This large-sized moth has long, narrow, rounded, brown-grey forewings which can vary enormously in the ground colouring and marbling. The orange-yellow hind wings, from which it gets its name, have a narrow black band along the rear border and are strikingly colourful when in flight.

Behaviour

This moth is found in a variety of habitats but favours open grassy lowlands. The large yellow underwing is a night-flying moth attracted to lights and sugary substances. During the day, when the moth is at rest, the wings are slightly overlapped thus obscuring the bright orange-yellow underwings. In fact, the yellow underwing is rarely visible except for short glimpses while in flight.

The larvae can be found from August to early spring, but are difficult to see as they feed at night and hide underground during the day. The caterpillar’s food plants cover a wide range of herbaceous plants and grasses including docks, marigolds, foxglove and annual meadow grass. The caterpillar over-winters and pupation takes place just below the surface of the soil between May and July when the dark, ruby red pupae are exposed, often by gardeners. The adult emerges ten to twenty days later.

Size

• Wingspan: 42-55mm

Status

Common and widespread; of no concern

Distribution

This moth is widespread in the British Isles both as a resident and migrant. It is possibly the most abundant moth found in the British Isles. It can be found, in abundance across Scotland including the Northern and Western Isles.

When to see

Adults fly from June right through to October, with a peak in August.

Facts

• The forewings of males have a ‘marbled appearance’, whilst females seem almost uniformly coloured mid-brown or grey-brown. A small black tick mark near the tip of the forewings is perhaps the most consistent feature.
• There are six similar species of yellow underwing moth in the UK which are difficult to tell apart, sometimes requiring examination under a microscope. Most are smaller than the large yellow underwing and include the broad-bordered, lesser broad bordered and least yellow underwing, as well as the much rarer lunar yellow underwing. The latter is more common in Southern England and infrequent in Scotland and Northern England.