Bats – Beneficial or a Nuisance?

Recently on the news, it was announced that bats carry rabies.  This is true to a very small extent.  After listening to their news report the average person would come away with the thought that most bats are dangerous and they all carry rabies.  The reality is that a VERY SMALL PERCENTAGE carry rabies.  The droppings they leave behind may harbor the fungal organism that causes the lung disease histoplasmosis.

Bats are very beneficial since they feed on insects such as;  beetles, wasps, ants, planthoppers, leafhoppers, flies moths… because of what they eat makes them a very useful animal.  They have been known to consume about 200 mosquitoes an hour.  Bats are nocturnal, they leave their nests at dusk and return before dawn.  Their first stop is to water and then they begin their feeding.  

Bats roosts are located in attics and behind shutters and loose boards on buildings.  If bats are roosted in your attic or outside on your home, your goal should be to only relocate them, not kill them.  Bat houses can be bought or easily built and mounted on a nearby tree or a post.  They will then relocate into the bat house.  You still keep your bug killer, yet eliminate a roommate.  After they have transferred to the bat house or after they have left for hibernation in the fall before spring; it is important to bat-proof your home, closing up any entries they had.  Be sure to wait until after mid-August if you are doing this in the summertime.  Exclusion is the only method to keep bats out long term.

Ultrasonic devices have not been found to be effective for repelling bats from structures and using bright lights can only help, but total control should not be expected.

Steps to Total Control

     1. Determine points of entry. 

               The locations to pay close attention to are; attic louvers, roof lines where sheeting and facia boards meet, under facia boards and other openings due to deterioration.  The best time to inspect is from ½ hour before dusk until one hour after dusk.  Keep in mind that bats will not fly in rainy or unseasonably cold weather.

     2. Inspection during the day is done to find any exterior structural deficiencies and inside roosting sites. 

               Look for droppings or bats access problems.  You should be wearing protective equipment when entering a bat roost due to the droppings dust which can be inhaled.

  • respirator with HEPA filters 
  • coveralls
  • heavy leather gloves
  • bright flashlight
  • bump cap  

               Seal all but 1 or 2 entry points and all other holes 3/8 inch or larger.  Then wait 3 to 4 days for the bats to adjust.  After that then seal those remaining holes in the evening just after the bats leave for their night feeding.  If you have the problem of too many holes, then the installation of plastic bird netting is your answer, which can be cut to a size which will cover the opening.

     3. After the bats have been excluded and all entrances have been barred, the roost area should be treated to help control the bat ectoparasites, such as mites and bat bugs. 

               Many of these will bite humans.  ULV and/or apply an appropriately labeled residual to the area.  These areas either need to be inaccessible OR they can be professionally decontaminated and removed.

               Bats have relatively poor vision so they rely on echolocation to avoid objects and find prey.  This is very similar to sonar.  They emit about 30-60 squeaks per sec with a pitch of 30-100,000 cycles.  The squeaks are projected through their nose or mouth and the sound wavelengths reflect off of objects and return to their ears.  


Big Brown Bat

Size:  4 1/8 to 5 inches
Wing Span:  12-14 inches
Weight:  2/5 to 3/5 ounce
Teeth:  32
Life Span:  max 19 years
Flight Speed:  up to 40 mph, fastest reported for any bat
Hibernate:  December to April

Little Brown Bat

Size:  3 1/3 to 3 5/8 inches
Wing Span:  8 11/16 to10 5/8
Weight:  1/8 to ½ ounce
Teeth:  38
Life Span:  max 20 years
Flight Speed:  average 12.4 mph, up to 21.7 mph
Migration:  south in the fall
Hibernate:  September/October through March/April

Bat Information