|White Plume moth Pterophorus pentadactylus|
So, why is it beneficial in gardens? The answer lies in the larva which feeds on the leaves and flowers of bindweeds (Convolvulus spp. & Calystegia spp.) which gardeners otherwise spend a lot of time untangling and uprooting. Personally, I leave it most of the time (it covers some bare areas with greenery) which may be one reason the moth has colonised our garden - plenty of undisturbed food.
If you want to know more about this and other British plume moths, Hart (2011) is excellent, including dissections of genitalia used to separate difficult specimens, and photos of juvenile stages. Well worth getting hold of.
Hart, C. (2011). British Plume Moths. BENHS, Hurst, Reading.