Outback Info (Private Seiten) © seit 1999
Australia's Venomous Snakes: The Modern Myth or Are You A Man Or A Mouse?
by Brian Bush
Author's Note: When concerning reptiles, the terms poisonous and venomous
require redefining.
Poison is toxic if inhaled or ingested. The only poisonous reptiles known in
Australia are the Green Turtle and the Hawksbill Turtle. More people have
probably died on this earth as a result of consuming turtle flesh than ever has
been the case from snakebite in Australia. There are no reported deaths from
turtle poisoning here since 1945.
Venom is generally harmless if ingested but toxic when it comes in contact
with the underlying tissue normally protected by the skin. Venomous animals have
to break the skin with body-spines, stings or teeth (includes fangs in spiders
and centipedes). The only venomous reptiles found in Australia are snakes.
For too long we have been telling the world, as well as each other, that
Australia's snakes are the most venomous. On what evidence do we make this
assumption? Solely on their ability to kill mice! What a joke!
The basis for the following discussion and points of view are personal
experience, comments heard and questions asked during my time lecturing on
venomous animals as well as a perusal of the relevant literature. I might just
mention here that I have never lectured to mice!
I have heard it said many times by people I believe should know better that
this or that Australian snake is "more deadly", "more toxic" or "more venomous"
than the Indian Cobra (Naja naja). This is a misrepresentation of the facts and
gains little support from the evidence available concerning humans. These types
of statements have no place in education if positive results are the goal. All
venomous snakes have the potential to be dangerous because of the variable
sensitivity between individual people to venoms. However, first a bite has to
occur.
Australian snakes are inoffensive and very shy. They have had only forty
thousand years of human predation to contend with. None of their behaviour has
evolved targeting humans. The traditional Aboriginal people only harvested the "quiet"
nonvenomous snakes, rarely were the "cheeky" venomous species taken. Maybe this
is why it is almost impossible to accidentally get bitten by one unless you run
around the scrub in bare feet with your eyes shut, and half full on alcohol.
On other continents humans have existed for hundreds of thousands of years.
Therefore, has the cobra evolved the hood, elevated stance and, in some species,
the ability to "spit" venom as a direct response to human predation? What about
the snakes that play dead? The Ringhals (Hemachatus haemachatus), one of a few "cobras"
capable of spitting, also plays dead. This behaviour would have little effect in
deterring a predator looking for a feed, but it may deter a passing human from
taking up a club and clobbering the snake into lifeless pulp.
There is a widespread misconception that our snakes are very dangerous
animals. Many of us do little to dispel this belief, maybe because we like to
believe that Australia's snakes are the most dangerous. This is definitely the
modern myth!
In the past 35 odd years I have met many people who believe tiger snakes have
chased them. However, I have yet to meet someone that has been caught by one!
I often publicly comment that Australia's snakes are the deadliest in the
world if you are a mouse. This is an objective statement supported by the
available data. See Figure 1 for a true appraisal of which country/continent has
the deadliest snakes.
Anyone perusing the literature will have seen reference to the LD50 using
mice to measure relative toxicities of various snake venoms. This is great data
if you are a veterinarian specialising in the treatment of snake-bitten mice! I
believe it has little relevance when gauging the danger of a particular species
to humans. The LD50 is scientifically indefensible in this regard. The snake
currently ranking number one on that list has not been the cause of death to a
human in any documented case history that I have seen. No doubt, Australia's
medical scientists can take some credit for this. However, the Russell's Viper (Daboia
russelli) found from Pakistan to China and Indonesia; the "lance-headed" group
of pit-vipers (Bothrops spp.) of South America, the "saw-scaled" vipers (Echis
spp.) of northern Africa, the Middle East, India and Sri Lanka are believed
responsible for up to 50,000 deaths each year (Swaroop & Grab, 1954) and do not
rank a mention. Maybe there has been no comparison made yet, or maybe they have
venoms that are more dangerous to humans than to mice.
