While this research hasn’t shed any light on what you can do to obstruct slugs and snails, it has at least shown that these barriers can be unreliableand ineffective. In the case of the snail we have the copper, and the electrolyte in the form of slug slime.The second electrode is missing. Also missing is the connection between the two electrodes which allows the current to flow. I don’t believe that putting slime onto copper will produce an electric charge. Does Copper Repel Slugs?

As existing lab studies have shown some of the barriers work, and as other experiments by Hayley hinted that copper tape could be effective, she’s not ruling the barriers out completely. She hopes to run the study again ona different slug population and different soil type at RHS Garden, Harlow Carr in 2019. Jeff Gillman, one of the Garden Professors, commented “When I’ve tested copper the slugs seemed to have a slight preference for not crossing it, but would if that was what they need to do to get where they were going. I’d call it a mild repellant” . I think this is a good summary. Slugs will not go out of their way to cross copper in tape form, but it is not a fool proof solution. The attention to detail in this study, and the use of the leaf area meter, lets us be more precise and confident in the results." What’s next for slug and snail research?

Why Does Copper Work?

The green patina developed on copper metal over time is a copper carbonate salt and could be toxic. The RHS also plans to test alternative control methods, such as beer traps, and is currently working with BASF to investigate ways to combine scientifically proven control methods into pest management strategies. Help us do more research As members of the Mollusca group of animals, slugs and snails use Hemocyanin proteins in their blood to transport oxygen around their bodies ( whereas we mammals use iron based Hemoglobin). These Hemocyanin proteins contain two copper atoms. This makes all molluscs very sensitive to the ingestion of additional quantities of copper. Too much copper and it prevents oxygen from moving around their bodies and they eventually die, unless they flee to safety. If I go out at night I will usually see 2-3 slugs oozing circles around the bottom of the barrier but not crossing it. I have seen a slug or two successfully cross it, but it’s rare. If I had to guess I would say I get about 1/20th -1/200th the slug prevalence I used to previously high slug traffic areas I have since “protected”. (tough to say because I am too lazy to count, and I can’t tell how many slugs crossed the barrier vs just live on the other side)

My older planters have 6 month old copper mesh barriers and I have yet to notice any obvious decrease in effectiveness with oxidation/dirt, but if there down the road maybe I can mitigate it with a firm wire brush scrub. Lettuces planted in the ground were found to be more susceptible to slugs, with 5.7% of each eaten on average. This compares to just 0.2% of those in pots, which, despite this advantage, yielded less crop. I am not a chemist but guess it is due to some kind of ion exchange or electron donation. My guess is that something similar is taking place between the bright copper and the molluscs. Roofing metals are chosen for the job because their oxides adhere to their surface and are chemically inert under normal atmospheric condition. Knowledge of this fact is what lead me to triy the experiment in the first place. But Dr Hayley Jones, entomologist at the RHS and lead researcher, said: “With the likes of eggshells, barks and mulch so far proving no discernible deterrent to slugs and snails, we would recommend using proven formulas like nematode biological control if the damage is just too much to bear.”Copper DOES work as a slug and snail barrier if the percentage of copper alloy is high enough and the width is in excess of 4 cms. Don’t waste money on any of the other ‘gardening’ products tested above and be cautious of using anything else that comes in a similar sized box ( or from a matching production line…). Encourage their natural predators into your garden by creatinga haven for wildlife, such as birds and frogs.