Arthur M. Greenhall, B.A., M.S., F.L.S.*
Vampire bats, which transmit paralytic rabies, pose a major obstacle to livestock raising in areas extending from Mexico to Argentina. More widespread use of available bat control meas- ures could stop large-scale animal losses and should be con- tinued. However, it is important that the innocuity and safety of recently developed anticoagulant techniques be amply dem- onstrated before the latter become widely used.
Introduction
The Vampire Bat Problem
Restricted to the Western Hemisphere, vam- pire bats pose a unique veterinary public health problem. These bats feed exclusively on the blood of vertebrates, including man, and so in- fected vampires are apt to transmit paralytic rabies and other pathogenic diseases in the course of normal feeding. Aside from this, how- ever, the victims’ loss of blood alone may repre- sent a serious problem.
Vampire bats belo’ng to .the subfamily Desmodontinae of the Neti World Leaf-Nosed Bats, the Phyllostomatidae. There are three known species: Desmodus rotundus, the com- mon vampire bat; Diaemus youngi, the white- winged vampire bat; and Diphylla ecaudata, the hairy-legged vampire bat. All are subject to in- fection with rabies, but Desmodus is the most important transmitter of the disease.
Ever since Latin America was first settled by Europeans, the presence of European-type live- lAn abridged and updated version of the article published in Spanish in Boletin de la Oficina Sanitaria Panamericana, Volume LXXI, No. 3, September 1971, pp. 231-246.
ZFormerly Bat Ecologist, Food and Agriculture Organization, Research ProJect on Paralytic Rabies (FAO MEX 16/UNDP 242), National Institute of Live- stock Research, Palo Alto, Mexico, D.F., Mexico. Pres- ently Research Associate! National Museum of Natural History, The Smithsoman Institution, Washington, D.C. 20560, U.S.A.
stock seems to have offered a more accessible, more plentiful, and perhaps more desirable source of blood than has the native fauna. In any case, Desmodus has increased its numbers and distribution wherever livestock raising has been introduced. Also, manmade structures have provided supplemental roosts for this adaptable mammal. Th& result is that Desmodus and rabies now range together over most of the significant livestock-raising areas from northern Mexico to central Argentina.
Besides spreading disease, nightly attacks by, vampire bats can debilitate livestock and poul- try, often exsanguinating the latter. The milk yield of severely bitten cows drops markedly, and sows bitten on their teats are often unable to nurse their young. Since a single bat may consume a daily average of 20 ml of blood, equivalent to 15 pints per year, and since sev- eral hundred Desmodus may occupy a single roost, predation can be intense.
Moreover, open wounds caused by bat bites and aggravated by anticoagulants in the bats’ saliva will continue to ooze blood for many hours and may attract blood-feeding arthro- pods. Other pathogenic organisms such as trypanosomes may thus enter the prey’s blood- stream after the bats have finished their work
Control
of
Other Bat Specieslinked to control of various non-vampire bat species (2). While these other bats do not attack man and livestock directly, any bat can become diseased, and certain types have become more numerous by adapting their feeding and roost- ing habits to human settlement. Some have even abandoned caves and hollow trees for structures occupied by man or domestic ani- mals, thus increasing the possibility of disease transmission.
In particular, nine non-vampire species fre- quently found infected with rabies should re- ceive close ecological and epidemiologic surveil- lance (3). These bats share certain attributes with vampires: they may be found in the same roost; they are widely distributed throughout the tropics; they sometimes occupy buildings frequented by domestic animals and people; they live in groups or colonies; they have sharp teeth capable of breaking human skin; they can fly considerable distances; they frequently change their roosts; they do not hibernate; and they are beneficial as insect-eaters, plant pol- linators, and seed dispersers. The species in question are as follows: Noctilio leporinus, the fisheating bat; Phyllostomus hastatus, the greater spear-nosed bat; Glossophaga soricina, the long-tongued bat; Carollia perspicillata, the short-tailed fruit bat; Artibeus jamaicensis, the Jamaica fruit bat; Artibeus lituratus, the Trini- dad fruit bat; Tadarida brasiliensis, the Brazil free-tailed or guano bat; Molossus ater, the large free-tailed house bat; and Molossus molossus, the small free-tailed house bat (2, 6).
