VAMPIRE CONTROL IN THE AMERICAS: A REVIEW AND PROPOSED PROGRAM FOR ACTION’

Arthur M. Greenhall, B.A., M.S., F.L.S.*

Vampire , which transmit paralytic rabies, pose a major obstacle to livestock raising in areas extending from to . More widespread use of available bat control meas- ures could stop large-scale 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 stock seems to have offered a more accessible, more plentiful, and perhaps more desirable The Problem source of blood than has the native fauna. In any case, has increased its numbers Restricted to the Western Hemisphere, vam- and distribution wherever livestock raising has pire bats pose a unique veterinary public health been introduced. Also, manmade structures problem. These bats feed exclusively on the have provided supplemental roosts for this blood of vertebrates, including man, and so in- adaptable . Th& result is that Desmodus fected vampires are apt to transmit paralytic and rabies now range together over most of the rabies and other pathogenic diseases in the significant livestock-raising areas from northern course of normal feeding. Aside from this, how- Mexico to central Argentina. ever, the victims’ loss of blood alone may repre- Besides spreading disease, nightly attacks by, sent a serious problem. vampire bats can debilitate livestock and poul- Vampire bats belo’ng to .the subfamily try, often exsanguinating the latter. The milk Desmodontinae of the Neti World Leaf-Nosed yield of severely bitten cows drops markedly, Bats, the Phyllostomatidae. There are three and sows bitten on their teats are often unable known species: Desmodus rotundus, the com- to nurse their young. Since a single bat may mon vampire bat; Diaemus youngi, the white- consume a daily average of 20 ml of blood, winged vampire bat; and Diphylla ecaudata, the equivalent to 15 pints per year, and since sev- hairy-legged vampire bat. All are subject to in- eral hundred Desmodus may occupy a single fection with rabies, but Desmodus is the most roost, predation can be intense. important transmitter of the disease. Moreover, open wounds caused by bat bites Ever since Latin America was first settled by and aggravated by anticoagulants in the bats’ Europeans, the presence of European-type live- saliva will continue to ooze blood for many hours and may attract blood-feeding arthro- lAn abridged and updated version of the article pods. Other pathogenic organisms such as published in Spanish in Boletin de la Oficina Sanitaria Panamericana, Volume LXXI, No. 3, September 1971, trypanosomes may thus enter the prey’s blood- pp. 231-246. stream after the bats have finished their work 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- Control Other Bat Species ently Research Associate! National Museum of Natural of History, The Smithsoman Institution, Washington, D.C. 20560, U.S.A. The subject of vampire bat control is closely

