Similar in general form as M. pharaonisHNS and the body is without erect hairs; clypeus without the medial notch as in M. salomonisHNS . Originally described from the Azores, M. subopacumHNS has been recorded from Antigua in the Lesser Antilles (Kempf, 1972).
Fernández, F. (2007): Two new South American species of Monomorium Mayr with taxonomic notes on the genus. In: Snelling, R. R., Fisher, B. L., Ward, P. S. (Eds): Advances in ant systematics (Hymenoptera: Formicidae): Homage to E. O. Wilson - 50 years of contributions. Memoirs of the American Entomological Institute 80, 128-145: 138-138, URL:http://plazi.org:8080/dspace/handle/10199/15383