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Grey Dagger Moth Caterpillar

Scientific Name: Acronicta psi

picture of a Grey Dagger Moth caterpillar

The Grey Dagger moth itself is not as spectacular looking as its caterpillar. It gets its name from the black dagger-shaped markings on its dull grey forewings. The wingspan is from 30 to 40mm and it flies at night from June to August, feeding on nectar. There is a similar moth, the Dark Dagger (A. tridens), though it is usually lighter in shade, but has white hindwings - their caterpillars are very different.

The colourful caterpillars feed on the leaves of Hawthorn, Blackthorn and fruit trees - the one pictured here was found on a Pyracantha bush. Also this example is a later stage instar as it has a broad white stripe along its side and about 40mm in length. They all have a broad yellow stripe along the back and two black 'horns' - one at the rear and a longer one near the front. When disturbed they remain motionless and curl the head under the body raising the front 'horn'. A sparse growth of fine hairs act as another defensive mechanism.
They overwinter as a pupa.

The head is curled under the body when it is disturbed.

The damage caused to leaves is not very noticeable and on a deciduous tree they will shortly be falling off anyway, so there is no need to take any remedial action. Also the adult moths may be important pollinators as they feed.