The bat's naked parts of the face, ears, wings, and tail membrane are all black (Kurta and Baker 1990). Some have described it as being "oily" in texture. The ventral fur is lighter, being near pinkish to olive buff. Dorsally, it ranges from pinkish tans to rich chocolates. Pelage color depends on location and subspecies. This bat also has a cartilaginous calcar which articulates with the calacaneum, and has a keel-shaped extension (Baker 1983) The tail is less than half the total body length and the tip projects slightly beyond the uropatagium. The ears are rounded and the tragus is broad with a rounded tip (Baker 1983) The bat's nose is broad and the lips are fleshy the eyes are large and bright. The teeth are sharp, heavy, and were described as capable of causing severe bites. The skull is comparatively large and contains 32 teeth. This species is sexually dimorphic in size, females being slightly larger than males (Kurta and Baker 1990) The wingspan is about 330 mm (13 inches) (Baker 1983). Height of the ears from the notch is 16-20 mm (Kurta 1995). Forearm length is 41-50 mm hindfoot length is 10-14 mm. Total length is 110-130 mm of which the tail is about 38-50 mm. It is reasonable to speculate that populations of the big brown bat have increased with an increasing number of human habitations (Baker 1983). Once inside, it prefers to roost in double walls or boxed-in eaves rather than attics. All this bat needs is a small hole or warped, loose siding to gain entry into a home. The generic name Eptesicus is derived from the Greek, meaning "house flyer".
Recently, some were found hibernating in caves in Minnesota (Knowles 1992). Occasionally groups of these bats are still found living in tree cavities (Baker 1983). In presettlement times it is presumed the big brown bat roosted in tree hollows, natural caves, or openings in rock ledges. Also, this bat has been found roosting in storm sewers, expansion joint spaces in concrete athletic stadiums, and copper mines (Baker 1983). Besides human dwellings, it has been found to take up residence in barns, silos, and churches. Eptesicus fuscus has a more tolerant constitution so it can winter in less substantial structures. Some bats require stable, highly insulated environments in order to hibernate. The big brown bat inhabits cities, towns, and rural areas, but is least commonly found in heavily forested regions (Kurta 1995). Eptesicus fuscus, also known as the Big Brown Bat, ranges from southern Canada, through temperate North America, down through Central America to extreme northern South America, and the West Indies (Nowak 1991).
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