BATS
NUISANCE OR NECESSITYby Angela Marshall
Organon
home.
Bats have played an essential role
in the evolution of nature's checks and balances for a very long time and
their loss today could compromise the health and the stability of our environment.
The usefulness and resourcefulness of bats are being ignored by our society
because of myths and legends which is resulting in a disservice in improving
our environment.
The history and origin of bats is a
long and undecided one. Bat fossils have been found that date back approxiatemately
50 million years but bats from today still resemble bats from then.
Debate has been triggered whether bats
have evolved from a type of flying fox, squirrel, flying lemurs or shrew
like creatures. Flying lemurs share a unique brain orginization but bats
habitats are closest to that of flying foxes however most scientists point
to shrew like creatures as their ancestors.
Bats are placed in a group of their
own (from other mammals) the Chiroptera which means hand wing. In the Chiroptera
group of mammals there are two types of Chiroptera in which all living
bat species fit. The Megachiroptera are commonly referred to as flying
foxes (because of their fox like faces) and are only found in the Old World
Tropics. The Microchiroptera are highly varied in apperance and are found
all over the world.
Myths and legends that bats are nasty
creatures that kill people by sucking out their blood and turning into
monsters have led most people to fear and destroy these tiny creatures.
In western society, mentioning bats tends to conjure up images of bloodthirsty
vampires, draughty dark castles and evil spirits. In much of the world
they are treated as harbingers of evil, beasts that deliberately tangle
themselves in long hair and consort with supernatural beings such as werewolves
and vampires. They are accused of stealing bacon and of being blind. However
bats do not try to tangle themselves in people's hair, they do not steal
bacon (most bats don't like bacon according to scientists all over the
world that laugh at the strange rumour), nor are they blind.
A visit to the National Bat Conservatory
(the Rockville, M.D. division), I discovered a few things. Bats have a
tendency to get tangled in a person's hair because they think it's a nest
most of the time, and when they try to land on a person's head they accidently
get their tiny little claws tangled in the hair and it scares them. Bats
are very shy creatures that can be very friendly; even trained as pets.
They are warm, soft and furry; not slimy or scaley or cold. When they are
happy, they purr like cats. When bats are trapped inside a house and flying
around, chances are, they are lost and can't find an exit, so if this ever
happens, open a window, don't seal off their exit, and try not to go swinging
things at it because it's probably more frieghtened than you are. Be very
calm if you can, and give time to find it's way out.
The popular misconception that bats
are dirty and dangerous has led to feeling of distrust and hostility in
many parts of the world. Light is commonly used to repel bats at night.
Livestock owners sometimes suspend various objects which swing above cattle
in night breezes to frighten bats. Some Venezuelan cattlemen claim that
a plant called "sabilla" is successfully used to drive away vampire bats;
they also claim that pigeons repel bats and pigeon roosts have been establised.
Smoke and noise are commonly used to flush bats from roosts. Fitter (1968)
reported that more than 700 Brazilian bat caves and certain Panamanian
caves were destroyed by dynamite, killing vampires and other species of
bats that occupied the caves. Spiny branches of cactus suspended from ceilings
in stables and dwellings sometime entangle bats. Even an elaborate network
was installed in some Brazilian caves to electrocute bats. Poisonous gas
and flame throwers was a common method for killing bats in Africa up until
the late 1960's. Abello Fernadez reported success in destroying a colony
of bats by infecting them with a local strain of Newcastle disease that
had caused a great loss in poultry in the area. The colony was said to
have consisted of 5000 vampire bats.
Poisoning bats with pesticides is the
most common means of destruction. Hundreds of bats have been killed by
spraying DDT. In South America, organophosphorous compound was discharched
into caves by the Antirabies Service destroying over 900,000 bats annually
from 1984 to 1987.
Unnessary arousal of hibernating bats
due to the presence of people is another major factor of bat population
decline. Exits are blocked and clubs and firearms are used to kill bats
in their roosts. Housing developments have boomed in North America in areas
causing bats to evacuate their homes.
Little reseach has been done on bats
contributing to diseases by way of bacteria. Two types of salmonella has
been reported by Klite (1965) to be pathogenic to man from feces removed
from Panama bats. Two types of Shigella (Bacillary Dysentery) was isolated
from one of 2112 bats tested in Colombia (Arat et al, 1968). Pasteurella
(Pseudotuberculosis) was reported by McDiarnid (1962)in England and cited
experimental infections have taken place in Africa and Italy. Mycobacterium
(Tuberculosis and Leprosy) have caused deaths in Indian fruit bats held
captive in England in the 1930's however reports of such problems today
are not documented. The source of infection for the bats was unknown. Bartonella
and Grahamella (Bartnellosis) has been documented in Brazil but no form
of this species has been reported pathogenic to man. Leptospira (Leptospirosis)
has been reported many times over in bats mainly in Australia but no evidence
links a transferral to man. Borella (Relapsing Fever) has been cited in
bats from Europe, Africa, South America, and the United States from 1927
to 1968 however, when C.M. Johnson attempted to transmit the disease from
bat to pig in some lengthy experinments in 1936, he was unsuccessful.
