[2] Queens are known for R. admixta, R. diminuta, R. notorthotenes, R. peregrina, and R. shuckardi, plus two unassociated forms.

[2] The species included in this genus exhibit a habitus that is convergent on some groups of Monomorium.

In his study of the Afrotropical members of that genus Bolton (1987) noted two indeterminate Madagascan species which had a high palp formula (5,3), the highest attributed to Monomorium, but did no further analysis of these odd species because the focus of the survey was the extensive Afrotropical fauna.

Heterick (2006), in his revision of the Malagasy species of Monomorium, recognised the peculiarity of the high palp formula and utilised it, together with some other characters, to define his M. shuckardi group, all members of which are now transferred to Royidris.

No unambiguous apomorphy can be stated for Royidris, and in fact its habitus is similar to that commonly seen in Monomorium.