The
Komodo dragon[4] (
Varanus komodoensis), also known as the
Komodo monitor, is a large species of
lizard found in the
Indonesian islands of
Komodo,
Rinca,
Flores,
Gili Motang, and Padar.
[5] A member of the
monitor lizard family
Varanidae,
it is the largest living species of lizard, growing to a maximum length
of 3 metres (10 ft) in rare cases and weighing up to approximately 70
kilograms (150 lb).
[5]
Their unusually large size has been attributed to
island gigantism, since no other carnivorous animals fill the
niche on the islands where they live.
[6][7] However, recent research suggests the large size of Komodo dragons may be better understood as representative of a
relict population of very large
varanid lizards that once lived across Indonesia and Australia, most of which, along with other
megafauna,
[1] died out after the
Pleistocene. Fossils very similar to
V. komodoensis have been found in Australia dating to greater than 3.8 million years ago, and its body size remained stable on
Flores,
one of the handful of Indonesian islands where it is currently found,
over the last 900,000 years, "a time marked by major faunal turnovers,
extinction of the island's megafauna, and the arrival of early hominids
by 880 ka [kiloannums]."
[1]
As a result of their size, these lizards dominate the
ecosystems in which they live.
[8] Komodo dragons hunt and ambush prey including
invertebrates,
birds, and
mammals.
It has been claimed that they have a venomous bite; there are two
glands in the lower jaw which secrete several toxic proteins. The
biological significance of these proteins is disputed, but the glands
have been shown to secrete an
anticoagulant.
Komodo dragon group behaviour in hunting is exceptional in the reptile
world. The diet of big Komodo dragons mainly consists of deer, though
they also eat considerable amounts of
carrion.
[5] Komodo dragons also occasionally attack humans in the area of
West Manggarai Regency where they live in Indonesia.
[9]
Mating begins between May and August, and the eggs are laid in September. About 20 eggs are deposited in abandoned
megapode nests or in a self-dug nesting hole.
[5]
The eggs are incubated for seven to eight months, hatching in April,
when insects are most plentiful. Young Komodo dragons are vulnerable and
therefore dwell in trees, safe from predators and
cannibalistic adults. They take 8 to 9 years to mature, and are estimated to live up to 30 years.
[5]
Komodo dragons were first recorded by Western scientists in 1910.
[10]
Their large size and fearsome reputation make them popular zoo
exhibits. In the wild, their range has contracted due to human
activities, and they are listed as
vulnerable by the
IUCN.
[2] They are protected under Indonesian law, and a
national park,
Komodo National Park, was founded to aid protection efforts.
Etymology
The Komodo dragon is also known as the Komodo monitor or the Komodo Island monitor in scientific literature,
[4] although this is not very common. To the natives of
Komodo Island, it is referred to as
ora,
buaya darat (land crocodile), or
biawak raksasa (giant monitor).
[11][12]
Evolutionary history
The evolutionary development of the Komodo dragon started with the
Varanus genus, which originated in
Asia about 40 million years ago and migrated to
Australia.
Around 15 million years ago, a collision between Australia and
Southeast Asia allowed the varanids to move into what is now the
Indonesian archipelago, extending their range as far east as the island
of
Timor.
The Komodo dragon was believed to have differentiated from its
Australian ancestors 4 million years ago. However, recent fossil
evidence from
Queensland suggests the Komodo dragon evolved in Australia before spreading to Indonesia.
[1][13] Dramatic lowering of sea level during the
last glacial period
uncovered extensive stretches of continental shelf that the Komodo
dragon colonised, becoming isolated in their present island range as sea
levels rose afterwards.
[1][12]
Description
Closeup of the head and fore-quarters
In the wild, an adult Komodo dragon usually weighs around 70 kg (150 lb), although captive specimens often weigh more.
