11 July 2013 - Assassin of the Night.

Our next moth is a special one. It is among one of the larger moth species that is impossible to confidently identify by wing pattern alone. This moth could either be a Dark Dagger (Acronicta tridens) or a Grey Dagger (Acronicta psi), the Grey being more common in Britain than the Dark. The only way to be sure of the moth's identity as an adult is to examine the genitalia. The caterpillars of the two species are quite different, however, and are easy to differentiate. For the purposes of moth recording, groups like Yorkshire Moths only take records of this moth as "Dark Dagger/Grey Dagger" unless measures have been taken to examine the genitalia.

Dark Dagger/Grey Dagger (Acronicta tridens/psi)

The Dark Dagger/Grey Dagger gets its common name from the black dagger-like marks on its wings. Tri- 'three' and dens 'a tooth' mark the three prongs of the Dark Dagger's streaks. In the Grey Dagger, these prongs are described as resembling the Greek letter psi (Ψ). They are very distinct, and in my opinion, make the Dark Dagger and Grey Dagger exceptionally beautiful moths. Moths of the Acronicta genus are night fliers, so akronux 'nightfall' does not accurately describe the habits of the moth, but in conjunction with its ornamental daggers and difficult to distinguish identity, the Dark Dagger/Grey Dagger takes on the air of a twilight assassin.

- Post by Jane Wu