The common blue is the UK's most widespread blue butterfly, found wherever its larval foodplant bird's-foot trefoil grows. Despite its name, it has declined with the loss of unimproved grassland.
Common blue welfare depends entirely on the availability of bird's-foot trefoil in short, warm, sunny grassland. Improved grassland management that eliminates wildflowers and replaces them with ryegrass monocultures removes the larval foodplant. Roadside verges, chalk downland and brownfield sites now support important common blue populations. Verge management that includes a single late cut after butterfly egg-laying and larval development (August-September) maintains suitable sward height while allowing foodplant persistence. Gardens that allow patches of lawn to grow unmown until autumn can support common blue oviposition if bird's-foot trefoil is present.