[14] According to the
Guinness Book of World Records,
an average adult male will weigh 79 to 91 kg (174 to 201 lb) and
measure 2.59 m (8.5 ft), while an average female will weigh 68 to 73 kg
(150 to 161 lb) and measure 2.29 m (7.5 ft).
[15] The largest verified wild specimen was 3.13 m (10.3 ft) long and weighed 166 kg (366 lb), including undigested food.
[12]
The Komodo dragon has a tail as long as its body, as well as about 60
frequently replaced, serrated teeth that can measure up to 2.5 cm (1 in)
in length. Its saliva is frequently blood-tinged, because its teeth are
almost completely covered by
gingival tissue that is naturally lacerated during feeding.
[16] It also has a long, yellow, deeply forked tongue.
[12] Komodo dragon skin is reinforced by armoured scales, which contain tiny bones called
osteoderms that function as a sort of natural chain-mail.
[17][18] This rugged hide makes Komodo dragon skin poorly suited for making into
leather.
Senses
As with other varanids, Komodo dragons have only a single ear bone, the
stapes, for transferring vibrations from the
tympanic membrane to the
cochlea. This arrangement means they are likely restricted to sounds in the 400 to 2,000
hertz range, compared to humans who hear between 20 and 20,000 hertz.
[12][19] It was formerly thought to be
deaf
when a study reported no agitation in wild Komodo dragons in response
to whispers, raised voices, or shouts. This was disputed when
London Zoological Garden
employee Joan Proctor trained a captive specimen to come out to feed at
the sound of her voice, even when she could not be seen.
[20]
The Komodo dragon can see objects as far away as 300 m (980 ft), but because its retinas only contain
cones,
it is thought to have poor night vision. The Komodo dragon is able to
see in colour, but has poor visual discrimination of stationary objects.
[21]
Komodo dragon using their tongue to sample the air
The Komodo dragon uses its tongue to detect,
taste, and
smell stimuli, as with many other reptiles, with the
vomeronasal sense using the
Jacobson's organ, rather than using the nostrils.
[22]
With the help of a favorable wind and its habit of swinging its head
from side to side as it walks, a Komodo dragon may be able to detect
carrion from 4–9.5 km (2.5–5.9 mi) away.
[21] It only has a few
taste buds in the back of its throat.
[22] Its scales, some of which are reinforced with bone, have
sensory plaques
connected to nerves to facilitate its sense of touch. The scales around
the ears, lips, chin, and soles of the feet may have three or more
sensory plaques.
[16]
Behaviour and ecology
The Komodo dragon prefers hot and dry places, and typically lives in
dry, open grassland, savanna, and tropical forest at low elevations. As
an
ectotherm, it is most active in the day, although it exhibits some
nocturnal
activity. Komodo dragons are solitary, coming together only to breed
and eat. They are capable of running rapidly in brief sprints up to
20 km/h (12 mph), diving up to 4.5 m (15 ft), and climbing trees
proficiently when young through use of their strong claws.
[14] To catch out-of-reach prey, the Komodo dragon may stand on its hind legs and use its tail as a support.
[20] As it matures, its claws are used primarily as weapons, as its great size makes climbing impractical.
[16]
For shelter, the Komodo dragon digs holes that can measure from 1 to
3 m (3.3 to 9.8 ft) wide with its powerful forelimbs and claws.
[23]
Because of its large size and habit of sleeping in these burrows, it is
able to conserve body heat throughout the night and minimise its
basking period the morning after.
[24] The Komodo dragon hunts in the afternoon, but stays in the shade during the hottest part of the day.
[25]
These special resting places, usually located on ridges with cool sea
breezes, are marked with droppings and are cleared of vegetation. They
serve as strategic locations from which to ambush deer.
[26]
Diet
Komodo dragons are carnivores. Although they eat mostly carrion,
[6]
they will also ambush live prey with a stealthy approach. When suitable
prey arrives near a dragon's ambush site, it will suddenly charge at
the animal and go for the underside or the throat.
