Northern Prairie Wildlife Research Center
Some public antipathy to bats, especially when they become a nuisance in houses, derives from phobias based upon myths. To many people bat prejudice suggests that the answer to problem bats is a bat toxicant. According to Constantine (1979a) "Killing the bats is contraindicated. This is true for a variety of reasons: (1) It is a waste of time, because the animals usually are replaced promptly by other bats; (2) Killing the bats has the effect of displacing the only permanent solution, which is physical exclusion; (3) Killing the bats is hard to justify, because the incidence of rabies infection is extremely low, and the animals are of value in insect control; (4) But the killing of bats is contraindicated primarily because the toxins likely to be used, such as DDT, scatter sick bats over wide geographic areas (Greenhall and Stell 1960) where persons and pets can be bitten as they investigate them."
The rationale for the use of chemicals to control bats in buildings has been the fear of human exposure to rabid bats. The effects of organochlorine insecticides applied to bats, their roosts, or both, to kill them has been reviewed by Clark (1981b).
During the late 1940's, DDT became a popular toxicant for bat control (Luckens and Davis 1964). The FWS held a registration for DDT (50% wettable powder) for bat control from 10 June 1966 to 12 October 1970. The FWS terminated the use of DDT and its recommendation on 2 July 1970. Two years later, EPA placed a general prohibition on the use of DDT except where certain public health hazards exist. Thus, DDT is the only chemical federally registered by EPA (Registration Number 36765- 1) as a toxicant for bat control and it is necessary to obtain special approval for its use from CDC (Anonymous 1975).
On 28 May 1976, CDC became the agency responsible for the issuance of DDT for the control of bats inside buildings, where they constitute a demonstrated rabies health hazard. DDT can be used only by agencies approved by CDC. Only after practical alternative methods have failed will CDC provide, on approval of a request, one 300-g (10.5-oz) package of 75% DDT wettable powder (CDC no date; Lera and Fortune 1978).
Residues of DDT are known to be highly toxic to bats. This compound was evaluated by Greenhall and Stell (1960) who found that it killed bats for at least 1 year. These authors found that bats were poisoned and scattered for as long as 4 years after an application (unpublished observations). Kunz et al. (1977) studied the mortality of a little brown bat colony following multiple applications of DDT and clordane, noting persistent kill for more than 4 years. Kunz revisited the roost in 1979 and found that DDT continued to kill bats 6 years later (personal communication). Barclay et al. (1980) quantitatively compared the effectiveness of DDT, sticky deterrents, and sealing access routes for controlling colonies of big brown bats in buildings. Their results confirmed those of Kunz et al. (1977) that the use of DDT is ill-advised. Lethal bat contacts could continue for years after the poisons have been applied; also, bat-human contacts increased after treatment. Trimarchi (1978) suggested that physiological stress could activate latent rabies virus and sublethal doses of pesticides may increase the local incidence of rabid bats. Barclay et al. (1980) stated, "this situation constitutes a strong argument against the use of pesticides to control bats."
There are other obvious and serious human health hazards, such as carcinogens, associated with the use of a persistent toxicant (DDT), in the closed areas of a home. In a loosely constructed building, DDT, whether used as a spray, dust, or powder can seep down into the living quarters. Since DDT is highly persistent (more than 30 years; Pimentel 1971), it is conceivable that an old bat roost regularly treated with DDT and later dismantled could be harmful to humans.
In discussing the testing of vertebrate pesticides for use in disease control Beck and Jackson (1977) stated, "The use of DDT or other chlorinated hydrocarbon sprays against rabid bats is perhaps the worst possible approach. These methods also disperse the colony, cause lingering mortality just as the disease does, and increase human contacts and the attendant panic with an often inaccurate press."
A recent technique reported by Clark (1981a) enables the accurate diagnosis of deaths of bats from organochlorine pesticides on the basis of residues in carcass fat. The technique is thus applicable for use with bats whose brains were removed for rabies testing before the possibility of pesticide poisoning had been considered.
Although no anticoagulant is federally registered by EPA for bat control, a powdered anticoagulant (chlorophacinone) has been registered for rodents and can be registered by individual States for restricted use under Section 24(c) "Special Local Needs," (SLN) of the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) as amended (EPA 1976). Nevertheless, the hazardous nature of chlorophacinone for house bat control was demonstrated in a major prosecution of a Minnesota pest control operator for the misuse of Rozol in bat control work (EPA 1980). In a wideranging, 50-page opinion, Judge Marvin E. Jones ruled on 8 May 1990 that the use of Rozol for bat control constituted a public health hazard.
Constantine (1979a), who testified on behalf of EPA, made the following comments on the use of chlorophacinone dust to kill bats: "This method was similarly unproductive, accounting for the destruction of not more that ten percent (usually far less) of resident bats, despite applications of massive amounts of the material to attic ceilings and walls. In addition to scattering sick bats, this method endangers the public health to an alarming extent by exposing house occupants to the anticoagulant through contact, inhalation, or ingestion through contamination of food. Furthermore, the cat that brings the contaminated poisoned bat into the house will get anticoagulant in its mouth, and the child, parent, animal control officer, and laboratory workers who handle poisoned bats can be expected to get the material on their hands. Like products have passed through the skin." Constantine also noted that the uses of anticoagulants would present similar problems of increased human contact with moribund bats as with other slow-killing pesticides such as DDT. The recognition and treatment of anticoagulant poisoning is described by Morgan (1976).
Although some fumigants (methyl bromide, hydrocyanic acid, and sulfuryl fluoride) have directions for fumigating entire buildings, none of these highly toxic chemicals, which can be applied only by trained professionals, are currently registered for bat control. Such pesticides should be considered for bat control only in a real public health emergency, as established by the appropriate State or City health officials, and only after all other feasible methods have been tried and failed. Treatment of fumigant poisoning is described by Morgan (1977).