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A beer trap?....what is that? My egg shells are going into my compost heap and i don't think i will have enough for around the greenhouse and my planters 😭

Ask everyone you know for shells basically!

As for the beer, get some of supermarkets ownbrand, dig a hole, place beer glass in, fill with beer. Slugs are allured to the beer and sadly drown but are probably very drunk before that. One saving grace