Bats are the world’s only flying mammal.  Both of the two most common bat species in southwestern Ontario, the Big Brown Bat and the Red Bat, will regularly use bat houses.

Big Brown Bat (Eptesicus fuscus)

• length: 11.5 cm (4.5 inches)

• weight: 19 grams (0.6 oz.) or about as much as 2 loonies

• wingspan: 33-39 cm (13-16 inches)

• the most common bat species locally in urban and rural areas

• regularly uses bat boxes

• species that is most likely to hibernate in Ontario, although many big brown bats will migrate

• may hibernate in buildings where the temperature remains above freezing

• hibernates in groups of up to 10,000 bats

Red Bat (Lasiurus borealis)

• length: 10 cm (4 inches)

• weight: 13 grams

• wingspan: 28-33 cm (11-13 inches)

• common in woodlands

• migrates south for the winter

Mosquito Control

All of the bat species found in Canada are insect eaters, consuming vast numbers of insects that fly at night.  A nursing mother bat will often eat up to her body weight in insects nightly, with others consuming between 30-50% of their body weight.  Bats eat an assortment of pest species, including cucumber beetles, cutworm, corn earworm, leafhoppers, June beetles and mosquitoes.

Some bat species can eat from 500 to 1,000 mosquitoes in a single hour, so a large colony can consume enormous quantities.  Keep in mind, though, that a bat will prefer to eat one large insect, such as a June bug, rather than many smaller insects, such as mosquitoes. 

However, mosquito control is a complex problem that rarely can be solved by a single approach, be it bat houses or pesticides. While it is impossible in most cases to completely eliminate mosquitoes either by chemical or natural means, their numbers can be substantially reduced. In the long run, this is best done by non-chemical means, such as by draining unnatural sources of standing water and encouraging predators such as bats, fish and aquatic insects.

Existing chemical pesticides typically cause more long-term problems than they solve. Chemical poisons kill natural mosquito predators more effectively than they kill mosquitoes. Some of the main mosquito predators include dragonflies, spiders, frogs, salamanders, purple martins, bats and fish. Over time, pesticide build-up can cause predators such as fish, dragonflies and bats to die out, while mosquitoes develop resistance that enables them to multiply in ever-larger numbers.

Despite the numbers of mosquitoes that bats eat, simply providing additional bat houses or roosts is just one step towards solving a mosquito problem. Bat houses may not result in more bats, because most urban habitats are not overly diverse and cannot support more than a few bats. Even rural areas are relatively simple farms that may produce huge hatches of mosquitoes and other insect pests on an occasional basis, but not a continuous supply. Storm water management facilities may allow for a more biologically diverse ecosystem that may be able to better support bat communities.

Bat houses are most likely to succeed where bats are already known to use old buildings, barns or bridges. However, such roosting habitat is often replaced by structures that are unsuitable for bats, forcing them to find new roosts or die. Of equal concern can be the loss of hibernation caves hundreds of miles away which may preclude further use of an area by a bat species that feeds on mosquitoes.

Although additional roosts alone may not attract bats, in this area if we put up bat houses and they do attract bats, they will likely feed on mosquitoes. While mosquitoes may bother us most directly, many beetles, moths and other insects consumed by bats are major yard and garden pests , such as cucumber beetles, cutworms, corn earworms, leafhoppers and June beetles. Building bat houses can help in many ways, though not always in mosquito control.

Threats to Bats

• disturbance - when roosting or during hibernation

• pollution - bats need clean water

• pesticides - when a bat eats an insect, it is also eating any chemicals that insect has eaten or absorbed

• deforestation - bats need trees for roosting and hunting for food

How We Can Help Bats

• avoid the use of pesticides

• plant trees

• protect tree snags

• plant a garden that attracts insects that feed bats

• put up a bat box

• do not enter a cave if bats might be roosting or hibernating in it

It’s a Myth!

• Bats are not blind. They navigate by "echolocation", which is the use of high frequency sounds to navigate and communicate. Like submarines/sonar radar, they send out pulses of sound and the returning echoes enable them to detect obstacles in their path.

• Putting up a bat box in your yard will not attract bats to your attic. If your attic would make good bat housing, they're already there.

• Bats are not attracted to your hair, although bats can detect a human hair from 1 metre away.

• In the eastern United States, there have been cases of West Nile virus documented in other mammals, including cats, domestic rabbits, chipmunks, gray squirrels, striped skunks, bats and horses. There have been no documented cases of West Nile Virus being passed from one animal to another, or of an animal infecting a human. Symptoms in animals can include any combination of the following: fever, weakness, lack of coordination, muscle spasms, seizures, and changes in temperament or personality.

• In Ontario, 67% of wildlife rabies cases involve foxes, 30% involve skunks, and less than 3% involve bats, coyotes, and other wildlife.

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