Go Batty For Beneficial Little Brown Bats

October is bat season! We love bats for Halloween decorations, and we tell spooky stories about them around the campfire. Plus, this is a great time of year to watch them flying around at night, catching food to fatten up for winter. Let’s swoop in to learn about one of the most common Illinois bats: the little brown bat.

A little brown bat. (Photo via Shutterstock)

Someone ran out of creativity when they named the little brown bat. These bats are little and brown! In fact, at their smallest size, they weigh only 5 grams, which is only about as much as a nickel. The largest little brown bats will weigh about 14 grams, which is about as much as three nickels. For their tiny size, they have a huge wingspan of 9 inches to 11 inches.


They may look like mice with wings, but they live a lot longer than mice. In the wild, their average life span is six to seven years, but they can live much longer. In captivity, bats can live 20 to 30 years. The oldest recorded little brown bat lived to be 34 years old.


Here are some cool facts about little brown bats.

  • They are the only flying mammal. Well, them and all other bats. Do they have hair? Check! Are they warm-blooded? Check! Do moms feed milk to their young pups? Check! Are pups born alive? Check! These are traits all mammals have.

  • Moms can ID their pups through sound and smell! When a bat flies back to the roost at night it must be able to pick out its pup from all the other pups. Mother and pup even have their own way of communicating.

  • They are nocturnal. Little brown bats are most active two to three hours after dusk and in the early morning hours.

  • They have a massive appetite. Little brown bats love to eat insects — lots and lots of insects. An adult male can eat half its body weight in insects every night! A nursing female is even hungrier, gorging on her entire body weight of insects each day. That would be like a 60-pound third-grader eating 30 pounds to 60 pounds worth of burgers and pizzas and French fries all in one day. Oh, my!

  • The best time to see them eat is about two hours after sunset. Look for little brown bats foraging by swooping in wooded areas, fields and over water. They even eat insects that live in the water. Midges, beetles, caddisflies, moths, mayflies, lacewings and mosquitoes are all on the menu.

  • They can “see” in the dark with their mouths and ears! Like other bats, little brown bats use echolocation to hunt. They blast out calls and listen for the echo. Based on the echo, they know where a mosquito is flying. Echolocation lets them find insects to eat and stops them from crashing into other objects at night. In fact, scientists found when bats rely on sight over echolocation to forage, they often crash.

  • They have three homes and a bonus place, called roosts. Real estate is important to little brown bats. They have one roost for the day, one roost for the night and another one for hibernation in the winter. Plus mothers and their pups have a fourth roost that serves as the nursery!

  • Day and night roosts are used by active bats in spring, summer and fall. These roosts are found inside buildings, in trees, under rocks and in piles of wood. The most important thing for day roosts is to keep out the light. Night roosts are mostly used when the temperatures dip below 60 degrees Fahrenheit.

  • They hang out together. A single bat roost can house as many as 300,000 bats!

  • They spread out their poop. By keeping day and night roosts at the same time, little brown bats don’t have a buildup of feces. This is great for keeping a clean house — and to keep predators off their scent.

  • Grooming is very important to them. Little brown bats use their claws to groom their fur and their tongues and teeth to clean their wings. They spend a lot of time doing this.

  • They migrate up to 200 miles to find a cave or abandoned mine for their hibernation roost. They chose places where the temperature will stay several degrees above freezing, with little air flow and lots of humidity. They hang by themselves or with a couple other bats.

  • Their body temperature drops to about 40 degrees Fahrenheit during hibernation. This slows all their other body functions. The heart rate of a little brown bat in flight is over 1,000 beats per minute, but their heart rate in hibernation is only about 5 beats per minute!

  • They hibernate from November until March or April. Little brown bats bulk up on insects beginning in late summer throughout the fall. This gives them the fat reserves they need to survive while hibernating in the winter. They will occasionally wake up to drink, urinate or change locations.

We love bats because they are so interesting! Plus, they play an important role in our ecosystem and our lives. They are food for other animals like owls, falcons, hawks, foxes and raccoons. They eat so, so many insects that they help farmers control agricultural pests that could damage crops and keep disease-carrying insects like mosquitos in check. They are even indicators of environmental health because they are sensitive to habitat fragmentation and landscape changes.

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