Techniques of Vampire Bat Control General Considerations
Cost should not be the primary factor upon which a policy of vampire control is based. However, any estimation of cost should include personnel salaries and per diem ,payments, as well as expenditures on transportation, mate- rials, and equipment.
In seeking to protect the cattle of a rabies- prone area, vampire bat control may be a valu- able and necessary adjunct to rabies vaccina-
tion. The latter, after all, cannot prevent bats from biting cattle. To facilitate control where vampires are a serious threat to peasant farm- ing, livestock owners can cooperate with national agricultural authorities in carrying out the control measures desired.
Methods
of
Limited UsefulnessDynamite and poison gas. The use of dyna- mite and poison gas has been discontinued in several countries because these methods tend to be ineffective, nonselective, and dangerous to man. Brazilian authorities have reported that the gas “Rhodiatrox” (a phosphorous-base compound) has destroyed bats in caves when used alone or together with dynamite (4). How- ever, the number of vampires killed was not mentioned.
Argentine authorities have reported using cyanide gas to kill vampires (5), and were it not for the danger to man this gas might be con- sidered useful when Desmodus is found in colo- nies not associated with other bat species. However, the gas clearly poses too great a threat for its users. In July 1972 vampire bat control experiments were being conducted as part of a collaborative control effort by Argen- tina’s Ministry of Agriculture and the Pan Ame- rican Zoonoses Center. The Argentine mam- malogist in charge of the program was inspect- ing the results of fumigating a bat-infested well when his gas mask failed and he died. Rescue efforts were hampered by cyanide gas remain- ing in the well (27).
Smoke and fire: This method must be used cautiously when exterminating bats in hollow trees. If the inside of the tree should ignite, the roost will be completely ruined as a natural trap.
.
candles, kerosene lamps, and many ordinary bulbs have little or no deterrent effect.
Other Established Methods
Electrocution: An elaborate network for electrocuting cave bats has been established in Sao Paulo, Brazil. Unfortunately, besides killing vampires it has also killed large numbers of other bats (9).
Firearms: Shooting vampire bats inside caves or hollow trees and shooting fruit bats out of tall palm trees are practical extermination methods that are used frequently in Trinidad and Tobago. Appropriate weapons include .22 caliber pistols, revolvers, and rifles; shotguns using scatter-shot cartridges; and .410 shotguns using the smallest possible shot sizes (shot numbers 8-l 2).
Strychnine: This method exploits the vam- pires’ habit of returning to feed at fresh wounds made the previous night. If a drop of sugar syrup supersaturated with strychnine sulphate is properly applied to such a wound, it will kill the vampire within seconds after its tongue touches the treated bite. This technique, de- veloped in Trinidad (11), has been used suc- cessfully in Mexico and Brazil on types of live- stock capable of being touched or handled without difficulty. While the method is safe enough for use with animals and poultry, ex- treme care must be taken to make sure this dangerous poison is kept away from un- authorized persons, children, and pets.
Traps: Harp traps are frequently used for capturing vampires roosting in caves, where nets are impractical. Such traps are not damaged as easily as nets, nor do they need constant atten- tion; and the bats may be left in them for some time before being easily removed at leisure (6, 8).
Also, vampire roosts themselves can often be exploited as natural traps. Bats should be col- lected from such roosts at regular intervals, great care being taken to disturb them as little as possible so that they will not desert the site. This is another method being used in Trinidad.
