Although I leave a lot of nettles to grow in my hedge and other wilder areas of the garden I rarely see any catterpillars on them. Just down the road from our house is an expanse of nettles growing under oak and chestnut trees and this week there have been loads of catterpillars on them. These look like the catterpillars of the Small Tortoiseshell butterfly which is one of our more widespread species and we often see it in our garden.