Number 24 on that list (Broad et al., 1979) is the Olive Whip Snake (Demansia
olivacea). I believe it would have Buckley's chance of killing any human except
maybe a decrepit old snake handler hypersensitive after years of continual
exposure to venoms. All the LD50 does is compare the different venoms'
toxicities on mice and is, therefore, biased towards mammal-specific feeders. To
be more relevant each specific venom must have the LD50 criterion applied using
a variety of animals such as fish, frogs and birds. Even then, the data
collected would not reflect the toxicities of the respective venoms on humans.
Mouse tissue is 50 times less responsive to Sydney Funnelweb Spider (Atrax
robustus) venom than tissue from humans or monkeys (Underhill, 1988: 170).
Kellaway (1934: 678) found that adult mice were unaffected by A. robustus venom.
A worker could mistakenly judge this spider to be harmless when examining the
LD50 toxicity of its venom on mice!
Remember also that Australia's snakes rarely envenom when biting defensively.
Envenomation occurs in less than 1 in 10 bites (Sutherland & King, 1991: 1), or
is it that a minority of people bitten experience systematic envenomation due to
a hypersensitive reaction to the venom?
Many of Australia's venomous snakes such as Pseudonaja spp. do not even wait
for their venom to immobilise prey. Instead, using constriction to restrain it,
they often swallow it alive. I am of the opinion its primary purpose is
digestion.
I can't help wondering, why has there been this preoccupation with the
emphasis on exaggerating the danger of Australia's venomous snakes? Could it be
that many of the researchers involved are government funded. They would have a
vested interest in obtaining results that would most suit a favourable decision
on continued funding.
It is probable that more people die each year in Australia from horse riding
related accidents than snakebite. We do not go around hitting horses on the head
with a shovel!
Those educators specialising in reptiles must definitely do all in their
power to improve the snake's image. Rather than promote the negatives, emphasise
the positives!
Figure 2 is from Sutherland (1992 & 1994), media reports and other sources to
1998. It presents the causes of snakebite believed to have resulted in 30 deaths
in the past 18 years in Australia. An increased awareness of snakes through
education and appropriate footwear could have reduced this by 16. A further
reduction of 13.3% may have been possible if it was illegal to kill snakes. Four
of the above victims may have still been alive today. The fact is that while the
relevant wildlife authorities allow the killing of snakes they are directly
contributing to the frequency of snakebite and therefore fatalities from this.
Both professional and amateur herpetologists must encourage a more positive
attitude towards Australian snakes. This means less emphasis on the irrelevant
laboratory tests of venom toxicity.
Those in a position of authority perpetuate many myths unknowingly. For
example, some diving instructors continue to incorrectly refer to the "small
mouth and rear fangs" in sea snakes. They often comment that sea snakes can only
bite between the fingers or on the ear lobes. This is far from the truth (see
Limpus, 1987 Pg 198). Zimmerman (1988) relates an experience where a Stokes Sea
Snake (Astrotia stokesii) bites both a camera's strobe arm and a diving flipper
thrust towards it. However, there are no documented fatalities in Australia from
sea snake bite.
I once had an article refereed and returned with the comment that "......
Australia's elapids have grooved fangs". Along most of the fang's length this "groove"
is a closed seam, only being opened towards the tip where it does not detract
significantly from the fang's function or effectiveness.
Many people make an erroneous distinction between tiger snakes' (Notechis spp.)
fangs and Taipans' (Oxyuranus scutellatus), saying the former differ by being
grooved. The only distinction is the length, in both species they are
effectively hollow.
On another occasion and another referee a problem with semantics arose in
reference to the words "dangerously venomous". The comment came back. "...delete
dangerously, you already have venomous". These terms are far from synonymous!
We strive for objectivity but when dealing with snakes, subjectivity commonly
comes to the fore. Many believe the widespread fear of these animals is a result
of teaching but, after working with aborigines, I think that in many of us our
fear is instinctive. On top of this we have the added burden of the way snakes
have been portrayed historically. Moses, in the Book of Genesis, symbolised evil
as a serpent. As snakes were the bad guys already he wasn't treading on any toes.