[16]
It is able to locate its prey using its keen sense of smell, which can
locate a dead or dying animal from a range of up to 9.5 km (5.9 mi).
Komodo dragons have been observed knocking down large pigs and deer with
their strong tails.
[27][28]
Komodo dragons eat by tearing large chunks of flesh and swallowing
them whole while holding the carcass down with their forelegs. For
smaller prey up to the size of a goat, their loosely articulated jaws,
flexible skulls, and expandable stomachs allow them to swallow prey
whole. The vegetable contents of the stomach and intestines are
typically avoided.
[26]
Copious amounts of red saliva the Komodo dragons produce help to
lubricate the food, but swallowing is still a long process
(15–20 minutes to swallow a goat). A Komodo dragon may attempt to speed
up the process by ramming the carcass against a tree to force it down
its throat, sometimes ramming so forcefully, the tree is knocked down.
[26] A small tube under the tongue that connects to the lungs allows it to breathe while swallowing.
[16] After eating up to 80% of its body weight in one meal,
[8]
it drags itself to a sunny location to speed digestion, as the food
could rot and poison the dragon if left undigested for too long. Because
of their slow metabolism, large dragons can survive on as few as 12
meals a year.
[16]
After digestion, the Komodo dragon regurgitates a mass of horns, hair,
and teeth known as the gastric pellet, which is covered in malodorous
mucus. After regurgitating the gastric pellet, it rubs its face in the
dirt or on bushes to get rid of the mucus, suggesting it does not relish
the scent of its own excretions.
[16]
Young Komodo dragon feeding on a water buffalo carcass
The largest animals eat first, while the smaller ones follow a
hierarchy. The largest male asserts his dominance and the smaller males
show their submission by use of body language and rumbling hisses.
Dragons of equal size may resort to "wrestling". Losers usually retreat,
though they have been known to be killed and eaten by victors.
[29]
Komodo excrement has a dark portion, which is stool, and a whitish portion which is
urate, the nitrogenous end-product of their digestion process.
[30]
The Komodo dragon's diet is wide-ranging, and includes
invertebrates, other reptiles (including smaller Komodo dragons),
birds, bird eggs, small mammals, monkeys, wild boar, goats, deer, horses, and water buffalo.
[31] Young Komodos will eat insects, eggs,
geckos, and small mammals.
[6] Occasionally, they attack and bite
humans (see first paragraphs of this article). Sometimes they consume human corpses, digging up bodies from shallow graves.
[20]
This habit of raiding graves caused the villagers of Komodo to move
their graves from sandy to clay ground and pile rocks on top of them to
deter the lizards.
[26] The Komodo dragon may have evolved to feed on the extinct
dwarf elephant Stegodon that once lived on Flores, according to evolutionary biologist
Jared Diamond.
[32]
The Komodo dragon drinks by sucking water into its mouth via
buccal pumping (a process also used for respiration), lifting its head, and letting the water run down its throat.
[28]
Saliva
Although previous studies proposed that Komodo dragon saliva contains
a variety of highly septic bacteria that would help to bring down prey,
[29][33]
research in 2013 suggested that the bacteria in the mouths of Komodo
dragons are ordinary and similar to those found in other carnivores.
They actually have surprisingly good mouth hygiene. As Bryan Fry put it:
"After they are done feeding, they will spend 10 to 15 minutes
lip-licking and rubbing their head in the leaves to clean their mouth...
Unlike people have been led to believe, they do not have chunks of
rotting flesh from their meals on their teeth, cultivating bacteria."
The observation of prey dying of sepsis would then be explained by the
natural instinct of
water buffalos,
who are not native to the islands where the Komodo dragon lives, to run
into water when attacked. The warm, faeces-filled water would then
cause the infections.
[34] The study used samples from 16 captive dragons (10 adults and six neonates) from three U.S. zoos.
