This is a large (80 mm wingspan) nocturnal European species which, like most noctuids, is drably coloured to aid concealment during the day. It flies in August and September, and comes freely to both light and sugar.
This species and other Catocala moths have brightly coloured underwings, in this case more orange than red. These are not visible at rest, being hidden by the dull forewings, but they help the moth avoid predators such as birds if it is disturbed during the day.
As the Red underwing moth takes off, the sudden flash of colour may confuse the attacker, and when it lands and immediately closes its wings it may seem to disappear as the colour is "switched off". It is also thought that the symmetrical patterned orange sections on the rear wings form the illusion of another smaller creature (butterfly), so the attacker will go for the colourful "small illusive" rear safe region on the main body of this Red underwing moth species.The adult feeds on nectar, the caterpillars eat willow and poplar leaves.