The bats of Will County

Get to know the eight species that call the preserves home

| Story by Meghan McMahon |


Bats are one of the most prolific animals in the world, with more than 1,300 species living on six continents. 

In all, Illinois boasts 12 species of bats, with eight known to live within the forest preserves of Will County.

These flying mammals play an essential role in the environment, consuming huge amounts of insects every night, including pesky mosquitoes and agricultural pests that can damage crops. In more far-flung locales, bats also pollinate plants.

Today, bats are threatened by both habitat destruction and disease. In the United States, white-nose syndrome, a fungal illness, has killed more than 5 million bats.


Bats that can be found in the preserves include:

Big Brown Bat

A big brown bat.

Photo by Glenn P. Knoblock

As the name implies, big brown bats are big, but only by bat standards. These creatures typically weigh in at no more than three-quarters of an ounce, with bodies between about 4.5 inches to 5 inches long. In addition, their wingspans range from about 13 inches to 16 inches.

Big brown bats do not have fur on their ears, wings, faces or tails. However, their bodies are covered with fur, and it can range in color from light to dark brown, or sometimes even reddish-brown.

This species’ presence in Illinois is hardly unique. The big brown bat lives across the United States in almost every kind of habitat, including deserts and forests. They roost in hollowed-out tree trunks and caves, but also in man-made structures. In fact, big brown bats are one of the bat species most commonly found in homes and other buildings in Illinois.


Eastern Red Bat

An eastern red bat in a tree.

It won’t come as any surprise that eastern red bats are red in color, but the shade can vary greatly, from brick red to brownish-red to an orange- or yellow-red. The ends of its fur are white in color, which makes them look frosty.

Eastern red bats have long fur that helps protect them from cold temperatures, and they also have a tail membrane that they can wrap around themselves like a blanket. Their bodies are smaller than some of the other bats we see locally, typically between 3.5 inches and 4.5 inches, and they weigh less than half an ounce.

These are solitary bats, living alone except to mate and during migration, and they are tree dwellers, roosting in the foliage of both deciduous and evergreen trees. Their reddish color can help them blend in, looking like brown leaves or pine cones, Bat Conservation International reports.


Hoary Bat

Close-up of a hoary bat.

Photo by Daniel Neal [CC BY 2.0  (], via Wikimedia Commons.

Hoary bats are the most widespread of the all the bat species found in the U.S., and they are the only bats found in Hawaii, the University of Michigan reports. They typically are found in and around tree-covered areas, and they live in both urban and suburban areas. Hoary bats are mostly solitary and are rarely found in man-made structures.

These bats get their name from their coloring, with their scientific name, Lasiurus cinereus, meaning “frosty or ash-colored hairy tail.” They have long, thick hair on their backs as well as under their wings and arms, and the fur is usually a grayish-brown with a white tinge, giving the appearance of being frost-covered. Hoary bats have small, round noses and beady little eyes.

Their bodies are typically between 5 inches and 6 inches long, and they look like that of a mouse. Their wingspans range between about 16 inches and 17 inches, and they weigh between three-quarter of an ounce and 1.25 ounces.

Silver-haired Bat

A silver-haired bat.

Photo by Larisa Bishop-Boros [CC BY-SA 3.0  (], from Wikimedia Commons.

Silver-haired bats don’t have silver fur; instead, their brown or black fur is lighter at the ends, usually white or yellow, which gives the appearance that they are silver. They are similar in appearance to both the hoary bat and the big brown bat and are often confused with both, although they are smaller than those species.

Silver-haired bats’ bodies are less than 4.5 inches, with wingspans between 10 inches and 12 inches. They are lighter than big brown and hoary bats too, weighing less than four-tenths of an ounce. Other features that set them apart from similar-looking species are their upturned noses.

These bats are also tree dwellers, but typically live only in old growth forest areas. They usually form colonies in holes in trees, and will often move from roost to roost.

Little Brown Bat

A little brown bat.

Photo via Shutterstock

Little brown bats are small compared to the similarly named big brown bats, weighing in at less than half an ounce. Their bodies range from 2.5 inches to 4 inches, and they have smaller wings than the big browns too, generally between 8 inches and 10 inches long. They have shiny fur in various shades of brown, including dark, olive, reddish and golden brown. Their wings and legs are also brown, but with little to no fur.

Along with big brown bats, little brown bats are one of the most commonly found bats in homes and buildings in Illinois, the Illinois Department of Public Health reports. Colonies of hundreds or even thousands of bats have been found living inside man-made structures. They also roost in trees or under rocks and piles of wood. Little brown bats are unusual among the bat species we see in Illinois in that they maintain separate roosting spots for day and night.

Northern Long-eared Bat

A long-eared bat.

Photo by U.S. Fish and Wildlife Service, Al Hicks.

As you might guess from its name, the northern long-eared bat is distinguishable from other bats we see in northern Illinois by its long, rounded ears. They have yellowish-brown fur, and their undersides are gray. They are a medium-sized bat, weighing less than one-third of an ounce with bodies that are about 3 inches and wingspans range between 9 inches and 10 inches.

These bats live in dense forests, roosting in holes and cavities of trees or under the bark. Northern long-eared bats are solitary, typically living alone or in very small groups.

Evening Bat

An evening bat.

Photo by Enwebb [CC BY-SA 4.0  (], from Wikimedia Commons.

Evening bats come out soon after dusk to hunt for insects, hence their name. They are a medium-sized bat, weighing less than half an ounce with bodies ranging from 3 inches to 4 inches and wingspans of between 10 inches and 11 inches. They are dark brown with black ears, and like many bats they have no fur on their wings, tail membranes and noses.

These bats are never found in caves, instead preferring to live in forests and along rivers and in wetlands. They often nest in tree hollows or under the bark of trees, but they are also sometimes found living in man-made structures.

Tri-colored Bat

A tri-colored bat.

Photo via Shutterstock

Like evening bats, tri-colored bats are among the first to emerge after dusk. Their name comes from the fact that each of the hairs on these bats is three colors: dark at both the base and tip and a lighter, yellowish-brown in the middle. They are smaller than many of the bats in the preserves, typically weighing no more than a quarter ounce with bodies ranging from 3 inches to 3.5 inches and wingspans of less than 10 inches.

Tri-colored bats, which used to be called eastern pipistrelles, are more sensitive to cold weather and, as a result, hibernate earlier than many other bat species and emerge later than most. During the warmer months, they are often found near water. They roost in forest foliage, caves and crevices, as well as in buildings.


Lead image via Shutterstock

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