The high brown fritillary used to be a common sight across Wales and England, but its numbers have dropped by 62% since 1970 and it's now one of the rarest butterflies in Britain. The reason this butterfly is in so much trouble comes down to how specific its needs are. Too much bracken chokes the violet out, too little and the ground temperature drops below what the caterpillars can cope with. 'A beautiful obsession'What started as a two-person operation has grown into a group of more than 40, becoming more than just butterflies. "We're a social group – as well as the whole benefit of saving nature and working outdoors," she said.