Megalomyrmex acauna is a Neotropical species of ants in the subfamily Myrmicinae. Known from Brazil and Peru. It is similar to M. leoninus-group. Its head width (HW) is 1.45âÂÂ1.63 mm and head length (HL) is 1.68âÂÂ1.75 mm. Its scapus length (SL) is 2.13âÂÂ2.28 mm.