Similar to red forms of T. mitchellii but differing in body shape, being inter alia narrower and more straight-sided, with the pronotum more convex and having a proportionately wider coloured area on its margins.

Red forms of T. mitchellii occur on Kangaroo Island (KI) and in the SE Region of SA. In both areas there is intergradation with the more common orange and yellow forms and they appear to be variants within interbreeding populations. This particular red form from Kangaroo Island, however, is more distinctive, and preliminary DNA results indicate affinities with T. mitchellii forms from the Blue Mountains of NSW. There is also evidence (R.V.Glatz, pers. comm., 2017) that it emerges earlier than typical T. mitchellii on KI.

The specimen illustrated here conforms to the original description of Stigmodera karratae by Blackburn 1890b. It also closely matches the two type specimens (with that name) on which Blackburn based his description, and especially the narrower one bearing a label as the Holotype. These two individuals were collected at Karatta on KI by Tepper in November 1886 and are housed at the SA Museum. Further investigation is needed to determine whether this entity warrants status as a separate species.