There is little information on its habitat and ecology. In Paraguay, M. ruber inhabits low semi-deciduous forests (López-González et al. 2001). In Brazil, the species is associated with primary and secondary Atlantic forests, the semi-humid forests of the Caatinga, as well as riparian forests and plantations (Weber et al. 2010). All records strongly suggest that this species occurs in humid woodland habitats, being rare in isolated patches when outside the southern Atlantic Forest. The records outside of the Atlantic Forest, mainly in Pampa and Chaco, were associated with riparian forests, and were indeed near or in transitional areas linking to the Atlantic Forest (Weber et al. 2010). Pregnant females were observed mainly in October in different years (Bernardi et al. 1914). Based on those results, it seems that the species will fit the general pattern for bats determined by climate and food resources, but the data do not allow to assign conclusive reproductive patterns. Known roosts include hollow trees, rocks and crevices in human dwellings.

This species of bat is found in southeastern Brazil, northeastern Argentina, Uruguay, and southeastern Paraguay (López-Gonzalez et al. 2001, Weber et al. 2010, Wilson 2008). The exact geographic location of the single locality in Uruguay is unclear (E. Gonzalez, pers. comm.).

It is found in protected areas in Argentina (R. Barquez and M. Diaz, pers. comm.).