Protective Screening: Metal or plastic screen- ing with openings no larger than 22 mm will effectively prevent vampires and most other bats from entering livestock enclosures or houses, provided the screening is carefully in- stalled and maintained. In Yucatan, Mexico, the practice of using screens to cover natural wells (cenotes) to prevent the bats from using them as roosts has been widely adopted with good results.
Seine and trammel nets: Simple seine and trammel nets with half-inch mesh and soft lay fiber have been used successfully to trap vam- pires at entrances to hollow trees. They have also been effectively deployed across the open- ings of caves, tunnels, mine shafts, culverts, and wells by using some sort of makeshift frame to brace the netting (6).
Mist nets: Japanese nylon mist nets will ef- fectively enmesh vampires if set along suspected flyways and around livestock corrals, huts, dwellings, or shelters in which animals or humans have been attacked by vampire bats. They were first used in Trinidad and Tobago as a control method and have superseded almost all other methods in that country (II). A de- tailed description of mist net rigging, operation, and maintenance, as well as selection of net sites, is provided in the publication Bats and Bat Banding (6).
trying to estimate a vampire population simply by counting bites seen on cattle, because a number of other variables can have an im- portant hidden effect on the results.
Baiting: For reasons that are still unclear, particular animals or persons frequently seem especially attractive to vampire bats. In Trini- dad, vampire bats have been known to bite through burlap sacks which forest workers sometimes use as sleeping bags to protect them- selves from vampire bat attacks. Yet, inexpli- cably, other workers in the same camp sleeping without any protective covering, not even mosquito netting, have gone unmolested (10).
Nets or traps set around animals that are nat- ural attractants are particularly likely to catch vampires. For example, over a period of years hundreds of vampires have been attracted to one certain bull in Trinidad and have been captured in mist nets set around the animal. In another case a rancher in Yucatan, Mexico, arrived at this technique independently and used it with success.
A notable advantage of the trapping, screen- ing, netting, and baiting techniques just de- scribed is that since they are non-chemical con- trol methods they add no pollutants to the ecosystem in which they are used.
Recently Developed Control Methods
Anticoagulants: The 1973 report of the WHO Expert Committee on Rabies (28) notes that Desmodus is sensitive to small amounts of certain anticoagulants such as diphenadione. After inoculation of a single dose into cattle (1 mg per kg body weight of host) the blood of the treated cattle becomes lethal to vampires for at least three days. It has been claimed that in certain areas this treatment has reduced the number of vampire bites by over 90 per cent (20
Another technique is to smear this com- pound (mixed with petroleum jelly) on the backs of vampires captured with mist nets or other devices. These treated bats are then re- leased to return to their roosts and contaminate
others in their colony through physical contact Gw
With regard to this method, the above- mentioned WHO report made the following comment:
The Committee emphasizes that the in- nocuity of this product must be adequately demonstrated in cattle, especially by the lack of harmful residues in meat and milk. . . More- over, it should be noted that vampires roost in wells in some areas and contamination of well water could easily occur. More information is also needed on the safety of anticoagulants to other bat species sharing the same roosts, as . well as to carnivores that may consume dead vampires.
Biological Control: Methods in this category are forms of applied ecology aimed at regula- ting population levels rather than merely destroying individual bats. They strive to re- duce the birth rate or raise the death rate over the long run through increased predation, habitat manipulation, introduction or stimula- tion of epizootics, and application of anti- fertility agents. Perhaps antifertility agents offer the greatest promise-particularly chemo- sterilants which could be applied like the anti- coagulants just mentioned.
Discussion
Only the need for sufficient funds, time, and manpower limits ecological studies capable of providing an adequate basis for control. In general, initial studies of this kind should include: (a) sample capture and identification of bats in order to define the problem, (b) de- termination of the bats’ numbers and popula- tion structure; (c) a banding program, if feasi- ble, to determine vampire bat movements; and (d) recording of bat mortality and predation where possible. Studies intended to be more thorough should also cover significant aspects of the bats’ behavior, distribution, habitats, roosts, food, reproduction, population dy- namics, parasites, predator/prey relationships, and disease.
will probably fall into one of several broad con- trol categories:
1) Chemical control: Development of new attractants, repellants, anticoagulants and other toxicants, stupefacients, anesthetics, or chemosterilants.
