Nettles support over forty species of insects and the peacock, red admiral, comma and small tortoiseshell butterflies all rely on them for feeding and breeding. Matthew Oates ("Garden plants for butterflies") recommends that to attract butterflies to breed a nettle patch should be at least nine feet by three feet and be in a warm and sunny spot. He also recommends that as the small tortoiseshell favours laying her eggs on young nettles then the most southerly third of the patch should be cut down to the ground in the second week of June - the first brood of caterpillars will have dispersed by then and the immediate regrowth will be utilized by females laying eggs in late June in early July.
The red admiral caterpiller folds a leaf together to make 'tent' securing the edges with silk. Within this structure the young caterpillar can feed in relative safety:
Not only are nettles great for wildlife they also make a great compost activator and you can eat them. So be nice to nettles.