The mythical Medusa and Cleopatra do little to improve the image.
To increase people's awareness and improve the snake's image in Australia
much more positive information must be available in any educational session.
Maybe this will encourage people's want to conserve them.
I am of the opinion that changes to the relevant Policies and Acts allowing
the killing of snakes need to occur to place more responsibility on the person
to justify the killing. The respective wildlife authorities have only limited
resources for the education needed to bring about this type of change. However,
both amateur and professional herps, with our altruism are ready to go. Tread
carefully though, do not fall into the trap of perpetuating the myth just
because someone else did.
Ponder On This
One of a government's responsibilities is to protect its people. In allowing
the killing of venomous snakes it contributes towards snakebite resulting in
injury and death. Therefore it may be negligent in its responsibility by
continuing to endorse open seasons or similar.
The LD50 Described
The LD50 is a standard laboratory test with set guidelines laid down by the
World Health Organisation. With the toxicity test in snakes, individual mice
within a sample receive equivalent quantities of venom (each mouse is of the
same weight). Each sample receives less venom than the previous. The LD50 is the
amount of venom administered to each mouse to cause 50% of the sample to die.
The lower the LD50 the higher the toxicity is on mice!. For the limitations and
problems with this type of test see White (1987).
The Answers To Some Common Questions
Australia's most venomous (yield) snake is the King Brown (Pseudechis
australis). Believed involved in very few fatalities.
The most toxic snake venom on mice (of the species tested) is the Inland
Taipan (Oxyuranus microlepidotus). See Figure 3.
Australia's deadliest snakes are the brownsnakes (Pseudonaja spp.). Believed
involved in 18 of the past 28 deaths attributed to snakebite. See Figure 4.
The world's deadliest snake, based on documented deaths, is probably the
Saw-scaled Viper (Echis carinatus) especially in Sri Lanka. The deaths of nearly
fifty people per million from snakebite occur there each year. Today in
Australia we have 0.13/million deaths each year. See Figure 1.
The most misrepresented data by the Australian herpetological community is
the list of snakes showing their lethality on mice compiled by Broad et al
(1979). Often presented as if it directly relates to humans. It does not.
Acknowledgment
I thank Pat Garland for his critical appraisal and constructive comments on
this article, much of which comes from the heart not the head.
References
BROAD, A.J., SUTHERLAND, S.K. & COULTER, A.R 1979. The lethality in mice of
dangerous Australian and other snake venom. Toxicon 17: 661-664.
KELLAWAY, C.H. 1934. A note on the venom of the Sydney Funnelweb Spider Atrax
robustus Med. J. Aust.. 1: 678-9.
LIMPUS, C. 1987. Sea Snakes. Pp 195-204 In Toxic Plants & Animals, a Guide for
Australia.. (Eds. J. Covacevich, P. Davie & J. Pearn) Queensland Museum.
MUNRO, D. 1988. Chambers World Gazetteer. 5th Edit. Chambers & Cambridge,
International.
PARRISH, H.M. 1963. Analysis of 460 fatalities from venomous animals in the
United States. Amer. J. Med. Sc. (Feb).
SPAWLS, S. & BRANCH, B. 1995. The Dangerous Snakes of Africa.
SUTHERLAND, S.K. 1992. Deaths from snake bite in Australia 1981-1991. Med. J.
Aust. Vol. 157: 740-746.
SUTHERLAND, S.K. 1995. Snakebite deaths in Australia 1992-1994 and a management
update. Med. J. Aust. Vol. 163: 616-618.
SUTHERLAND, S.K. & KING, K. 1991. Management of snake-bite injuries. RFDSA
Monograph Series 1: 1-12.
SWAROOP, S. & GRAB, B. 1954. Snake bite mortality in the world. Bull. of World
Health Organisation 10: 35-76.
TRINCA, J.C. 1963. The treatment of snake bite. Med. J. Aust. 1: 275-280.
UNDERHILL, D. 1988. Australia's Dangerous Creatures. Readers Digest, Sydney.