Vampire bats are true parasites of
man and domestic animals according Wimsatt and Guerriere. Blood loss caused
by vampire bats has led to debilitation in humans and livestock and usually
results in the death of poultry. Wimsatt and Guerrriere have noted in their
studies that wild vampire bats may drink on the average 20 ml of blood
per day. A single bat thus consume 7.3 liters (15 pints) per year. A moderate
sized colony of vampires consisting of 100 adult individuals would drain
local livestock approxiatemately 730 liters of blood each year.
In mexico vampire bats usually bite
humans on the cheeks over the zygoma and presumably scars result. They
commonly bite the nipples of cows, causing tissue sloughing and obliteration
of the ducts making the animals unproductive and eventually die of lack
of nourishment.
The wound created by a vampire's bite
according to Darwin interferes with the use of saddles on horses and provides
an entry portal for various microbial pathogens and screw worms.
Vampire bats have been found infected
with various agents of disease and in some instances these bats are insrumental
in transmitting them. The most common viruses are foot and mouth disease
virus and yellow fever virus but the one that bats are feared the most
is rabies. Vampire bats have bitten leprosy victims and might spread that
disease and it is not inconceivable that they may spread such diseases
as anthrax, blackleg, hog cholera, glanders, mange, and others.
From medicines to fossil fuels bats
have an can contribute to our society if more people could invest a positive
interest in protecting bats throughout the world. Hibernation or hypothermia
increases the ressistance of the host to various viral, bacterial, protozoan
and metazoan parasites (Kayser). Bats are of special interest in studies
of this nature because as mammals they are more likely to be susceptible
to diseases of man than cold blooded creatures, yet unlike other mammalian
hibernators, many bats can be quickly induced at any season into a metabolic
state resembling hibernation. In these states of hibernation bats were
shown to delay the development of Venezuelan equine encephalitis (Corristan
1958), Japanese Bencephalitis and St. Louis encephalitis (Sulkin 1966),
tickborne viral infection (Nosek 1961), and Coxsackie B 3 viral infection
(Dempster 1961) producing little pathology. Hypothermia at the time of
inoculation may have prevented establishment of rabies viral infections
in bats (Sadler and Endright 1959; Sulkin 1960). Ammonia has been noted
to accumulate in certain bat roosts with concentrations as high as parts
per million, which is 50 times the maximum concentration endurable by man
for 1 hour of exposure. Observations suggested that ammonia decreased the
metabolic rate of Macrotus waterhousii. Carbon Dioxide concentrations are
high in some bat roosts, as high as over 50 times the usual concentration.
This has shown an extraordinary resistence of Myotis to anoxia. The transilluminated
bat wing is an excellent method for observing circulatory and other phonomena
(Nicoll and Webb). Studies of the toxicity of alcohol and alcohol drug
combinations investigating wing vessel responses have proven successful
in discovering complications in humans in this area. Studies in skeletal
muscle regeneration concluded that satellite cells transform into myblasts
that increase in number and ultimately form new muscle fibers. These studies
have been used to study regeneration of damaged nerves in humans. Studies
in which melanocytes could be observed in the wing membrane muscles have
been used to study hormonal alteration and irradiation. Bats have even
been used in studies of cigarette smoke on vasomotion in arterioles of
wing membranes so that scientist could see with much ease what it does
to humans. In addition to being used in epidemiological studies of diseases,
bats may prove useful in several other areas of medical research: (1) Vaccine
development. (2) Space biology, because of bat's abilities to tolerate
temperature extremes and various gases. (3) As experinmental animals in
other stressful environments. (4) The use of hypothermia, hyperthermia,
or various gases in the prevention or therapy of diseases caused by viral,
rickettsial, bacterial, mycotic, and metazoan parasites. (5) The use of
hypothermia in the prevention or therapy of intoxications or radiation
pathology. (6) Mechanisms permitting survival in extremes of population
congestion. (7) The detection of chlorinated hydrocarbons. (8) The transiluminated
wing of the living bat should find additional utilization in the gross
and microscopic observation of physiological or pathological phenomena.
(9) As a bioholographic model, the bat may enable disclosure of natural
methods of information processing and storage in the brain and how these
processes may be influenced.
Knowledge gained from studies of echolocation
in bats has been used to make devices that perform a similar function for
blind people. The ablilty of bats that perceive objects by sound exceed
conventional echolocation because they can distinguish between objects
of different shapes. Greguss reported that the bioholographic method (memory
data may be stored in holographic form) may not be restricted to bats and
that it may function in humans.
