This moth will fly in the daytime but the most obvious indication of its presence in your area is that the tough ubiquitous Senecio jacobaea (Common ragwort) is being eaten to a stump by hordes of stripy caterpillars (RHS photo).

LHS: Garden, Cheshire 20th May 2002 RHS Leasowe Meadows 19th June 2007

Added on November 10th 2004, amended on February 5th 2005, updated 27th June 2008