This species has the longest ears of any myotis found in Colorado. Black membranes contrast with the medium yellowish-brown fur. The belly is paler than the back. Hairs are lead-gray at their bases. Length averaged 86.4 mm, length of forearm averages 37.6 mm, and weights average 6.1 g. The wingspan is about 275 mm. The only species with which the long-eared myotis might be confused is the fringed myotis, which has shorter, narrower ears and a conspicuous fringe of stiff hairs on the trailing edge of the uropatagium.
Like the Yuma myotis, this species ranges from central Mexico north to British Columbia, but it ranges farther east to the western edge of the Great Plains, including the western Dakotas and Nebraska. This species occurs at moderate elevations throughout the western three- fifths of Colorado, at elevations from 5,000 to 9,800 feet.
The long-eared myotis is a species of coniferous forest, on both sides of the Continental Divide. Ponderosa pine woodland is the most common habitat type, although the animals also range down into piñon-juniper woodland, where they may be abundant. Roosts are in trees (often behind loose bark), caves, abandoned mines and other such sheltered areas. It is possible that the long-eared myotis hibernates in Colorado, as late fall activity has been documented in mines and caves, but individuals never have been found in winter.
Reproduction has not been studied in detail, and dates of breeding are unknown. Males with scrotal testes have been captured in July, August and September. Females form small nursery colonies of one to three dozen individuals. In Colorado, pregnant females are most common in June and July. Lactating females have been captured in June, July and August. A single young is born. Probably, the gestation period is 50 to 60 days, as in other species of myotis of similar size.
The long-eared myotis emerges after dark to forage near trees or over water. The animals are gleaners, hovering to take prey from leaves in forest gaps and edges. Principal food items are moths, flies, spiders and beetles.