Monday, 9 February 2015

The Bats are Back: Tips for keeping them out of your house.

The following article was published in Rural Delivery ( in 2006. 
After de-batting houses for 15 years or so I thought that it was time to pass on some of what I'd learned. 
I'm re-printing the article with permission from RD.
Some new photos have been added to better illustrate what's written. 
I hope you find this of use!
THE BATS ARE BACK:  Tips for keeping them out of your house.
Love 'em or hate 'em, the bats are back.  Many go unnoticed as they roost in backyard trees or comfy crevices.  Others make memorable impressions when they appear in living rooms.  Some cause problems as they fill attics with guano and night noises.  Rural and urban dwellers alike may encounter any number of bats over the course of a year and, along with snakes and spiders, they remain one of the least-liked of our wildlife.
This tiny creature is the Western Small-footed bat.  It weighs only
four grams - the weight of two dimes!  It is a blonde bat with a
black mask.
Bats begin to wing their way back to their summer flapping-grounds in early spring.  Some have spent the winter hibernating in nearby caves, mines and houses.  Others have migrated northward - like summer tourists - from warmer climates where they have been active all winter.  Most return to the same haunts year-after-year.  They set up territories around streetlights and skillfully prevent competitors from eating the insects that swarm there.  Others return to attics where they may have summered for 30 years.  Each species has a unique natural history and a different set of behaviours.  There is no such thing as a 'typical' bat.
Northern Red Bat (Lasiurus borealis). 
Tree-roosting species like the Red bat are
unlikely to show up in your house.
Until you've met some of the 20 different species found in Canada (nearly 1000 worldwide), it is tough to appreciate their differences.  Although all our bats are insectivorous, they range in size from the tiny Western small-footed bat - a four gram (the weight of 2 dimes) blonde bat with a black mask - to our largest, the 28 g, multi-coloured Hoary bat.  For reference, a dime weighs two grams, a quarter five grams, and a chipmunk around 60 grams.  Hoary bats have the largest wingspan - 40 cm (16 inches) of all Canadian bats.  A bats size is tough to estimate on the wing, and is often exaggerated.  Shadowy distortion and tricks of the brain, perhaps.  Intermediate-sized bats included Silver-haired, Red, Long-legged, Long-Eared (Northern, Eastern & Keen's), Fringed, Pipistrelle, Yuma and Spotted bats, among others.  This list includes world record holders - like the largest litter (Red bat), biggest ears (Spotted bat) and, quite possibly the longest-lived (Little Brown bat), thought the latter record is not easy to know. 

