What I think is this. It is often said it is good to leave a few nettles down at the bottom of your garden to encourage the butterflies. Well for a start only a few butterflies lay their eggs on nettles.
More to the point however I do not think there is a shortage of nettles in the countryside. On walks you see masses of them and how often do you see caterpillars like the ones in the photograph? Answer; not very often. If the amount of nettles had anything to do with butterfly populations then we should be inundated with thousands, no, hundreds of thousands of Peacocks, Tortoiseshells, Commas and Red Admirals and are we? No. So leaving a few more nettles at the bottom of the garden is not going to make the slightest bit of difference. You can leave them because you don’t want to get stung but do not kid yourself that you are doing the butterflies a favour.