Some bats do eat mice.

More Info: Though some carnivorous bat species do eat mice, carnivorous bats comprise less than one percent of bat species. Sixty to seventy percent of bat species are insectivores feeding on a variety of insects that fly at night such as moths, gnats, flies, crickets, and even wasps. 

What Do Carnivorous Bats Eat?

There are a wide variety of carnivorous bats that eat a variety of prey, which includes mice, birds, frogs, fish, and even other bats to name of few.  The false vampire bat, for example, will eat rodents, insects, and spiders.  The frog eating bat eats...you guessed it....frogs.  These bats can eat up to 40 frogs in a single day.  The vampire bat is the only mammal that feeds solely on blood.  Its primary prey are cows and horse but these bats have been known to feed on humans.  The bat's bite is not deadly, but it can carry infection and disease.   

The Essential Insectivorous Bat

Mosquitoes are a favorite food of the insectivorous bat, which is why homeowners will attempt to encourage bats to roost around their property by placing bat houses.  Bat colonies are able to literally devour tons of insect weekly.  In fact, one lone tiny brown bat can eat 1,200 insects in one hour.  Now there's the perfect mosquito repellent!