Bat Big Brown

Binomial Name: EptesicusFuscus


  • Forearm: 4.4-5.1cm
  • Wingspan: 32.5-35cm
  • Ears: 1.6-2cm
  • Colour: Reddish brown to dark brown

Life Cycle: Southern Ontario litter size is two. Big brown bats may live as long as 18 years but in the wild life expectancy is drastically reduced to a few years.

Behaviour: Summer maternity colonies may include approximately a dozen to a few hundred bats while males typically roost in small groups or alone. Big brown bats are sensitive to high temperatures and will choose cooler summer roost sites such as: behind chimneys; in hallow walls; behind shutters and in enclosed eaves. During the winter big brown bats canoverwinter in attics, wall voids and basements.

Signs of Infestation: If you suspect that you may have big brown bats roosting within your home you can verify your suspicions with a “bat watch” – please see the section titled “Little Brown Bats” for more information on how to perform a bat watch. Other signs of an infestation include: physically seeing a bat inside your living quarters, rub marks and guano.
If you see a bat within your living quarters it may be a big brown bat. Big brown bats tend to move about during temperature swings, this can mistakenly draw them into your living space as they seek to exit their roost site to the outside.
Rub marks around small gaps and crevices often indicate the presence of bats. The rub marks are an oily residue which is excreted from bats and builds up as they regularly move over an area. The rub marks will appear smooth and polished and are a sure way to identify a bat entry / exit point into a building.
Guano (bat droppings) will often be present in and around structures where bats are roosting. At a glance, guano looks like mouse droppings. However, and unlike mouse droppings, when crushed guano becomes powdery and reveals shiny bits of undigested insects.