I think we might have some bats living in our attic. We’ve seen them go in and out by the roof line. Do they eat mice? What else could they be feeding on at night? L.L., Boston, MA

The two bats in our region (little brown bat and big brown bat) are predators, feeding almost exclusively on flying insects. Some 70% of bat species eat insects. In tropical regions, fruit and nectar-feeding bats pollinate flowers and disperse seeds to help regenerate rain forests. There are even a few specialized bats that are carnivores on frogs or that suck blood from cattle (fortunately they’re only found in Latin America).

That’s a Lot of Bugs in a Belly

Since bats hunt at night, they are feeding on night-flying insects like mosquitoes, midges, moths, beetles, and leafhoppers. They use their echolocation, a type of sonar, to locate and zero in on flying insects. Some bats can consume up to half of their weight in insects in a single night. A little brown bat can capture 600 mosquitoes in an hour. In the Boston area, it’s estimated that the approximately 50,000 big brown bats that live within the bounds of Route 28 consume 14 to 15 tons of insects each summer!

Many of the insects that bats eat, like moths, are agricultural pests in their larval stage, so the bats perform a valuable pest control service for growers. The fact that they eat tons of annoying mosquitoes endears them to people. This insect-eating lifestyle is one reason why bats are considered to be beneficial animals and why they are protected by federal law.

We Love ‘Em, But We Don’t Want to Live With ‘Em

While bats are beneficial mammals, most people don’t want to live with them in their home. Bats can carry and transmit rabies, and large amounts of their droppings (guano) can attract insects. Droppings and urine can smell and stain ceilings below. Bats in an attic roost are noisy, with lots of squeaking and scratching.

If you have bats living in your attic, now is the time (fall-winter) to block them from getting in and to permanently seal up their entrances (see Early Fall is the Time to Exclude Bats From Your Home). In Massachusetts, we can exclude bats from buildings only during the months when there are not young in the nest. Give Colonial a call and ask us about our bat inspection and exclusion program.

Photo credit: USFWS Headquarters / Foter / CC BY