Box tree moth
How to recognise it
Fine webbing among box leaves with green-and-black caterpillars, and rapid, patchy leaf loss leaving bare brown patches.
Life cycle and conditions
Multiple generations possible from spring to autumn in the UK's current climate; caterpillars can overwinter within webbing on the plant.
Prevention
Inspect box plants regularly through the growing season; pheromone traps can help monitor adult activity.
How to treat it
Remove caterpillars and webbing by hand where possible; a biological spray based on Bacillus thuringiensis targets only caterpillars and is the recommended option for heavier infestations, leaving other garden insects unharmed.
Broad-spectrum insecticides aren't recommended here — the Bacillus thuringiensis biological spray above is both more targeted and generally more effective against this specific pest.