Spotlight on The Grey Dagger Acronicta psi

There are two very similar ‘dagger’ species in Britain, the Grey Dagger (Acronicta psi) and the Dark Dagger (Acronicta tridens). The adults cannot be accurately identified visually without genital dissection and microscopic scrutiny – but I don’t like to harm them so this adult would be recorded as an aggregate species Acronicta psi/tridens. The adult is readily attracted to light, and is seen in June and August in most habitats, including woodland, hedgerows and gardens. Sadly its numbers have significantly decreased in recent decades.

The caterpillar is quite an odd thing, and on first discovery I thought it had been parasitised! But the long and prounced ‘hump’ or fleshy projection is one of its defining characteristics and which visually separtes it from the Dark Dagger (Acronicta tridens) which has a shorter ‘hump’. A visually striking moth larva with long hairs and a yellow or white dorsal strip. The orange side patches offer quite a contrast in colouration. It feeds on a large range of broad-leaved trees and shrubs, and overwinters as a pupa amongst bark, in rotten wood or in the ground.

13 thoughts on “Spotlight on The Grey Dagger Acronicta psi

  1. My first thought was akin to yours — what’s wrong with that caterpillar? It’s good to know that the hump is “a feature, not a bug” (as they say)!

    Liked by 1 person

    1. When I first saw it I really thought it was parasitised, as with the hump the caterpillar kind of looked ‘folded’ to me. But I guess that’s the nature of the thing … and that’s nature 🙂


  2. The contrast between larva and adult is amazing in most leps as well as other insects. Some are ugly in both cases and others beautiful on both and some a little of this and a little of that. Love the jets on the adult. I wonder if they aid in flight. 🙂

    Liked by 1 person

    1. The life cycle and differences between larva and adults have always amazed me. Some moth species, their larva feed on roots underground for up to 2 or 3 years before emerging as adults and only surving a few days to mate and ensure future generations.

      Liked by 1 person

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