I don’t think it is possible to separate Macraia liturata and signaria as a caterpillar… well at least not if the photo’s at Lepiforum.de and Ukleps.org are all correctly identified. I have beaten three caterpillars ex Picea abies in Luxemburg, Nommern, August 22, 2019 and wonder if they are all liturata or a mix of liturata and signaria. Head seems to be variable and also the coloration of the prolegs (more reddish in liturata?). The subdorsal lines seem to be more obvious in liturata…… Well I photographed all caterpillars multiple times and will rear them ….. Quite interested in your opinion.
All the best,