm) that causes Rat Lung Disease (Angiostrongyliasis), the most common cause of eosinophilic meningitis in Southeast Asia and the Pacific Basin. The nematode commonly resides in the pulmonary arteries of rats, giving it the nickname the rat lungworm. Snails are the primary intermediate hosts, where larvae develop until they are infective.

This fence is used all over the world, but it is especially important here on the Big Island of Hawaii because of the high incidence of Rat-Lung disease in the Puna area which is spread by the slugs here.

I first learned about the electric slug fence by watching the following video on You tube, so I would suggest you start by watching it.  I will then go on to show you how I adapted this concept to my own needs, which you can do too.

Here’s how I adapted the information in the above video to my situation,  and once you understand the basic concept of this fence, you can adapt it to your situation too.

Cross section of anti-slug fence
Cross section of anti-slug fence

I built my slug fence by using 2″ x 8′ strips of PVC board (available at the Home Depot).  The above picture shows a cross section of how it is constructed. The bottom board rests on the ground, so the PVC won’t rust or rot. Then a second board is put on top, sandwiching a piece of tarp. The tarp keeps slugs from coming up out of the ground and getting into your garden containers. Then, a second PVC board is attached on top and secured with a 1 – 1/4″ deck screw. The boards are overlapped at the corners for strength.  On top of the top board, I put two rows of copper wire which are attached to a 9 volt battery.

The next picture shows how it looks when completed:

So I made an 8′ long by 2′ wide frame of PVC boards sandwiching a tarp as described above. Inside this square I had room to place four 20 gallon grow bags to grow my lettuce and kale, and now slugs can’t get to them.


This picture shows how I connected a battery to the two copper wires running on top of the top PVC board. In this photo I used a 12 volt battery, which I found is too much voltage. The problem with too high a voltage is that it kills the slugs and then you have to clean them off your wires. I have since switched to a 9 volt battery and like the video above says, it is enough to make the slugs turn around.

For wires, I used 24 gauge copper wires, with copper plated nails ( get copper plated nails at HPM building supplies in Hilo).  You can also use stainless steel wire and SS screws too, though I find SS wire is very stiff and copper is softer and easier to work with. The reason I use the same type of metal fasteners and wire is to avoid galvanic corrosion which occurs when dissimilar metals are used and there is electric current present, so it is important to use the same type of metals. I used copper because it is a better conductor than SS, although for this small a fence is shouldn’t be that big a difference. (Pure copper oxidizes, but only on the surface in the form of a dark green patina. Like paint, this coating of oxidation  prevents any further oxidation.  This surface oxidation does not weaken the copper or reduce electrical conductivity). (note: after several weeks I found that the copper plated nails from HPM will rust if exposed to water. It appears that the copper plating is not very thick.)

So, if your slug fence is always dry, like inside a greenhouse, then copper may be fine. If it is at all exposed to the rain, I suggest using stainless steel. Stainless steel wire can be bought locally in a small roll at ACE hardware stores,  Ben Franklin store in Hilo, or purchased in 100 or 200 yard rolls from  which sells it as fishing line. I suggest getting the 12 lb. test line.  The wire from Buck Perry is the least expensive, even with the postage.  A customer told me that SS wire is difficult to solder though, so plan on using crimp connectors for SS wire.

Update: I bought the Stainless steel wire from and I had a problem with it: it kept breaking for no reason that I could see. So, I decided to break the rule of using dissimilar metals and I’m now using SS screws with copper wire. So far it’s working. No sign of corrosion and no mysterious breaking of wires.

In mounting the wire, I put nails in every 10″ or so, and wrapped the wire once around each nail. It is important to make the 2 strands of wire as close as possible without touching each other because some slugs are small and may not contact both wires at the same time if they are too far apart, and some slugs will enter at an angle reducing their overall length. About 1/2″ is practical, but it will depend upon your ability too.

To make a connector to attach the fence wires to a 9 volt battery, you can take the top off an old 9 volt battery and solder wires to that, then you have an adapter that snaps right on to a 9 volt battery making it easy to change batteries. If you’d rather buy a ready made connector, I used to get them at Radio Shack at the mall in Hilo, but they went out of business, so now you can find many of them on Ebay – just search for “9 volt battery connector.”

How long should a 9 volt battery last? Quite a long time because there is really no load on the battery. The wires are really just an extension of the battery. But, if something falls on the wires and shorts them out, it will draw down the battery. The same can happen if the wires get wet for prolonged periods of time.

If you want to see my sample fence in the picture, or ask questions about this fence, or have me give a presentation to your group about this project, contact me, or come by the Maku’u farmers market every Sunday from 8 am to 2 pm. I”m in booth A7.

Here’s another video showing the effectiveness of the slug fence:

Why it is important to grow your own fresh greens

In her book, “Beyond Organic . . .  Growing for maximum Nutrition,” author Jana Bogs says:

“. . . even organic foods have little more nutrient density than those conventionally grown.”

” Learn how the Beyond Organic Growing system can produce Nutrition Grown foods with many times the nutrient content of typical produce. Plants must receive the optimal nutrition they need to express their full potentials to create large arrays of health-giving phyto-nutrients. In turn, people and animals who eat these Nutrition Grown plants receive thousands of phyto-nutrients they need to help them express their full potentials.”

It is my opinion that home grown produce has a higher nutrient content than any produce you can buy, for several reasons. You can pick it and eat it in less than 30 minutes or so, whereas  produce you buy may have been picked several days ago, and once it is picked, it gradually loses nutritional content.

For instance, take vitamin B12. A natural doctor friend of mine once told me that this vitamin is abundant in nature – you don’t see animals eating B12 tablets, do you? So if it is so abundant, why do so many people lack this important vitamin? Because, he told me, it is because this doesn’t last more than 20 minutes or so on the plant after it is picked. And if you observe the animals in nature, such as cows, this seems to make sense.  They are eating freshly grown plants, not plants that have been picked, transported hundreds or thousands of miles, and refrigerated  for several days before being eaten, all the while losing nutritional content.

Also important – keep your rat population down – see the Rat Control page on this website for how to do this.

Another Important point to prevent Rat/Lung disease – keep slugs out of your irrigation water

After you go through all the time to build a slug fence and eradicate rats, there’s one more way to catch the disease: slugs can get in your irrigation water and when you water your greens you’re sprinkling your plants with water containing slug stuff.

I’ve found slugs in my watering cans. So now I keep the cans inside the greenhouse at night protected by my anti-slug fence.

If you water with catchment water, it should be protected from slugs getting in it. Cover the tanks securely with screen so slugs, frogs and other critters can’t get in.

You can also filter your irrigation water.  I recommend the Doulton Ceramic filter.  Here are some specs on it:

Big Blue type ceramic module for whole house 0.9 microns absolute filtration rating as defined >99.99% efficiency.

Big Blue type ceramic module for whole houseMost efficient system for cysts removal compare to any available alternative technologies such as chlorine, ozone, UV, RO etc..

Read more about the Doulton water filter at: