Large Yellow Underwing moth and cutworm caterpillar, Noctua pronuba
The Large Yellow Underwing is one of the most common moths to be found throughout much of the British Isles and Europe. In North America its range in recent years has extended as far north as Canada and Alaska.
In many American States they are one of several moth species with larvae referred to as cutworms due to the damage they cause to garden plants and agricultural crops.
In most of its range the Large Yellow Underwing moth flies in a single generation at night between July and September when it can be attracted to light in large numbers both in gardens and open countryside. It also has migratory instincts so resident numbers may also be swollen by the arrival of migrants.
Identification of the Large Yellow Underwing
The Large Yellow Underwing moth derives its name from the yellow hindwings and has a wing length of c 25 mm.
The forewings are variable shades of brown with some exceptionally dark forms.
The pale upper oval and outline of the lower kidney mark is normally evident even on the darkest specimens.
When seen at rest with closed forewings the yellowy orange hind wings with a black sub terminal band are obscured. When disturbed or revealed in flight these underwings appear strikingly colourful.
Scarcer species include Langmaid’s Yellow Underwing and Lunar Yellow Underwing.
Life Cycle of the Large Yellow Underwing
Eggs are laid in large, neatly aligned batches of two to three hundred on the larval food plant. The females will also lay freely in captivity including inside light traps.
Eggs hatch within 10 days and the caterpillars feed on a variety of low herbaceous plants including dandelion, dock, grasses and commercially grown agricultural crops.
As they become larger they feed mostly at night spending the day just below the surface of the soil or amongst the base and roots of plants.
In North America they are considered a species of ‘cutworm’ – larvae that during the day live in the soil and at night bite through stems of young plants and leaves close to the base of the plant before dragging them down into a tunnel in the soil or leaf litter to eat.
Caterpillar of the Large Yellow Underwing
The caterpillars grow to a length of 45mm
Variable shades of brown and green may be found in the same brood.
In late instars a distinctive row of black marks in the sub dorsal region are distinctive features.
The caterpillars overwinter in a penultimate or final instar and may feed sparingly during mild spells.
They are sometimes come across on the ground or even on the surface of snow in the middle of winter.
Despite some over wintering and pre pupating caterpillars losing much of their colour, appearing a pale greenish yellow, the black sub dorsal marks are usually still evident.
Growing commences as the weather warms.
Help with caterpillar identification
Pupating Large Yellow Underwing caterpillar and pupa
Pupation takes place just below the surface of the soil between May and July when the dark red pupae are often exposed by gardeners.
The adult moth emerges in ten to twenty days when they are attracted to light in large numbers and will also feed on sugary substances.
During the day they are frequently disturbed from wood piles.
Rearing the Large Yellow Underwing caterpillar
This species is very easy to rear. Eggs can be obtained from females attracted to light and caterpillars can be easily swept at night in the Spring.