Bat Control
Last Update/Review: June 17, 2002
Perhaps the most important question in controlling or removing bats is whether or not to do it. Bats are a natural element in the ecosystem and play an important role as predators of a variety of flying insects. All species of bats are considered wildlife and are protected under the Wildlife Act. In particular, it is illegal to disturb bat hibernacula between September 1 and April 30. Bats hibernate for six to seven months of the year and are inactive for up to 20 hours each day during the summer. They are inconspicuous and unobtrusive. The prevalence of diseases in bats in Alberta is so low that widespread eradication of bats to eliminate a human health hazard is unjustified.
Contrary to folklore, bats are not elements of evil. Although a few cases were reported in the early 1970s, bats do not indiscriminately attack people nor are they particularly attracted to ladies hair. However, bats are not always blameless. As indicated earlier, some bats have the annoying habit of roosting in or on occupied dwellings. This is not always appreciated by the people sharing the building. Bats produce large amounts of urine and faeces which may result in odor and damage to wooden surfaces. Note that they do not chew insulation, electrical wires, or structural elements. Thus, damage usually is minimal and the problem is psychological more than anything else. Young bats squeak incessantly if the females are away, and this is sometimes enough to drive people "batty." Ectoparasites that live on bats only try to bite people if there are no bats to feed on, i.e., AFTER control measures have been taken. However, where bats are roosting in areas accessible to children or where the owner is not willing to co-exist with bats, control methods can be undertaken.
The ONLY SURE METHOD OF GETTING RID OF BATS IS TO PREVENT THEIR ACCESS TO THE BUILDING. First, locate the entrance holes to the roost. By watching the building at dusk, it is often possible to see exactly where the bats are coming out. During the day, you can look for bat droppings (they look like mouse droppings) stuck on the wall of the building or accumulated in piles on the ground. The entrance to the roost will be somewhere above the droppings. The entrance usually is surrounded by a narrow dark brown oil smear (the oil and dirt rub off the bats as they enter the roost). Bats squeak and rustle as they crawl in the roost and this helps pinpoint exactly where they are located. When searching for entrance holes, remember the rule of thumb — a bat can probably squeeze through any space big enough for your thumb to fit through.
Bat proofing a house may involve screening louvres, vents, chimneys, and large ventilation openings with 6 mm (0.2 in) mesh hardward cloth; closing small cracks in eaves and rafters with caulking compound, sidings or sheet metal; nailing down loose shingles or facings; sealing the joint between the roof and the chimney with sheet metal, cement, or mortar. If mothballs are used, 1.5 to 2.5 kg (3 to 5 lb) should be sprinkled throughout the attic. However, as noted below, mothballs are of limited use for removing bats.
After the bats are driven out, seal the entrances. Close off or seal all openings except one (using screening or caulking). On the outer side of the remaining entrance, place a one-way device (plastic bag with both ends cut out) (see Figure 2). Bats can now get out through the bag, but cannot return. More elaborate devices of slotted tubes and valves achieve the same results. Now, your knowledge of the biology of bats becomes important. Not all bats leave the roost every night. Therefore, if you close off all entrances, some bats will be trapped inside. They may become frantic and in seeking alternative exits, come out inside the building (thus, the plastic bag to let them out).
Attempts to remove bats from buildings should not be conducted in June or July. Young bats, not yet able to fly, will be trapped inside where they will eventually starve. The most common house bat, the little brown, migrates away from buildings each fall. Thus, the wisest course is to wait until October and then plug all the entrances to the roost. When the bats return in spring, they will be unable to get in.
Various other methods have been used to remove bats. These can be grouped into general categories of chemicals (e.g., DDT, fenthion, zinc phosphide, anticoagulants), sticky substances (e.g., Tanglefoot, Tacky Toes), and habitat manipulations (e.g., artificial light, mothballs, ultrasonic rodent repellers, exclusion devices).
Research and field experience consistently show that the application of chemicals or sticky substances generally is ineffective in solving bat problems. The use of chemicals often results in dazed or weakened bats which may be picked up by children or pets. In addition, stress due to sublethal doses may result in a bat becoming more susceptible to infection (e.g., activation of latent rabies infection). All studies indicate that these poisons should NOT be used in attempts to control populations of insectivorous bats.
As bats prefer dark spaces, artificial light has been used successfully to drive bats out of some attics. The light must be kept on continuously and moved regularly. Otherwise the bats soon find dark corners or shadows in which to avoid the light.
Mothballs (paradichlorobenzene), vaporizing pest strips, formalin, and concentrated bleach also have been used successfully. However, these chemicals only work in small areas where the noxious fumes can accumulate. In addition, success is temporary. Once the fumes weaken, the bats will return.
Ultrasonic repellers are ineffective as a deterrent against an animal which uses ultrasound waves in many aspects of its life. They may actually attract bats.
Bats have been persecuted needlessly since the dark ages. In reality, they are an essential link in the balance of nature and an important part of the natural fauna of our province. They provide a valuable service in consuming many flying insects and pose little threat to human health. There is no evidence that widespread destruction of bats or their roosts has reduced the already low health hazard. Control of bats should be done by excluding entry into buildings, not by killing the bats.
Bat Houses
Although
suitable habitat generally is available throughout Alberta, bat houses
can provide an alternative place for bats to live. Unlike bird houses,
only a few bat houses have been successfully colonized in northern
latitudes. Heat is critical to the growth and development of young
bats (faster growth at warmer temperatures) and thus bat houses should
be located in full sun, at least 3 metres above the ground and should
be painted or stained with a dark color. Inner surfaces should be roughened
to make it easier for the bats to hang on. Plans for bat houses are
available here and from the Bat
Conservation International website.
