7 September 2020

7 September 2020 – Is this a Dagger which I see…?

Grey Dagger [larva] (Acronicta psi)

Clearly visible on the leaf of an apple tree was a caterpillar of distinction.  Short black hairs, a line the colour of confectioner’s custard down the back, several red stripes on the side of each segment of the body and a white line above the feet. The fourth segment of the body has ‘an erect, elongated, black conical protuberance’ and there is a shorter tuft on the twelfth segment. 

Perhaps it is immune from attack from the usual predators?  It seemed to be in no particular rush to hide itself beneath the foliage as it gently undulated its way along the upper surfaces of the leaf.  

Grey Dagger (caterpillar illustration)

British Moths and their Transformations

provides an accurate drawing of the creature and identifies it as the larva of the Grey Dagger (Acronicta psi).  When this caterpillar pupates, and eventually emerges as an adult, it will have a doppelganger in the form of the Dark Dagger (Acronicta tridens). When compared the two moths appear to be exact copies of each other and only dissection will determine which species is which.  The caterpillars are markedly different, however, so train your eyes to search among the hawthorn or the dog rose or the apple and one or other might be discovered.  

The Daggers are very common and carry dagger markings on their forewings as well as the mark psi (Ψ) the twenty-third letter of the Greek alphabet; acronicta is from the Greek ‘akronux’ meaning ‘nightfall’.

Grey Dagger: illus (Acronicta psi)

 Which Dagger is this I see before me?