This Hoary bat (Lasiurus cinereus) is our largest, weighing 28 grams.
It is multi-coloured and has the largest wingspan of all Canadian
bats - 16 inches)
If you've shared your living space with bats, they are either Little brown bats (Myotis lucifugus) or Big Brown bats (Eptesicus fuscus).  In the Atlantic provinces it is usually the former.  Weighing in at just seven grams (equal to a loonie) these bats frequent buildings.  Males and females of this species behave quite differently, spending much of the summer apart before they meet in autumn to mate and hibernate.  Females store sperm for the winter and emerge pregnant.  They seek hot places, like attics, where they can stay warm throughout the day.  The warmth accelerates gestation and affords the time needed to give birth, nourish pups and bulk up for winter - a crucial adaptations where summers are short.  Human habitations have likely helped some species extend their ranges as far north as the Yukon and Northwest Territories and to Alaska.
Male Little Brown bats have a different plan.  They stay active at night but seek cool places - under siding, in wood piles, between bricks or under tree bark during the day.  Lower temperatures allow them to drop their body temperature, enter torpor (a short-term hibernation), conserve energy and fatten up for winter.  Females adopt a similar routine once the task of giving birth, rearing and weaning the pups is done.
A baby Little Brown bat (Myotis lucifugus).  In the Atlantic Provinces
 it is the breed that is most commonly found living in houses.
Born at about a quarter of the mother's weight (ouch!) a bat pup grows quickly on the milk it suckles from its mother.  As the put gets heavier, mom starts to leave it behind while she forages.  This is when the maternity colony may become conspicuous to the humans living below.  Hungry pups are noisy while waiting for mom, and even more boisterous when she returns.  After about four weeks, the young bats can fly and the colony may evacuate.  When the pup can feed itself - about mid-June to early July - mom's job is done.  Now both must conserve energy by abandoning the warm day-roost and seeking cool places.
A Little Brown bat flying inside and attic.  This bat weighs just
seven grams - equal to that of a loonie.
Young bats may be slower to adapt and occasionally get caught inside the house before they figure things out.  Unfortunately, frantic homeowners sometimes take after them with tennis racquets & brooms.  The bats won't intrude again if you either wait for them to land (often high on a curtain rod) and escort them bout in a tea towel, or direct them towards and open door by blocking their flight path with a towel.  Opening several doors or windows to create a cross-breeze will also show them the way out.
As autumn approaches, bats gradually make their way back to hibernacula to begin the cycle again.  Mortality is especially high in young bats (called young-of-the-year or YOY).  The proximity to humans, coupled with seasonal dangers, especially early or long winters, means that about half of the young bats don't survive their first year.  Disturbances during hibernation can also be disastrous.  Agitated bats waste precious body fat and may not survive until insects reappear.
Bats do, however, wake up throughout the winter.  As temperatures fluctuate, they may need to migrate inside the cave to find the ideal temperature and humidity.  It is not uncommon to see Big brown bats, which will hibernate in houses, awaken and fly about the yard or living room in mid-winter.  Christmas can also be a busy time.  Seems turning the thermometer up for grandma's visit and poking gifts into secret places isn't conducive to hibernation.  Others, low on fuel and desperate for grub, emerge in March and April - too early to be able to find food - and die from starvation.
 So, what can you do if bats have claimed your attic and you'd like to evict them?  First, don't resort to poisons, noxious sprays and home remedies like bright lights, loud noises, ultrasonic rodent repellers and mothballs.  None of these 'remedies' work.
 Bats, except non-volant young, leave your house every evening to feed and you can then bat-proof to keep them out.  Imagine your house as if it was a cardboard box.  If the perimeter of that box is closed, nothing will get in - except through doors and windows (check screens!).  If these openings are secure and the bats still get in, there are other entrances to attend to.  Little brown bats can squeeze through a gap the width of an index finger.  The most likely points of entry are where the roof meets the walls of your house (check all eaves, soffits, facia and gables for gaps) and around chimneys (check the metal flashing). 
Typical ways bats get in!
A day spent inspecting and sealing the edges of your hose is in order.   Do this before the bats give birth or after they move out - otherwise you risk locking the pups inside.  Use the bats to tell you how they get in.  Ask some volunteers to help watch your roofline at dusk on a clear night.  Noises in the eaves and swooping bats will reveal the main exits.  Guano stuck to a window or wall is also a telltale sign - bats often urinate and/or defecate before they land so the entrance is just above the mess.
After sealing up all but the final entrance or two, you can install a one-way chute and let the bats clear out on their own.  Snip off the end of a bread bag, affix it to the house (with staples, tape or caulking) and wait for the bats to flop out and fly away.  I use heavy plastic (vapour barrier) and fashion it into a tube that tapers away from the house.  Bats that want back in usually nose around the base of the tube and finally leave at dawn.
Looking up into a one-way chute fashioned from heavy
gauge plastic
A colony of 500 or more bats can be convinced to leave in just a single night or two - and you never have to see or touch even one.  The new exit can force some bats to stay in for a night or two and may bring several downstairs.  Be patient with the first group (wait about three nights) and escort the second group out as described above.

Big Brown bat attempting to get back into the house
after evicting itself.
Once you're convinced the bats are out, remove any remaining chutes, seal the openings and proceed with clean-up.  Bat droppings are not poisonous, as many people suspect.  They actually consist of chewed up insects.  As droppings accumulate, fungi and start to grow and their spores can cause problems.  Histoplasmosis - a respiratory ailment - is a nasty one. Guano can be vacuumed up (wear a tight-fitting mask) and used as a nitrogen-rich fertilizer  The smell from urine-soaked insulation may warrant removal and the use of a fogging -device (to spray a scented mist) will mask some of the musty odour. 
Problem solved!  If you feel pangs of guilt after the eviction, consider providing alternate accommodation for bats by erecting some bat houses.  Bats won't leave the attic to move into a bat house, but they may find solace there after the attic closes for good.  But that is a different story. 
(Matt Saunders has a B.Sc. and a B.Ed. from Mt. Allison University & a M.Sc. (in bat behaviour) from the University of Calgary.  He grew up near Truro, N.S., and starte a small business called Bat Check in 1990 to both educate people about bats and help them deal with bat problems.  he has evicted bats from many houses in the Maritimes and Ontario.  He currently resides in Seeley's Bay, ON with his wife Heather (a veterinarian) and a menagerie of dogs, cats, chickens, goats, sheep and a Newfoundland Pony.  Together they rehabilitate injured and under-nourished bats throughout the year.  Matt is currently the Head of Science at Kingston Collegiate and Vocational Institute where he has taught science, biology and environmental science for the past 15 years.)


  1. The bat that you called me about came out of the ducts at night, and with some tips from your site, i helped direct it to an open door.

    Thx for the tips on the site, it was very helpful. I will share it with my family so they can get any remaining bats out (with the one way chute) and then seal up the opening they are using to get in.

    Rock on bat man ;)