The evening bat is one of the most common bat species in Missouri. They resemble big brown bats in coloration, but they are smaller and have shorter fur. They mainly inhabit trees but frequently use attics or other undisturbed places in buildings. They do not hibernate in caves.
The general color of the upperparts is dark brown; the bases of the hairs are blackish and the outer portions dark brown. The underparts are slightly paler. The wing and tail membranes, the ears, and the muzzle are blackish.
The ears are thick and almost naked, with rounded tips. The tragus (projection at the base of the ear hole) is broad and curved slightly forward and has a rounded or blunt tip; it is short, less than half the length of the ear. The wing tips are broadly rounded. The wing and tail membranes are thick and almost naked.
Evening bats have a distinct musky odor, which can help identify them.
For your safety and the safety of bats, do not handle bats. Biologists who study bats receive special training and pre-exposure rabies vaccinations. Bats are not aggressive toward people but will bite in self-defense if handled. If you absolutely must handle a bat, wear heavy leather gloves. For more information about bats, see the bats group page.
Similar species: The evening bat is most likely to be confused with the big brown bat, which is very similar in overall appearance (coloration) but is markedly larger: the big brown bat's total adult length (tip of nose to tip of tail) is at least 95 mm (3¾ inches), and the weight is at least 14 g (0.5 oz.). They often reach 127 mm (5 inches) in length and can weigh 31 g (slightly more than 1 ounce).
- Thus the largest evening bats are not larger than the smallest big brown bats.
The evening bat might also be confused with our six species of mouse-eared bats (genus Myotis) and the tricolored bat. However, these species can be distinguished by noting differences in size, color and character of the fur, and shape of the ear and tragus.
Total length: 82–95 mm (3¼–3¾ inches); tail length: 34–41 mm (1⅜–1⅝ inches); weight: 2–14 g (about 0.1–0.5 ounce); ear length: 12–14 mm (about ½ inch).
Statewide. Found throughout most of the eastern United States, excluding the most northern regions.
Habitat and Conservation
The evening bat mainly inhabits trees, but it frequently uses attics or other undisturbed places in buildings. In general, it is a slow, steady flier.
In winter, evening bats tend to use similar roosting sites in trees and habitats. They do not hibernate in caves, but their winter habitat is poorly known. Some individuals overwinter in the same areas where they spend the summer, but others have been recorded migrating up to 340 miles.
During the summer, nursery colonies are formed in cavities or under the bark of dead trees or in houses. Here there may be hundreds of young.
Females show an attachment to the nursery colony and have returned when released 96 miles away. The males do not migrate north in the spring with the females; instead, they remain in the southern latitudes.
When the nights become cool in fall, the bats spend less time away from the roost. They accumulate fat in autumn in order to migrate possibly hundreds of miles, hibernate, or both. In the more southern reaches of their range, evening bats may be active year-round.
Food
Evening bats generally forage in open habitats such as open woodlands, wetlands, agricultural areas, and along rivers. Flying insects, including mostly beetles, cicadas, and true bugs, are the primary foods.
When foraging during the last half hour of daylight, an evening bat flies 40–75 feet high. But as darkness falls, the bat comes closer to the ground, sometimes spiraling downward from these heights. Usually there is a peak of feeding activity after the bats leave the roost and a lesser peak before reentry in the morning. If young are in the roost, females return midway through the night to feed them.
It has been estimated that a single evening bat can consume about 21,000 insects over the course of a summer.
Status
Native Missouri bat.
Life Cycle
Mating occurs in late summer and probably again in spring, during migration and with males occasionally visiting colonies. The length of the gestation period is unknown, but presumably the eggs are not shed from the ovaries until spring. The young — usually twins — are born around the middle of June. Each weighs about 1.4 g (0.2 oz.) at birth.
The newborn young are nursed by their mother. During their third week of life, they can begin to fly about but continue to nurse, sometimes communally, until 4 weeks of age. In captivity, as the young grow older, the females are not particular about whose young they nurse.
Control
Human Connections
As with other bats, evening bats help humans by devouring countless insects, many of which are pests: insects that damage crops and orchards, lawns and horticulture, and forest trees, and insects that pester humans.
A great example of how they reduce pests is their feasting on cucumber beetles, one of the favorite foods of both evening bats and big brown bats. The cucumber beetle is a pest on a wide variety of crops: cucumbers, melons, and other cucurbits, plus beans and peas. It eats tender young stems, leaves, buds, and flowers. It also chews garden flowers. Its larvae, called corn rootworms, burrow in soil and attack roots of corn, destroying crops. Cucumber beetles also spread bacterial wilt and cucumber mosaic virus.
Because they often live in human-built structures, evening bats are one of the species that people frequently see in the skies over their backyards when the stars are coming out. Some people, recognizing the benefits of having bats nearby to gobble up insects, put up bat houses to help provide additional habitat for these animals. There are many ways to make your yard more welcoming for bats; it’s even called “bat gardening.”
Because most evening bat maternity roosts are established in human structures, this puts these bats at particular risk. As a result of human intolerance and of the removal of aging structures, most of these roosts do not last very long. The degree of impact of these habitat interruptions is unknown.
The first part of the scientific name, Nycticeius, means “belonging to the night.” The second part, humeralis, means “pertaining to the humerus,” which is the bone of the upper arm. The common name denotes the time when these bats are observed to fly about and feed.
Ecosystem Connections
Bats serve an important role in controlling insect populations, but they are preyed upon by many kinds of animals, such as owls and snakes that wait for bats as they exit their roosts in the evening.
Because they roost and raise their young in cavities and loose bark of dead trees, evening bats benefit when landowners allow dead and dying trees (“snags”) to remain standing. Many other cavity-nesting species need hollow places in trees: squirrels, mice, and raccoons, plus many, many birds, including woodpeckers, bluebirds, chickadees, titmice, nuthatches, owls, wrens, chimney swifts, and wood ducks.
The loose bark of dead trees is an important shelter for many types of wildlife, too, and not just for bats. Other animals that rest under loose bark include treefrogs, small snakes, salamanders, and many types of insects, especially as they overwinter as eggs or pupae. Brown creepers — small brown birds that creep around on bark and look like bark — hunt for insects beneath loose bark and also build their nests between the trunk and a piece of peeling bark. Their nests are like little hammocks!
Evening bats are particularly prone to infestations of mites or bat bugs.