30 Greenhall . VAMPIRE BAT CONTROL IN THE AMERICAS 31

linked to control of various non-vampire bat tion. The latter, after all, cannot prevent bats species (2). While these other bats do not attack from biting cattle. To facilitate control where man and livestock directly, any bat can become vampires are a serious threat to peasant farm- diseased, and certain types have become more ing, livestock owners can cooperate with numerous by adapting their feeding and roost- national agricultural authorities in carrying out ing habits to human settlement. Some have the control measures desired. even abandoned caves and hollow trees for structures occupied by man or domestic ani- mals, thus increasing the possibility of disease Methods of Limited Usefulness transmission. In particular, nine non-vampire species fre- Dynamite and poison gas. The use of dyna- quently found infected with rabies should re- mite and poison gas has been discontinued in ceive close ecological and epidemiologic surveil- several countries because these methods tend to lance (3). These bats share certain attributes be ineffective, nonselective, and dangerous to with vampires: they may be found in the same man. Brazilian authorities have reported that roost; they are widely distributed throughout the gas “Rhodiatrox” (a phosphorous-base the tropics; they sometimes occupy buildings compound) has destroyed bats in caves when frequented by domestic and people; used alone or together with dynamite (4). How- they live in groups or colonies; they have sharp ever, the number of vampires killed was not teeth capable of breaking human skin; they can mentioned. fly considerable distances; they frequently Argentine authorities have reported using change their roosts; they do not hibernate; and cyanide gas to kill vampires (5), and were it not they are beneficial as insect-eaters, plant pol- for the danger to man this gas might be con- linators, and seed dispersers. The species in sidered useful when Desmodus is found in colo- question are as follows: Noctilio leporinus, the nies not associated with other bat species. fisheating bat; hastatus, the However, the gas clearly poses too great a greater spear-nosed bat; soricina, threat for its users. In July 1972 vampire bat the long-tongued bat; perspicillata, the control experiments were being conducted as short-tailed fruit bat; jamaicensis, the part of a collaborative control effort by Argen- Jamaica fruit bat; Artibeus lituratus, the Trini- tina’s Ministry of Agriculture and the Pan Ame- dad fruit bat; Tadarida brasiliensis, the rican Zoonoses Center. The Argentine mam- free-tailed or guano bat; Molossus ater, the large malogist in charge of the program was inspect- free-tailed house bat; and Molossus molossus, ing the results of fumigating a bat-infested well the small free-tailed house bat (2, 6). when his gas mask failed and he died. Rescue efforts were hampered by cyanide gas remain- Techniques of Vampire Bat Control ing in the well (27). Smoke and fire: This method must be used General Considerations cautiously when exterminating bats in hollow trees. If the inside of the tree should ignite, the Cost should not be the primary factor upon roost will be completely ruined as a natural which a policy of vampire control is based. trap. However, any estimation of cost should include Artificial illumination: Some ranchers in personnel salaries and per diem ,payments, as Mexico and elsewhere have frustrated vampire well as expenditures on transportation, mate- attacks by providing flood-lighting or other rials, and equipment. bright illumination for cattle corrals and swine In seeking to protect the cattle of a rabies- enclosures. Other livestock owners, however, prone area, vampire bat control may be a valu- have abandoned this practice. Despite these able and necessary adjunct to rabies vaccina- mixed results, it is clear that the weak light of 32 PAHO BULLETIN . Vol. VIII, No. I, 1974 . candles, kerosene lamps, and many ordinary Protective Screening: Metal or plastic screen- bulbs have little or no deterrent effect. ing with openings no larger than 22 mm will effectively prevent vampires and most other bats from entering livestock enclosures or Other Established Methods houses, provided the screening is carefully in- stalled and maintained. In Yucatan, Mexico, the Electrocution: An elaborate network for practice of using screens to cover natural wells electrocuting cave bats has been established in (cenotes) to prevent the bats from using them Sao Paulo, Brazil. Unfortunately, besides killing as roosts has been widely adopted with good vampires it has also killed large numbers of results. other bats (9). Firearms: Shooting vampire bats inside caves Seine and trammel nets: Simple seine and or hollow trees and shooting fruit bats out of trammel nets with half-inch mesh and soft lay tall palm trees are practical extermination fiber have been used successfully to trap vam- methods that are used frequently in Trinidad pires at entrances to hollow trees. They have and Tobago. Appropriate weapons include .22 also been effectively deployed across the open- caliber pistols, revolvers, and rifles; shotguns