The genus Metopiellus (Staphylinidae: Pselaphinae) is confirmed in Colombia. A  new ant-mimetic species of Metopiellus , Metopiellus guanano sp. nov. is described from northern Amazon. Major diagnostic characters and ecological data are given. A new symbiotic association (rove beetle and fungus-growing ants) is hypothesized for the genus Apterostigma (Formicidae: Myrmicinae) and recorded for the first time for the country.