[35]
Venom
In late 2005, researchers at the
University of Melbourne speculated the
perentie (
Varanus giganteus), other species of monitors, and
agamids
may be somewhat venomous. The team believes the immediate effects of
bites from these lizards were caused by mild envenomation. Bites on
human digits by a
lace monitor (
V. varius), a Komodo dragon, and a spotted tree monitor (
V. scalaris)
all produced similar effects: rapid swelling, localised disruption of
blood clotting, and shooting pain up to the elbow, with some symptoms
lasting for several hours.
[36]
In 2009, the same researchers published further evidence demonstrating Komodo dragons possess a venomous bite.
MRI scans of a preserved
skull showed the presence of two
glands in the lower jaw. The researchers extracted one of these glands from the head of a terminally ill dragon in the
Singapore Zoological Gardens, and found it secreted several different toxic
proteins.
The known functions of these proteins include inhibition of blood
clotting, lowering of blood pressure, muscle paralysis, and the
induction of hypothermia, leading to shock and loss of consciousness in
envenomated prey.
[37][38] As a result of the discovery, the previous theory that bacteria were responsible for the deaths of Komodo victims was disputed.
[39]
Kurt Schwenk, an
evolutionary biologist at the
University of Connecticut,
finds the discovery of these glands intriguing, but considers most of
the evidence for venom in the study to be "meaningless, irrelevant,
incorrect or falsely misleading". Even if the lizards have venom-like
proteins in their mouths, Schwenk argues, they may be using them for a
different function, and he doubts venom is necessary to explain the
effect of a Komodo dragon bite, arguing that shock and blood loss are
the primary factors.
[40][41]
Other scientists have stated that this allegation of venom glands
"has had the effect of underestimating the variety of complex roles
played by oral secretions in the biology of reptiles, produced a very
narrow view of oral secretions and resulted in misinterpretation of
reptilian evolution". According to these scientists "reptilian oral
secretions contribute to many biological roles other than to quickly
dispatch prey". These researchers concluded that, "Calling all in this
clade venomous implies an overall potential danger that does not exist,
misleads in the assessment of medical risks, and confuses the biological
assessment of squamate biochemical systems".
[42]
Reproduction
Mating occurs between May and August, with the eggs laid in September.
[12]
During this period, males fight over females and territory by grappling
with one another upon their hind legs, with the loser eventually being
pinned to the ground. These males may vomit or defecate when preparing
for the fight.
[20] The winner of the fight will then flick his long tongue at the female to gain information about her receptivity.
[8] Females are
antagonistic
and resist with their claws and teeth during the early phases of
courtship. Therefore, the male must fully restrain the female during
coitus to avoid being hurt. Other courtship displays include males
rubbing their chins on the female, hard scratches to the back, and
licking.
[43] Copulation occurs when the male inserts one of his
hemipenes into the female's
cloaca.
[21] Komodo dragons may be monogamous and form "pair bonds", a rare behavior for lizards.
[20]
Komodo dragon with its long
tail and
claws fully visible
Female
Komodos lay their eggs from August to September and may use several
types of locality; in one study, 60% laid their eggs in the nests of
orange-footed scrubfowl (a moundbuilder or
megapode), 20% on ground level and 20% in hilly areas.
[44] The females make many camouflage nests/holes to prevent other dragons from eating the eggs.
[45] Clutches contain an average of 20 eggs, which have an incubation period of 7–8 months.
[20] Hatching is an exhausting effort for the neonates, which break out of their eggshells with an
egg tooth
that falls off soon after. After cutting themselves out, the hatchlings
may lie in their eggshells for hours before starting to dig out of the
nest. They are born quite defenseless and are vulnerable to predation.
[29] Sixteen youngsters from a single nest were on average 46.5 cm long and weighed 105.1 grams.
[44]
Young Komodo dragons spend much of their first few years in trees,
where they are relatively safe from predators, including cannibalistic
adults, as juvenile dragons make up 10% of their diets.
