Bat Infestation in the Wine Country

  Bats are nocturnal mammals found in most inhabited places throughout the world.  They are neither rodents nor birds, and they are not blind.  Bat infestation in homes, especially in attics, can be a health hazard, as well as a nuisance, for homeowners. 

I recently had occasion to be up-close-and-personal to this dilemma.  Through my church affiliation, I happen to know a very nice lady whose home is in excellent condition and always very clean.  Yet, she had an infestation of bats.  She hired a company who apparently is not knowledgeable on topic and for a couple of thousand dollars, they removed one side of her house.  That’s right.  They took the exterior wall completely off—“to let the bats fly out.”  They flew out and then they flew back in.  Back to Square One.

In another case of bat infestation, a client of mine who resides on the east coast purchased a fixer upper for his impending retirement in Glenhaven.  After escrow closed, the house received a certain amount of remodeling and repair.  He visited and enjoyed the house for a couple of weeks and then returned home leaving the house vacant.  He asked me check on it from time to time which I did but I was noticing increasing signs of guano and when I had workers come to do the weed eating, the noise drove the bats crazy and they flew out by the hundreds and maybe the thousands.  It was Alfred Hitchcock’s movie all over again.

Well, first we had to locate where they were going in so when they were hopefully removed we could block their access.  I may not be the brightest bulb in the chandelier but I already knew that tearing off the side of the house was not going to work.  I found “the Woodpecker” in Lucerne.  He builds all sorts of things and among them he builds bat houses.  Fast forward to today -- all the accesses have been sealed, all the guano cleaned up, and the bat houses have been installed in nearby trees.  So the bats have relocated themselves to comfortable apartments.


  • Due to its high levels of phosphorous and nitrogen, guano (bat feces) is an effective fertilizer and gunpowder ingredient. Despite how large they appear in flight, bats are remarkably small. Some can fit through openings smaller than ½-inch wide. Even the largest bat – the golden-crowned flying-fox -- with a wingspan of up to 5 feet, may weigh as little as 3 pounds.
  • Roughly 20% of all known mammal species are species of bats.
  • Bats are the only mammals capable of sustained flight.
  • The accumulation of guano. Bat guano resembles rodent droppings but can be distinguished in several ways:  guano tends to cluster as it piles up beneath the exit of the bats’ roost; guano often has a shiny, speckled appearance due to the ingestion of insect wings; and guano can be easily crushed into smaller fragments, while rodent droppings will not. Of course, it is not safe to touch any animal droppings with unprotected hands;
  • Milky white urine stains on windows;
  • Stains around entry holes, such as cracks and crevices;
  • Mouse-like droppings under eaves and overhangs;
  • stains and odors caused by urine and guano;
  • Noises such as squeaking, scratching and crawling in attics and walls shortly before dusk and dawn; and
  • Grease and dirt. Bats often leave smears of grease and dirt from their coats on the entry point to their roost.


This respiratory disease, caused by the fungus Histoplasma capsulatum, is transmitted through the inhalation of fungal spores found in bat guano and bird droppings. Although generally not fatal, histoplasmosis can cause flu-like symptoms. For individuals with compromised immune systems, such as those with AIDS, histoplasmosis can be fatal.


  • The entry point for the bats should be identified. Holes as small a human thumb are large enough for some bats to squeeze through. The homeowner can seal off most of these holes with caulk, leaving one hole intact for resident bats to exit at night.
  • The homeowner can then plug this hole at night so that bats cannot return to the house. Alternatively, the homeowner can install a one-way “check-valve” from wire mesh that will allow bats to exit the house but not allow them to return.    
  • “Bat houses,” which can be constructed or purchased, can be placed next to the house during bat removal to provide bats with an attractive alternative to the house.  

Note:  Bat removal should not take place during the summer.  Baby bats that are unable to fly will not be able to leave the house during the summer months and they will starve to death if adults are not permitted to enter the home. Bat removal during the summer is inhumane and will result in the additional problems posed by decomposing bat carcasses.  

In summary, bats can transmit dangerous diseases to humans, and inspectors and homeowners should be wary of bat infestations.