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Moth of the Week

Dew Moth

Setina irrorella

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The dew moth is a part of the family Erebidae. It was first described in 1758 by Carl Linnaeus. It is thought to have gotten its common name from how the moth hangs from a blade of grass or a leaf when resting during the day. This gives it a transparent look.

Description This species’s wings can vary in colour from cream to yellow. The forewing has 3 lines of black dots across it with the hindwing usually having only one black dot. The underside of the forewing is gray with a yellow margin. The body is black with yellow or black legs.

There are many found variations of this moth:

signata Borkh. - the middle rows of spots are connected by streaks

ab. fumosa Sandb. - has brownish ground colour; found in the north, but also found in Germany.

flavicans Bdv. - has brighter deep yellow wings and the apex of the abdomen is yellow; found in the Mediterranean and Anterior Asia.

nickerli Rebel - paler yellow, the forewing slightly dulled with the exception of the clearer yellow inner margin; found in the Alps and Northern Europe.

andereggi H.-Schiff. - has dark veins on the forewings, appearing like rays; found in the high Alps, and in the higher North.

riffelensis Fall. - considerably smaller, the ground colour is slightly dulled, the black vein-streaks are more numerous, especially the costa and median veins strongly sooty black; found in the high Alps, especially abundant above Zermatt.

lata Christ. - larger with broader wings and paler with very few markings, the hindwing often quite without markings; found in Russia over North Siberia to Kamtschatka.

insignata Stgr., - quite similar to the preceding, but with narrower wings. The forewing also with very few dots, and hindwing without any; found in East Siberia.

Wingspan Range: 27 – 33 mm (≈1.06 - 1.30 in)

Forewing Range: 11 – 18 mm (≈0.43 - 0.71 in)

Diet and Habitat The larva of this moth eat only lichen.

This moth is found in the Palearctic region. Its range starts from Ireland, then spreads south through Europe and east to northern and Central Asia. It can be found in countries such as Siberia, Kamchatka, Chukotka, and northern Mongolia. This species can even live in the limestone Alps up to 2,000 meters above sea level. However, it can not be found in the high north and parts of the Mediterranean region.

It prefers to live in mossy and lichen-covered rock corridors, on chalky and sandy areas and steep, rocky sparse grasslands, rocky coasts, shingle beaches, and calcareous grassland inland. It can also be found in bogs, forest meadows, and on heaths.

Mating Depending on location, this moth can be seen from May to July. It presumably mates during this time. Generations per year not listed.

Predators Not listed. However, the adult males fly in the afternoon, at dusk, after dark, and at dawn. The females are largely nocturnal. These moths are presumably preyed on by nighttime predators such as bats.

Fun Fact The dew moth has four subspecies:

Setina irrorella irrorella

Setina irrorella freyeri (Nickerl, 1845)

Setina irrorella insignata (Staudinger, 1881)

Setina irrorella mediterranea (Daniel, 1964)

Additionally, dew moth caterpillars do not cocoon in trees or foliage but rather in between stones or rocks.

(Source: Wikipedia, Butterfly Conservation)