ings of caves, tunnels, mine shafts, culverts, and using scatter-shot cartridges; and .410 shotguns wells by using some sort of makeshift frame to using the smallest possible shot sizes (shot brace the netting (6). numbers 8-l 2). Mist nets: Japanese nylon mist nets will ef- Strychnine: This method exploits the vam- fectively enmesh vampires if set along suspected pires’ habit of returning to feed at fresh wounds flyways and around livestock corrals, huts, made the previous night. If a drop of sugar dwellings, or shelters in which animals or syrup supersaturated with strychnine sulphate humans have been attacked by vampire bats. is properly applied to such a wound, it will kill They were first used in Trinidad and Tobago as the vampire within seconds after its tongue a control method and have superseded almost touches the treated bite. This technique, de- all other methods in that country (II). A de- veloped in Trinidad (11), has been used suc- tailed description of mist net rigging, operation, cessfully in Mexico and Brazil on types of live- and maintenance, as well as selection of net stock capable of being touched or handled sites, is provided in the publication Bats and without difficulty. While the method is safe Bat Banding (6). enough for use with animals and poultry, ex- The mist-net method of vampire control has treme care must be taken to make sure this been evaluated at two sites in Mexico: at a dangerous poison is kept away from un- government cattle ranch in the State of Puebla authorized persons, children, and pets. and at a privately owned dairy ranch in the Traps: Harp traps are frequently used for State of Oaxaca. Between May and October of capturing vampires roosting in caves, where nets 1969 respective totals of 5 16 and 182 vampires are impractical. Such traps are not damaged as were netted and removed from these two sites. easily as nets, nor do they need constant atten- To check the efficiency of the method, bat tion; and the bats may be left in them for some bites on cattle were counted before and after time before being easily removed at leisure (6, capture. On the government ranch predation 8). was reduced more than 80 per cent following Also, vampire roosts themselves can often be removal of the 5 16 vampires, and the relief exploited as natural traps. Bats should be col- provided lasted almost a year. On the private lected from such roosts at regular intervals, ranch there was a 75 per cent reduction in vam- great care being taken to disturb them as little pire attacks after removal of the 182 vampires, as possible so that they will not desert the site. and relief lasted six months (7). It should be This is another method being used in Trinidad. pointed out that great care must be used in Greenhall . VAMPIRE BAT CONTROL IN THE AMERICAS 33 trying to estimate a vampire population simply others in their colony through physical contact by counting bites seen on cattle, because a Gw number of other variables can have an im- With regard to this method, the above- portant hidden effect on the results. mentioned WHO report made the following Baiting: For reasons that are still unclear, comment: particular animals or persons frequently seem The Committee emphasizes that the in- especially attractive to vampire bats. In Trini- nocuity of this product must be adequately demonstrated in cattle, especially by the lack of dad, vampire bats have been known to bite harmful residues in meat and milk. . . More- through burlap sacks which forest workers over, it should be noted that vampires roost in sometimes use as sleeping bags to protect them- wells in some areas and contamination of well selves from vampire bat attacks. Yet, inexpli- water could easily occur. More information is cably, other workers in the same camp sleeping also needed on the safety of anticoagulants to other bat species sharing the same roosts, as . without any protective covering, not even well as to carnivores that may consume dead mosquito netting, have gone unmolested (10). vampires. Nets or traps set around animals that are nat- Biological Control: Methods in this category ural attractants are particularly likely to catch are forms of applied ecology aimed at regula- vampires. For example, over a period of years ting population levels rather than merely hundreds of vampires have been attracted to destroying individual bats. They strive to re- one certain bull in Trinidad and have been duce the birth rate or raise the death rate over captured in mist nets set around the animal. In the long run through increased predation, another case a rancher in Yucatan, Mexico, habitat manipulation, introduction or stimula- arrived at this technique independently and tion of epizootics, and application of anti- used it with success. fertility agents. Perhaps antifertility agents A notable advantage of the trapping, screen- offer the greatest promise-particularly chemo- ing, netting, and baiting techniques just de- sterilants which could be applied like the anti- scribed is that since they are non-chemical con- coagulants just mentioned. trol methods they add no pollutants to the ecosystem in which they are used. Discussion

