Prairie State Wildlife

Bats:   Big Brown Bat   Eptesicus fuscus   and   Little Brown Bat   Myotis lucifugus

Most Illinois bats are members of the evening bat family and bats are unique because they are the only true flying mammals.

They are most active during the evening, night and early morning hours.  Bats are inactive during the brighter hours of the day and find refuge in hollow trees, caves, buildings, attics and areas between walls in vacant and non vacant residences.

The little brown bat and the big brown bat are the species most commonly found in buildings and are responsible for most of the service calls to our office. 

The big brown and little brown bats are insectivorous and feed on numerous varieties of flying insects.  These bats feed on species such as mayflies, mosquitoes, moths, caddisflies, flying ants and beetles. 

Bats mate in fall and winter but the female retains the sperm in her uterus until spring when ovulation and fertilization take place.  Female bats usually give birth in May, June and July and often congregate in colonies while raising their young.  Young bats grow quickly and are flying with their parents within a month’s time.  Most bats are weaned by July and August and the nursery colonies then disband.  It is because of this tendency for bats to have a nursery in a residence until late August, that we schedule many of our bat proofing appointments after September 1.  Few bats overwinter in buildings.  As winter approaches and temperatures drop, bats will begin migration to hibernation areas both near and far.  Bats spend the colder months in hibernation waiting for warm weather and a new supply of food.

Customers may become aware bats are present because a single bat may be discovered in the living area of the residence (big brown bats).  Noise can also develop behind a wall, in the eaves, in the attic or a customer may discover bat feces (guano) in the attic, in a wall space, or on the exterior of the residence.

Bats often enter buildings to roost and find refuge.  Bats can enter small openingsBat roosting site. and cracks as narrow as three-eighths of an inch.  They often gain entry into a building via openings in the roof peaks and valleys, fascia boards, ridge caps, the drip edge, flashing, soffit, dormers, around windows and conduits (plumbing, air conditioning).   Often times bats leave rub marks at the point of entry into a structure.  These rub marks appear smooth and have a polished appearance caused by secreted oils, debris and urine deposited as the bats exit the structure.  If large numbers of bats reside in a home, considerable noise may come from the colonies activities.  Bats make noise as they groom themselves, scratch, crawl, climb and shuffle about.  Noise is most often heard as the bats enter and leave the structure.  On very hot days they can often be heard adjusting their location according to the heat building up in the chosen roosting area.

Please note that precautions must be taken while working with bats.  Bats can carry the rabies virus.  Therefore caution must be taken when handling these animals.  Never handle one without a thick leather glove for protection and prevent exposure of the animal to other humans and domestic animals.  Also, when in contact with areas covered in bat guano, please use a respirator as you do not want to expose yourself to Histoplasmosis, a microscopic fungus known to grow in and on bat guano.Bat guano (feces) located below roost site.

Damage prevention involves a thorough inspection of the structure from top to bottom for possible entry into the residence.  Once all possible entry points are identified, seal all points with appropriate materials (roofing cement, caulk, etc.), installation of wire and new flashing if required.

Control methods can vary depending on the severity on the infestation and the size of the bat colony.  A lone bat may be removed by hand with the proper precautions taken.  A large colony would require the sealing of all possible entry points into the structure and the installation of devices (netting, one way check valves, traps) that prevent the bats from reentering the structure or capture of the bats outright.



Prairie State Wildlife
P.O. Box 224 Oswego, IL 60543 US
Phone: (630) 687-3414 Website: