The scale of the dataset reflects a huge public effort. Volunteers have walked more than 932,000 miles in total at more than 7,600 sites
“Without this evidence timeline, we would be flying blind,” said Steve Wilkinson, director of the Joint Nature Conservation Committee which advises the four UK governments and helps run the UKBMS.
“Understanding where conservation efforts are making a real difference and where we need to strengthen efforts, depends entirely on the quality and continuity of data that our volunteers make possible,” he said.
Much of the conservation effort is focused on protecting and enlarging the habitats butterflies need to survive, particularly in the face of land-use changes, including the intensification of farming and environmental degradation.
It is made even more challenging because of how picky some butterfly species and their caterpillars are about what they eat.
Many species have evolved to rely exclusively on one or two specific plant species for food – the Duke of Burgundy on primroses and cowslips, for example, or the purple emperor on goat or grey willow.