Thanks so much for all of the excellent advice. I think my conclusion is that we will avoid nettles then as it doesn't seem worthwhile. Just trying to include everything I can to help them along, but at the same time don't want an invasion of nettles.
If you want to grow a food plant for caterpillars why not grow Hedge Garlic/Jack by the Hedge http://www.wildfooduk.com/hedgerow-food-guide/hedge-garlic-hedgerow/ - it's pretty and not too invasive and you can eat it ....... and it's the food plant for the caterpillars of the Orange-tip butterfly - one of the first signs of spring
Thanks Dovefromabove. That certainly looks an interesting choice, and preferable to stingers.
"If you want to grow a food plant for caterpillars why not grow Hedge Garlic"
Good advice. Not in pots obviously, but it should self-seed around the garden in the weedier areas. We have quite a lot in the garden here naturally. Orange-tip eggs/caterpillars are generally present on quite a high percentage of the plants, and are very easy to find.
Where can I get nettles that I can grow in my garden? For caterpillars
Just do nothing to an area of ground. They'll arrive! The problem is stopping them!