[20]
The habit of cannibalism may be advantageous in sustaining the large
size of adults, as medium-sized prey on the islands is rare.
[27]
When the young approach a kill, they roll around in faecal matter and
rest in the intestines of eviscerated animals to deter these hungry
adults.
[20] Komodo dragons take approximately 8 to 9 years to mature, and may live for up to 30 years.
[5]
Parthenogenesis
A Komodo dragon at London Zoo named Sungai laid a clutch of eggs in
late 2005 after being separated from male company for more than two
years. Scientists initially assumed she had been able to store
sperm from her earlier encounter with a male, an
adaptation known as
superfecundation.
[46] On 20 December 2006, it was reported that Flora, a captive Komodo dragon living in the
Chester Zoo in
England,
was the second known Komodo dragon to have laid unfertilised eggs: she
laid 11 eggs, and seven of them hatched, all of them male.
[47] Scientists at
Liverpool University
in England performed genetic tests on three eggs that collapsed after
being moved to an incubator, and verified Flora had never been in
physical contact with a male dragon. After Flora's eggs' condition had
been discovered, testing showed Sungai's eggs were also produced without
outside fertilization.
[48] On 31 January 2008, the
Sedgwick County Zoo in
Wichita, Kansas, became the first zoo in the Americas to document
parthenogenesis
in Komodo dragons. The zoo has two adult female Komodo dragons, one of
which laid about 17 eggs on 19–20 May 2007. Only two eggs were incubated
and hatched due to space issues; the first hatched on 31 January 2008,
while the second hatched on 1 February. Both hatchlings were males.
[49][50]
Komodo dragons have the
ZW chromosomal
sex-determination system, as opposed to the
mammalian XY system. Male progeny prove Flora's unfertilised eggs were
haploid (n) and doubled their chromosomes later to become
diploid (2n) (by being fertilised by a
polar body, or by chromosome duplication without
cell division), rather than by her laying diploid eggs by one of the
meiosis reduction-divisions in her
ovaries
failing. When a female Komodo dragon (with ZW sex chromosomes)
reproduces in this manner, she provides her progeny with only one
chromosome from each of her pairs of chromosomes, including only one of
her two sex chromosomes. This single set of chromosomes is duplicated in
the egg, which develops parthenogenetically. Eggs receiving a Z
chromosome become ZZ (male); those receiving a W chromosome become WW and fail to develop,
[51][52] meaning that only males are produced by parthenogenesis in this species.
It has been hypothesised that this reproductive adaptation allows a single female to enter an isolated
ecological niche (such as an island) and by
parthenogenesis
produce male offspring, thereby establishing a sexually reproducing
population (via reproduction with her offspring that can result in both
male and female young).
[51] Despite the advantages of such an adaptation, zoos are cautioned that parthenogenesis may be detrimental to genetic diversity.
[53]
History
Discovery by the Western world
Komodo dragon coin, issued by Indonesia
Komodo dragons were first documented by
Europeans in 1910, when rumors of a "land crocodile" reached Lieutenant van Steyn van Hensbroek of the Dutch colonial administration.
[54] Widespread notoriety came after 1912, when Peter Ouwens, the director of the Zoological Museum at
Bogor,
Java,
published a paper on the topic after receiving a photo and a skin from
the lieutenant, as well as two other specimens from a collector.
[3] The first two live Komodo dragons to arrive in Europe were exhibited in the Reptile House at London Zoo when it opened in 1927.
[55] Joan Beauchamp Procter
made some of the earliest observations of these animals in captivity
and she demonstrated the behaviour of one of these animals at a
Scientific Meeting of the
Zoological Society of London in 1928.
[56] The Komodo dragon was the driving factor for an expedition to
Komodo Island
by W. Douglas Burden in 1926. After returning with 12 preserved
specimens and 2 live ones, this expedition provided the inspiration for
the 1933 movie
King Kong.
