White-tipped Case-bearer Coleophora violacea

Formerly given the vernacular name Violet Case-bearer.

Adults of this species are usually more blackish than this worn individual, so I wasn't expecting this identification (though I wasn't sure what it was). Upon dissection there seemed to be three reasonably strong contenders, sharing a similar length of dense spiculation in the ductus bursae, weakly sclerotised and narrow antrum and large signum: this species, Potentilla Case-bearer Coleophora potentillae and Buckthorn Case-bearer Coleophora ahenella. Working out the differences between these three wasn't easy. Eventually I eliminated potentillae due to subtle differences in the ostium and so was left with a choice between violacea and ahenella. Chris Lewis's British Coleophora website suggested some differences in the shape of the signum, "with a semicircular base plate and medium-length curved spike (shorter than width of base plate" in violacea and "with a fairly flat base plate and a long, fairly straight spike (as long as the width of the base plate)" in ahenella. Mine clearly had a semi-circular base plate as in vioacea but the spike seemed longer than this suggested it should be for violacea. Checking images at the Moth Dissection website and elsewhere I wasn't convinced either were totally reliable, but images of violacea showed a clearly indented centre to the base plate like mine, whereas this was less distinct on ahenella. Furthermore the twisted section of ductus bursae before the corpus bursae was completely crossed-over on mine which matched all the images of violacea (and the plate in MoGBI) but none of the images of either ahenella or potentillae. In MoGBI the densely spiculated section stops closer to the twisted section than it does on the other two species or my specimen, but this does not appear to be consistent. As in the diagrams in MoGBI, all images of ahenella genitalia seem to show a slightly shorter length of dense spiculation than the other two species or mine, which further helps to reassure me that this is adequately eliminated.

One external character supports my identification as violacea, and my elimination of both potentillae and ahenella - the antennae are solidly dark all the way to the tips which are (very indistinctly) white. On both of the other two species the antennae are mostly ringed.

female White-tipped Case-bearer Coleophora violacea showing genitalia, North Elmham (Norfolk, UK), 28th June 2025