Recently Developed Control Methods Only the need for sufficient funds, time, and manpower limits ecological studies capable of Anticoagulants: The 1973 report of the providing an adequate basis for control. In WHO Expert Committee on Rabies (28) notes general, initial studies of this kind should that Desmodus is sensitive to small amounts of include: (a) sample capture and identification certain anticoagulants such as diphenadione. of bats in order to define the problem, (b) de- After inoculation of a single dose into cattle (1 termination of the bats’ numbers and popula- mg per kg body weight of host) the blood of tion structure; (c) a banding program, if feasi- the treated cattle becomes lethal to vampires ble, to determine vampire bat movements; and for at least three days. It has been claimed that (d) recording of bat mortality and predation in certain areas this treatment has reduced the where possible. Studies intended to be more number of vampire bites by over 90 per cent thorough should also cover significant aspects (20 of the bats’ behavior, distribution, habitats, Another technique is to smear this com- roosts, food, reproduction, population dy- pound (mixed with petroleum jelly) on the namics, parasites, predator/prey relationships, backs of vampires captured with mist nets or and disease. other devices. These treated bats are then re- Insofar as improvement of present control leased to return to their roosts and contaminate methods are concerned, these improvements 34 PAHO BULLETIN . Vol. VIII, No. I, 1974 will probably fall into one of several broad con- consequences for non-vampire bats living in the trol categories: same roosts as the vampires and possible sec- ondary hazards for animals which consume 1) Chemical control: Development of new poisoned bats. attractants, repellants, anticoagulants and other toxicants, stupefacients, anesthetics, or chemosterilants. High-Priority Studies 2) Physical confrol: Refinement of traps Estimation of vampire bat populations. At and nets; development of electric devices sensi- present there is no reliable method for estimat- tive to motion, shape, color, light, odor, etc. ing vampire bat populations; and it is essential 3) Electronic control: Development of de- that such be devised in order to evaluate the vices using sound waves ranging from.very low results of control programs. Programs are cur- to very high frequencies which may attract or rently assessed subjectively by recording the repel bats. degree to which the number of vampire bites on 4) Biological control: Improved habitat livestock are reduced. Besides providing im- manipulation (20); encouragement of preda- portant information, a reliable census method tors, parasites (24,), and diseases (19, 21, 22, might also help to determine what bat popula- 23); development of chemosterilants and tion density is needed for rabies infection to methods of genetic manipulation (1.5, 16). spread easily among vampires and thence to In general, promising advances have recently livestock (29). been made in chemical control, so that now, in Determination of Vampire Bat Host Prefer- order to maintain an appropriately varied as- ences. Studies dealing with this question should sortment of controls there is a clear need to be contmued because the spectrum of livestock intensify the search for methods of biological and wild animals being preyed upon by vam- control. pires varies from one area to another. Also, Most methods have special advantages in vampire bats are known to occur in areas where particular situations, so that each should be no domestic stock exists and are possibly in- used as circumstances dictate. Exceptions to volved with wild animals in a sylvatic rabies this rule are potentially dangerous new tech- cycle. Some of these areas are now being niques, which should not be widely used; opened up to livestock raising for the first time rather, they should be used in a limited way in (2.5, 29). order to ensure their safety without running the risk of unanticipated damage on a fairly large Special Studies by Country and Region scale. Confirming the safety of such techniques Ideally, the vampire bat problem should be requires a thorough understanding of bat ecol- studied regionally rather than just nationally, ogy. Unfortunately, such information about since bats live in specialized environments both vampires and other bats is presently which cross political boundaries. The following scanty or lacking altogether (12, 23, 14). countries and other political units have re- In general, the ecosystem involved should be ported using vampire bat control programs: Ar- considered as a single unit; it should be kept in gentina, Belize, Bolivia, Brazil, Colombia, El mind that the minimum vampire bat population Salvador, Guatemala, Mexico, Trinidad and To- level at which the bats cause damage or become bago, and Venezuela. In large countries, where a nuisance varies from place to place; no single it is impractical for bat control teams to cover control technique should be relied upon to the entire national territory, individual teams or provide a satisfactory solution for any given control officers may wish to instruct and advise vampire problem; and the innocuity of any interested livestock owners and associations chemical used should be clearly proven- about the various safe methods appropriate for particularly with respect to possible undesirable particular situations. Greenhall . VAMPIRE BAT CONTROL IN THE AMERICAS 35

SUMMARY

Paralytic rabies transmitted by vampire bats, techniques must be adequately demonstrated especially the (Desmodus before they are widely used. rotundus), is a major deterrent to the livestock There is no doubt that the subject of vam- industry in Latin America. The problem be- pire bat control affects the survival of other bat comes more acute as the countries of the Ame- species that may be found together with ricas increase livestock production, particularly Desmodus in the same roost. Therefore, to- since vaccination against rabies offers protec- gether with the vampires, these bats need to be tion only against the disease, not against re- given priority study. In addition, more informa- peated attacks by vampire bats. tion is netded about the ecosystem in which Some methods of vampire bat control that Desmodus lives-including more data relating to have already proven effective should be con- its population dynamics and host preferences. tinued while more effective methods are being In this regard it is essential to develop a reliable developed and tested. It must be emphasized, method for estimating vampire bat populations, however, that improved vampire control needs in order to evaluate control efforts. In addition, to be based on an ecological approach that will it is important that the vampire bat problem be not affect other bat species (many of which are better defined within each country and in areas beneficial to man) and that will not have other involving more than one country, since each undesired effects. In particular, the innocuity area affected has special problems of its own. and safety of newly developed anticoagulant

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