Evening bats are dark brown except for their black ears. There is no hair on the snout, wings, or tail membranes (Kurta, 2001).
Evening bats weigh between 6 and 14 g. The body is 86 to 105 mm long, and the tail is 33 to 42 mm long. Evening bats have a wingspan of 260 to 280 mm. The hind food can be between 8 and 10 mm long, and the ears are 11 to 15 mm in height. The forearm is 34 to 38 mm long.
Evening bats are sometimes confused with Myotis species, although evening bats have a curved tragus not seen in Myotis. Evening bats can also be confused with Eptesicus fuscus, although E. fuscus is larger (39 to 54 mm forearm) and has a keel on the calcar (Barbour and Davis, 1974) while Nycticeius humeralis has no keel. (Barbour and Davis, 1974; Kurta, 2001)
Evening bats are found in the southeastern part of the United States. They are found from Virginia and North Carolina as far west as eastern Texas and as far south as Florida. There is one record of an evening bat in Ontario, and three records from southern Michigan (Kurta, 2001). (Kurta, 2001)
Evening bats prefer the forest and open habitats such as river corridors and wetlands. These are forest bats and are never found in caves. Instead N. humeralis roosts in hollows of trees, under loose bark, or in buildings. (Kurta, 2001) (Kurta, 2001)
One male mates with up to 20 females. Males and females then go their separate ways. Females give birth in colonies with other females, but no adult males are present (Nowak, 1999). (Nowak, 1999)
Evening bats mate in the late summer and early fall, but they don't get pregnant until spring. Females store sperm in their reproductive tract until spring, when ovulation and fertilization occur.
Adult male evening bats may have a harem with about twenty females. The young are born in nursery colonies in hollow trees, behind loose bark, or sometimes in buildings and attics. Females usually have twins, can have triplets and successfully raise them. The pups weigh 2 g and birth. This is half of the mother's weight after giving birth. This makes evening bat pups one of the largest newborn mammals compared to the size of the mother (Kurta, 2001).
Pups are pink and hairless at birth, but they can squeak. They open their eyes within 24 to 30 hours of birth. Young evening bats don't fly until they are about three weeks old. The pups are weaned 6 to 9 weeks after birth. Males leave the roost after six weeks, but females remain in the colony in which they were born. Bats breed in the year after their birth (Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001; Nowak, 1999)
Young are born naked and blind, but they develop rapidly. Pups are able to fly by the end of three weeks. Females nurse their pups for about six weeks, and provide all the parental care the young bat receives. However, there are reports of communal nursing in nursery colonies. A mother recognizes her pups within the colonly by their smell and their voices. If any of her pups fall before the are able to fly, the mother will fetch them. Male pups leave their home at 6 weeks of age, but female offspring remain in the colony of their birth for the rest of their lives (Barbour and Davis, 1974; Kurta, 2001). (Barbour and Davis, 1974; Kurta, 2001; Nowak, 1999)
Most evening bats are expected to live about 2 years in the wild, although some have been known to live as long as 5 years (Nowak, 1999). (Nowak, 1999)
Evening bats live in groups. They roost in colonies of around 30 bats. In October, females living in northern populations migrate south, as far as 547 km. In the spring, females return to their northern homes to have their young. Males do not migrate with the females. Instead, they stay in the southern portion of the range throughout the year. (Kunz, 1999; Kurta, 2001; Watkins, et al., 1972)
There are no data available on the size of home ranges for these animals.
Not much is known about communication in evening bats. Mothers use the voice of the pup and its scent to locate it. Touching may be important in the roost, where animals are likely to come into contact. Touchiing may also be important in the communication between mates, and between mothers and their young. Like other bats that eat insects, evening bats use echolocation to find prey. Visual signals are probably not used, since these animals have poor vision and are awake only in the dim light of night. (Kurta, 2001; Nowak, 1999)
Evening bats eat beetles, moths, flies, and leafhoppers that they catch in midair. While hunting, these bats use slow, steady flight. When a batthat is hunting alone cannot find prey, it will follow a group of bats to the food source. A colony of 100 bats can eat over 1.25 million insects a season! Evening bats find food using echolocation. (Kurta, 2001)
Because evening bats eat so many insects, they probably play an important part in regulating insect populations. By eating these insects, they have a positive effect on the plants that the insects feed upon.
Some bats roost in buildings and attics and are a nuisance to people. They can carry rabies, which can be transmitted to humans that are bitten by an infected bat.
Evening bats feed on the adult form of a chrysomelid beetle, better known to farmers in its larval stage as the corn rootworm, which is an agricultural pest. By reducing the numbers of these pests, evening bats may increase the yield of the harvest.
It is likely that the conversion of forested wetlands to agricultural and logging uses has resulted in prime foraging and roosting habitat.
Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Nycticeius humeralis mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)
Nancy Shefferly (editor), Animal Diversity Web.
Melissa Neely (author), University of Wisconsin-Stevens Point, Chris Yahnke (editor), University of Wisconsin-Stevens Point.
Barbour, R., W. Davis. 1974. Mammals of Kentucky. Kentucky: The University Press of Kentucky.
Cryan, P. 2010. "White-nose syndrome threatens the survival of hibernating bats in North America" (On-line). U.S. Geological Survey, Fort Collins Science Center. Accessed September 16, 2010 at http://www.fort.usgs.gov/WNS/.
Kunz, T. 1999. Evening bat| Nycticeitius humeralis . Pp. 117-118 in D Wilson, S Ruff, eds. The Smithsoninan Book of North American Mammals. Washington, D.C.: The Smithsoninan Institution Press in Association with the American Society of Mammalogists.
Kurta, A. 2001. Mammals of the Great Lakes Region. Ann Arbor, Michigan: The University of Michigan Press.
National Park Service, Wildlife Health Center, 2010. "White-nose syndrome" (On-line). National Park Service, Wildlife Health. Accessed September 16, 2010 at http://www.nature.nps.gov/biology/wildlifehealth/White_Nose_Syndrome.cfm.
Nowak, R. 1999. Walker's Mammals of the World, Sixth Edition. Baltimore and London: The Johns Hopkins University Press.
Watkins, L., K. Jones, H. Genoways. 1972. Bats of Jalisco, Mexico. Special Publication Mus. Texas Tech University: 44.