Caterpillars destroying my precious plants!? I live in N Ireland, and pinch great pride in my...

I live in N Ireland, and pinch great pride in my garden, concluding year a lot of my plants be destroyed by green caterpillars, greenfly, or slugs and snails!!
Is there anything apart from penetrating through each fern and squashing the little blighters, that I can get to prevent them, from consumption and destroying everything?
Seeds you can plant within summer contained by...
Answers:    I live in the states, but my mother used to put the rag rolls from toilet paper and tabloid towels around the bottom stem of her plants to keep slugs from getting to them. This probably doesn't oblige with established plants, singular with transplants.

I'm linking to a website within the sources with some other philosophy that would work better for repelling slugs and snails.