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. Uniform Application of Copper Sulfate as a Potential Treatment for Controlling Snail Populations in Channel Catfish Production Ponds 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. Of the thousands of enquiries received by RHS Gardening Advice every year, deterring slugs and snails is atop concern. To ensure we aregiving the best advice on this much-debated topic, we set up a project – Gastropod Barriers– to test whether the most commonly recommended home remedies really work. How we tested the barriers 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.”

Encourage their natural predators into your garden by creatinga haven for wildlife, such as birds and frogs. 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? 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. So pleased, daren’t put anything outside, especially with all the rain we’ve had without the tape. We tried it last year for the first time and it really did work. Thanks again. Use this attractive, dual purpose Butterfly House and Feeder to offer butterflies food in the summer and shelter in the winter.…

How we tested the barriers

After tending to the crop for weeks Hayley harvested the lettuces and removed the leaves one by one. She then rated the damage visually and useda leaf area meter for the first time,to record the damage in every square cm of the leaves.

Regardless of exactly why it works, I would recommend copper mesh to anyone with a slug problem amenable to a physical barrier who isn’t too concerned about the aesthetics.Thanks for taking the time to research & test these – very interesting results, and I hadn’t considered the rain factor before.

I have read a few of the articles here. I found you when I was looking up as to why molasses is good for compost. It makes complete sense that when the molasses was all consumed that there would be a starvation problem. Humans energy often crashes when the sugar we consume is burnt up. 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.” Copper pennies and wire do not seem to work. Most products on the market are a type of copper foil or copper tape so this might work better and in fact some people suggest that a wider strip is better than a narrow strip. If you want to protect your plot from slugs and snails, these trialled remedies just won't cut it. You may need to try something different. What can I do?

I imagine barrier efficacy might depend on the width of the barrier and skinnier tapes might be less effective barriers than 5″ of mesh. I have yet to try using any other type of mesh (steel, aluminum) but if I get bored that might be a fun experiment. I also imagine in addition to whatever theoretical chemical/electrical property copper has that slugs don’t like, there is likely a mechanical component because irregular wire loops might be irritating to ooze across and there may be some variability in effect based on the size/configuration of the wire in the mesh. 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. It’s that time of year when slugs and snails creep out of the woodwork ( quite literally) and look for sources of food after their winter hibernation. My alliums are currently being ravaged and I’m out in the garden with a torch at 10pm on most evenings removing the hungry little beasts. Last year I conducted some tests to disprove the value of egg shells, pistachio nut shells, hair and chilli powder in preventing slugs and snails from eating our plants, all were easily crossed by snails. Young chopped brambles were a surprise snail barrier success though.