2) Physical confrol: Refinement of traps and nets; development of electric devices sensi- tive to motion, shape, color, light, odor, etc.
3) Electronic control: Development of de- vices using sound waves ranging from.very low to very high frequencies which may attract or repel bats.
4) Biological control: Improved habitat manipulation (20); encouragement of preda- tors, parasites (24,), and diseases (19, 21, 22, 23); development of chemosterilants and methods of genetic manipulation (1.5, 16).
In general, promising advances have recently been made in chemical control, so that now, in order to maintain an appropriately varied as- sortment of controls there is a clear need to intensify the search for methods of biological control.
Most methods have special advantages in particular situations, so that each should be used as circumstances dictate. Exceptions to this rule are potentially dangerous new tech- niques, which should not be widely used; rather, they should be used in a limited way in order to ensure their safety without running the risk of unanticipated damage on a fairly large scale. Confirming the safety of such techniques requires a thorough understanding of bat ecol- ogy. Unfortunately, such information about both vampires and other bats is presently scanty or lacking altogether (12, 23, 14).
In general, the ecosystem involved should be considered as a single unit; it should be kept in mind that the minimum vampire bat population level at which the bats cause damage or become a nuisance varies from place to place; no single control technique should be relied upon to provide a satisfactory solution for any given vampire problem; and the innocuity of any chemical used should be clearly proven-
consequences for non-vampire bats living in the same roosts as the vampires and possible sec- ondary hazards for animals which consume poisoned bats.
High-Priority Studies
Estimation of vampire bat populations. At present there is no reliable method for estimat- ing vampire bat populations; and it is essential that such be devised in order to evaluate the results of control programs. Programs are cur- rently assessed subjectively by recording the degree to which the number of vampire bites on livestock are reduced. Besides providing im- portant information, a reliable census method might also help to determine what bat popula- tion density is needed for rabies infection to spread easily among vampires and thence to livestock (29).
Determination of Vampire Bat Host Prefer- ences. Studies dealing with this question should be contmued because the spectrum of livestock and wild animals being preyed upon by vam- pires varies from one area to another. Also, vampire bats are known to occur in areas where no domestic stock exists and are possibly in- volved with wild animals in a sylvatic rabies cycle. Some of these areas are now being opened up to livestock raising for the first time (2.5, 29).
Special Studies by Country and Region
SUMMARY Paralytic rabies transmitted by vampire bats, especially the common vampire bat (Desmodus rotundus), is a major deterrent to the livestock industry in Latin America. The problem be- comes more acute as the countries of the Ame- ricas increase livestock production, particularly since vaccination against rabies offers protec- tion only against the disease, not against re- peated attacks by vampire bats.
Some methods of vampire bat control that have already proven effective should be con- tinued while more effective methods are being developed and tested. It must be emphasized, however, that improved vampire control needs to be based on an ecological approach that will not affect other bat species (many of which are beneficial to man) and that will not have other undesired effects. In particular, the innocuity and safety of newly developed anticoagulant
techniques must be adequately demonstrated before they are widely used.
There is no doubt that the subject of vam- pire bat control affects the survival of other bat species that may be found together with Desmodus in the same roost. Therefore, to- gether with the vampires, these bats need to be given priority study. In addition, more informa- tion is netded about the ecosystem in which Desmodus lives-including more data relating to its population dynamics and host preferences. In this regard it is essential to develop a reliable method for estimating vampire bat populations, in order to evaluate control efforts. In addition, it is important that the vampire bat problem be better defined within each country and in areas involving more than one country, since each area affected has special problems of its own.
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