Northern Prairie Wildlife Research Center
Commenting generally on chemical repellents, D. G. Constantine (personal communication) stated,
Whereas there is an occasional need for properly applied chemical repellents, the need can be eclipsed by the problems that develop if the chemicals are misapplied. Unfortunately, circumstances usually guarantee that liquid repellents (usually sprays) are applied directly on the bats instead of on surfaces where they land. This has been observed to cause the affected bats to be grounded (after scattering, for miles around in some cases), presenting a far worse problem. This points up a need for delivery of fumes rather than liquid in most instances. As in plugging access holes, one is limited to the late summer and early fall for application; otherwise, young flightless bats may be flushed (spring through mid-summer), or lethargic bats may be expelled (late fall and winter). Properly controlled, the latter procedure may be indicated in some expertly handled instances. In the vast majority of cases, the use of chemical repellents is superfluous, the desired results being achievable by plugging accesses. Moreover, chemical repellents are only temporarily effective.
As of January 1981, naphthalene (crystals or flakes) is the only chemical registered by the Environmental Protection Agency (EPA) as a bat repellent for indoor roosts (EPA registration Number 462-19). Naphthalene should be spread on the floor or applied between the walls, using about 2.3 kg (5 lb) for every 60 m³ (2,000 ft³) which should be adequate to treat an average attic (EPA 1972). As the crystals or flakes vaporize, bats may be repelled. Heavier dosages, 4.5 kg (10 lb), may dislodge bats in broad daylight within a few minutes after introduction. The bats do not return so long as the strong odor remains, but will return when it dissipates. If necessary, the application may be repeated. Its efficacy is greatest when used in confined air spaces. Humans should avoid its inhalation and sensitive individuals are cautioned against all contact (Morgan 1977).
In Canada, Laidlow and Fenton (1971) reported that a bat nursery was substantially reduced by artificial light. Floodlights strung through an occupied attic to illuminate all bat roosting sites may cause bats to leave and seek a new location. Large attics may require four or more 100-watt bulbs. A 150-watt spotlight is more effective. Fluorescent bulbs may also be used to illuminate dark areas.
The size of colonies in the roofs of nine Canadian houses decreased by up to 90% when they were subjected to constant illumination, whereas two unlit control colonies increased by 57 and 97%, respectively. In some situations it is difficult and costly to adequately light a roosting location. Illumination is cleaner than other methods and safer for both humans and bats.
In open spaces where illumination might not work, the area may be made more undesirable for bats if it is possible to open doors and windows or otherwise create drafts. Carefully directed breezes produced by electric fans have successfully repelled bats according to Constantine (1979a).
High-frequency sound has been used to repel or disperse bats. Hill (1970) connected 12 adjustable high-frequency (about 4,000 to 18,000 cps) dog-training whistles to oxygen cylinders located at various points in buildings at a nuclear power station. After 48 h of continuous operation 500 to 1,000 bats (species not mentioned) no longer occupied the building. Three dog whistles attached to a large aquarium pump also had a repellent effect on bats. It is believed that the high-frequency sound waves somehow either interfere with the bats' ability to navigate or otherwise disturbs them. Constantine (1970) mentioned that persons in the vicinity of the ultra-sound emissions became irritable and nervous.
Claims have been made that some variable frequency ultrasonic devices used for rodent control are highly effective against bats. However, Hurley and Fenton (1980) stated that ultrasonic rodent repellents they tested for the control of little brown bats were not effective.
The FWS has initiated research on auditory repellents. In 1974 a sonic device, the EI-700-A Bat-I-Cator, was evaluated in Maine, New Hampshire, and Massachusetts (J. W. Peterson, personal communication). This device emits an intermittent high-pitched "beep" which it was hoped would repel bats from structures. It was tested in about 10 different sites. Peterson said, "In all cases, it was evident that the Bat-I-Cator did agitate, confuse and disorient the bats causing them to fly more erratically and to relocate away from the machine. Bat counts before and after using the machine did not indicate any appreciable reduction in numbers."
The EPA tested a number of rodent electromagnetic repellers which were removed from the market because they did not work for bats as claimed (Smith 1979).
Distress cries of bats can be used to attract other bats to nets or traps. Little brown bats and big brown bats responded to their own distress cries but not the cries of other bat species (Fenton et al, 1976). The authors emphasized the importance of ultrasonics but it is evident that a great deal is unknown about the role of vocalizations in bat behavior.
Sticky-type repellents, such as rodent glue boards, Roost-No-More, Tanglefoot, and Tacky Toes have been used in situations where roost surfaces and bat accesses may be coated. These glue substances may have to be replenished from time to time because dust causes them to lose their tackiness (Marsh and Howard 1977). Barclay et al. (1980) compared three methods used for controlling bats in buildings: use of sticky deterrents, DDT, and sealing access routes used by bats. They evaluated the effectiveness of two sticky deterrents applied around entrances to colonies of big brown bats roosting in three buildings; Tacky Toes was applied as a paste in a 2-cm- (0.8 in.) wide, 0.5-cm- (0.2 in.) thick band onto masking tape surrounding each known access hole at two colonies, whereas Tanglefoot was applied in a 5- to 8-cm-(2- to 3.2-in.) wide coat around and inside the access routes used by bats at one colony. They found that "Sticky deterrents were the least successful, presumably because the bats were able to avoid the substances and because movement of the animals over the treated surfaces presumably reduced their effectiveness. Although repeated applications might have proved more successful, this method is no easier and is less permanent than sealing entrance and exit holes."