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Big Brown Bats


Family:  Vespertilionidae – often shortened to Vesper

Genus:  Eptesicus – Greek for house flyer

Species:  Fucus

Weight:  14-23 grams or .5-.8 ounces

Wingspan:  13-16 inches

Lifespan:  average is 10 years, but live up to 19 years

Predators:  cats, falcons, humans, owls, raccoons, and snakes

Unnatural causes of death:  DDT and other pesticides

The big brown bat inhabits the lower 48 of the United States, southern Canada, and Mexico.  Some colonies remain year-round.  Others may travel 150 miles to hibernate further south.  The big brown bat is a wonderful pesticide provided by nature.  Consequently, there is no need for artificial insecticides that contain poison.  Plus the guano is a fabulous addition to compost.  In fact, some gardeners have told me at flower and garden shows that they hang their bat houses directly over gardens.

This species mate in the fall or winter, but store the sperm until April.  The males generally live separate from the females and the pups.  For example, the big brown bat colony would prefer a minimum of a bachelor pad and a nursery house.   Big brown bats on the east coast often have twins.  The big brown bats on the west coast usually have single births.  Births are between late May and early June.  The pups begin flying during the third week.  By nine weeks the pups are flying and eating with the adults.

The pups are left at the bat house while the females feed.  Consequently, a pup may fall.  The pup should be left where it is.  It will squeak until its mother returns.  She will pick the pup up and return it to the bat house.

The big brown bat generally eats many varieties of beetles.  It is also known to eat flying ants, several species of flies, mosquitoes, wasps and other insects.  Big brown bats normally fly between 20 feet and 30 feet.  Big brown bats hunt using echolocation and catch the insects in flight using their wings.  Because of following the path of an insect intent on escaping capture, these bats often appear to be flying erratically.  The big brown bat is an efficient feeder.  Most eat their fill within an hour.  Females may eat their body weight in a feeding.  According to the experts a bat is one of America’s most beneficial animal.

If you are interested in watching insectivore bats, including the big brown bat, feed, there are some locations that will be better than others.  Sit around a street light or near a water source after sunset.  The big brown bat usually begins feeding a half hour after sunset.  Some of our customers have seen bats feeding around their patio lights and enjoy watching the bats as they chase their prey in an erratic flight pattern.





White-nosed syndrome is a fungus.  The scientific name is Geomyces destructans.  It appears to thrive in cold, humid areas or where bat colonies prefer to hibernate.

Big brown bats are threatened by white-nose syndrome.  Many have succumbed to this fungus in eastern United States.  Bats are infected while hibernating in caves.  The mortality rate is around 90%.  For the most up-to-date information, visit http://www.batcon.org/.  White-nosed syndrome began in ONE New York Cave in 2007.  It is now as far east as Indiana and south to Maryland.






Ohio Division of Wildlife Publication 372: Life History Notes Big Brown Bat


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