Head and body length of M. m. molossus is 59-65mm with tail lengths of 30-39mm. Weights range from 10-14g. Upperparts are pale gray brown to dark brown, base of hair is white, with longest rump bristles 8-10mm (not apparent in some individuals). Underparts are gray-brown. Fur is short and velvety, ears are also short and do not extend to nose if laid forward. Antitragus is compressed at the base, circular in shape. The snout is narrow and steeply ridged. Facial skin and ears are brown. Tail length is sligtly more than half the head and body length. Edge of calcar is hairless.

M. m. molossus occurs in dry and semideciduous forest and in towns where it roosts in houses, hollow trees and under palm leaves. More than 300 individuals may roost together between eaves or under corrugated roofs, tolerating extremely high daytime temperatures.

The diet consists mainly of beetles which M. m. molossus forages for after sunset.

Distribution is in Sinaloa and Coahuila (Mexico) to Peru, N Argewntina, Paraguay, Uruguay, Brazil, and Guianas; Greater and Lesser Antilles; Florida Kays (USA); Margarita Isl (Venezuela); Curacao and Bonaire (Netherlands Antilles); Trinidad and Tobago.