Like most mammals, bats can contract
rabies; however it is a common misconception that most bats are rabid.
This impression stems from early studies that seemed to show that unlike
other animals, bats could contract rabies and transmit the disease over
long periods of time and not show any signs of illness themselves. The
presumption that they were asymptomatic carriers of rabies received worldwide
publicity and quickly became a fact in everyone's mind. Over 20 years of
research now shows that less than a half of 1 percent of bats contract
rabies which is no higher than that seen in other animals, but unlike dogs
and cats rabid bats seldom become aggressive.
Guano can be a major resource in our
world but has been ignored over the past 70 years. Guano and guano enriched
soil have been used throughout warm ares of the world as sources of saltpeter
for the production of gunpowder. Bat guano is still a valuable source of
organic fertilizer in many parts of the world. Guano can even be used for
fossil fuels to run car engines.
Third world countries use dangerous
pesticides to kill insects that spread disease not realizing that the very
same bats that they kill could one day be controlling the population of
harmful insects. It is evident that insectivorous bats consume enormous
numbers of anthropods. R.B. Davis noted that capturing a bat returning
to it's cave in Texas it's stomach contents weighed 1 gm more than on it's
departure earlier. Taking this as the nightly consumption of insects, scientists,
extrapolated to a population of 50 million bats feeding an average of 120
nights per vernal cycle in Texas and obtained a total of 6600 tons of insects
per year in Texas. Gould (1955) found that some adult bats captured insects
at an estimated rate of up to 500 anthropods per hour feeding mostly from
moths, small flies and mosquitoes. Ross (1967) did a remarkable study on
the food habits of insectivorous bats discovering two methods bats capture
their prey: (1) Filter feeding whereby dense groups of prey, possibly found
by echolocation are attacked in flight; (2)individual pursuit, also possibly
found by echolocation, whereby individual insects are approached then attacked
from the rear. In Ross's studies size had a major factor and bats that
preferred the filter feeding method usually injested smaller insects. In
his conclusions, Ross stated that the apparant preference of different
bat species for particular groups of arthropods provides encouragement
that bats exert some control over these arthopods. Thus, one species of
bat may keep down numbers of gnats and mosquitoes, whereas another species
of bat may control moths or beetles. The incident at Eagle Creak Cave were
there was over a 99.9 percent decline in population in a three year span
ment more than 350,000 pounds of insects went uneaten nightly, inexorably
upsetting nature's balance.
The removal of bats from the wild for
scientific and educational purposes, as well as for food and and just to
clear land for more space for people has to be controled. By 1978, two
North American species, Grey and Indiana Bats were listed as officially
endangered because of human population growth. In 1963, the world's largest
known bat colony, close to 30 million Mexican free tails lived in Eagle
Creek, Arizona. In just six years their numbers were reduced to 30,000
which was a 99.9 percent decline. Major population losses are documented
on all continents. Flying foxes, have recently become extinct without being
declared endangered.
Although bats have a reputation as
far as diseases go that is very hard to fight the work that they have and
can help us achieve in the medical field is too great to ignore. Along
with the endangerment and extinction of some species of bats, we should
look at the cruel and unnessary methods of using and abusing these creatures
and find alternative methods for controling them. Negative attitudes must
be replaced with an understanding of the ecological, economic, and scientific
value of bats. This goal can be achieved through education.
Bibliography:
Dalquest, W.W. "Natural history of
the Vampire bats of eastern Mexico." American Midland Nature, 1955, 53,
7987
Darwin, Charles R., "Journal of Researches
into the Natural History and Geology of the Countries Visited during the
Voyage of the H.M.S. Beagle," Routledge, England. 1891
Fenton, Brock, "Just Bats." Canada:
University of Toronto Press, 1983.
Geluso, Kenneth, N., J. Scott Altenbach,
Ronal C. Kerbo, "Bats of Carlsbad Caverns National Park." Carlsbad,
New Mexico: Carlsbad Caverns Natural
History Association, 1987
Greguss, P., "Bioholography," Nature.
1968, 219
Nowak, Ronald M. "Walker's Bats of
the World." Baltimore, M.D.: The Johns Hopkins University Press, 1994.
Turner, Dennis C. "The Vampire Bat."
Baltimore, Maryland: The Johns Hopkins University Press, 1975.
Tuttle, Merlin D. "America's Neighborhood
Bat's." Austin, Texas: The University of Texas Press, 1988.
Wimsatt, William A. "Biology of Bats
Volume II." New York, New York: Academic Press, 1970.
Yalden, D.W., P.A. Morris. "The Lives
of Bats." New York, New York: Quadrangle/ The New York Times Book Company
, 1975.
This page copyright © 1997
Angela Marshall.