368pp.
WHITE, J. 1987. Elapid Snakes: Venom Toxicities and Actions. Pp 369-89In Toxic
Plants & Animals, a Guide for Australia. (Eds. J. Covacevich, P. Davie & J.
Pearn) Queensland Museum.
ZIMMERMAN, K.D. 1988. The question of sea snake aggression. Herpetofauna 18(2):
11.
Figure 1. A comparison of annual snakebite fatalities per million people from
around the world. To standardise comparisons published data compiled between
1945-1960 used. Australia's current figure is 0.13 per million however for
relevant period used here it was 0.45 per million.
Venom toxicity is only one of many contributing factors determining how
dangerous a particular species is. Australia's snakes pale to almost
insignificance when compared to the fatalities caused by their counterparts in
other parts of the world. The above figures are very conservative for the
developing countries sampled, eg, West Africa has recently been found to have
23,000 deaths each year with less than 10% of victims being treated in modern
medical facilities (Spawls & Branch, 1995). Many victims probably die in the
bush and are not included in any sample. The 23,000 figure may be very
conservative!
Data for USA from Parrish (1963); Africa, India and South America from
Swaroop & Grab (1954); and Australia from Trinca (1963). Populations are from
Munro (1988).
Figure 2. Comparing the relative frequency of causes of snakebite in
Australia resulting in the deaths of 30 people over a 18 year period (from
Sutherland, 1992 & 1994 and media reports for 1993-98).
Accident - unavoidable without exceptional awareness.
Herp - herpetologist bitten while handling snake.
Kill - bitten while killing snake.
Mis ID - bitten while handling venomous snake believing it to be harmless.
Trod - bitten after treading on snake.
? - insufficient data to determine cause.
LETHALITY IN MICE
From Broad, Sutherland & Coulter (1979)
(In descending order including LD50 in mg/kg. In first figure venom diluted
in saline solution only, 2nd includes the addition of a blood protein, bovine
serum albumin)
Inland Taipan (Oxyuranus microlepidotus) 0.025 0.010
Eastern Brown Snake (Pseudonaja textilis) 0.053 0.041
Northern Taipan (Oxyuranus scutellatus) 0.099 0.064
Eastern Mainland Tiger Snake (Notechis s. scutatus) 0.118 0.118
Reevesby Island Tiger Snake (Notechis ater niger) 0.131 0.099
Beaked Sea Snake (Enhydrina schistosa) 0.164 0.173
Western Mainland Tiger Snake (Notechis scutatus occidentalis) 0.194 0.124
Chappell Island Tiger Snake (Notechis ater serventyi) 0.338 0.271
Southern Death Adder (Acanthophis antarcticus) 0.400 0.338
Copperhead (Austrelaps superbus) 0.560 0.500
Indian Cobra (Naja naja) 0.565 0.500
Black Mamba (Dendroaspis polylepis)
Dugite (Pseudonaja a. affinis) 0.660 0.560
Papuan Black Snake (Pseudechis papuanus) 1.09 1.36
Stephens's Banded Snake (Hoplocephalus stephensii) 1.36 1.44
Rough-scaled Snake (Tropidechis carinatus) 1.36 1.09
King Cobra (Ophiophagus hannah) 1.80 1.91
Spotted Black Snake (Pseudechis guttatus) 2.13 1.53
Collett's Snake (Pseudechis colletti) 2.38
King Brown Snake (Pseudechis australis) 2.38 1.91
Red-bellied Black Snake (Pseudechis porphyriacus) 2.52 2.53
Small-eyed Snake (Cryptophis nigrescens) 2.67
Olive Whip Snake (Demansia olivacea)
Eastern Diamond-backed Rattlesnake (Crotalus adamanteus) 11.4 7.70
Figure 3. The most widely misrepresented data concerning venomous snakes in
Australia. It is usually stated that this ranking is an undisputable reflection
of dangerousness.
Figure 4. Comparative frequency of fatalities relative to the five species of
snake believed involved for the 18 year period 1980-1998.
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