Stål (1870a) did not give a formal description of this species. He indicated that there were two species, a smaller and a larger one, that were often confused in various museums. He gave characters for separating the two species, and indicated that one was Eusthenes cupreus (Westwood). The other he conditionally gave the name Eusthenes theseus, but he did not indicate any specific specimens examined. The descriptive notes are sufficient, however, to validate this species. Subsequently, it was shown that E. cupreus is the larger species, and so the name E. theseus remained for the smaller one.