[57] It was also Burden who coined the common name "Komodo dragon."
[25] Three of his specimens were stuffed and are still on display in the
American Museum of Natural History.
[58]
Studies
The Dutch, realizing the limited number of individuals in the wild,
outlawed sport hunting and heavily limited the number of individuals
taken for scientific study. Collecting expeditions ground to a halt with
the occurrence of World War II, not resuming until the 1950s and 1960s,
when studies examined the Komodo dragon's feeding behavior,
reproduction, and body temperature. At around this time, an expedition
was planned in which a long-term study of the Komodo dragon would be
undertaken. This task was given to the Auffenberg family, who stayed on
Komodo Island for 11 months in 1969. During their stay,
Walter Auffenberg and his assistant Putra Sastrawan captured and tagged more than 50 Komodo dragons.
[59] The research from the Auffenberg expedition would prove to be enormously influential in raising Komodo dragons in captivity.
[60]
Research after that of the Auffenberg family has shed more light on the
nature of the Komodo dragon, with biologists such as Claudio Ciofi
continuing to study the creatures.
[61]
Conservation
The Komodo dragon is a
vulnerable species and is on the
IUCN Red List.
[2] The
Komodo National Park was founded in 1980 to protect Komodo dragon populations on islands including Komodo, Rinca, and Padar.
[62] Later, the Wae Wuul and Wolo Tado Reserves were opened on Flores to aid with Komodo dragon conservation.
[61]
Komodo dragons avoid encounters with humans. Juveniles are very shy
and will flee quickly into a hideout if a human comes closer than about
100 metres (330 ft). Older animals will also retreat from humans from a
shorter distance away. If cornered, they will react aggressively by
gaping their mouth, hissing, and swinging their tail. If they are
disturbed further, they may start an attack and bite. Although there are
anecdotes of unprovoked Komodo dragons attacking or preying on humans,
most of these reports are either not reputable or caused by defensive
bites. Only a very few cases are truly the result of unprovoked attacks
by abnormal individuals, which lost their fear towards humans.
[29]
Volcanic activity, earthquakes, loss of habitat, fire,
[16][61]
loss of prey due to poaching, tourism, and illegal poaching of the
dragons themselves have all contributed to the vulnerable status of the
Komodo dragon. Under Appendix I of
CITES (the Convention on International Trade in Endangered Species), commercial trade of skins or specimens is illegal.
[63][64]
In 2013, total population in the wild was assessed as 3,222
individuals, declining to 3,092 in 2014 and 3,014 in 2015. Populations
remained relatively stable on the bigger islands (Komodo and Rinca), but
decreased on smaller island such as Nusa Kode and Gili Motang, likely
due to diminishing prey availability.
[65] On
Padar, a former population of the Komodo dragon became extinct, of which the last individuals were seen in 1975.
[66]
It is widely assumed that the Komodo dragon died out on Padar after a
strong decline of the populations of large ungulate prey, for which
poaching was most likely responsible.
[67]
In captivity
Profile showing the external earholes behind the eyes. Komodo dragons hear a smaller range of frequencies compared to humans.
Komodo dragon with keeper
Komodo dragons have long been great zoo attractions, where their size
and reputation make them popular exhibits. They are, however, rare in
zoos because they are susceptible to infection and parasitic disease if
captured from the wild, and do not readily reproduce.
[11]
As of May 2009, there were 13 European, 2 African, 35 North American, 1
Singaporean, and 2 Australian institutions that kept Komodo dragons.
[68]
The first Komodo dragons were displayed at
London Zoo in 1927. A Komodo dragon was exhibited in 1934 at the
National Zoo in Washington, D.C.,
but it lived for only two years. More attempts to exhibit Komodo
dragons were made, but the lifespan of these animals was very short,
averaging five years in the National Zoological Park. Studies done by
Walter Auffenberg, which were documented in his book
The Behavioral Ecology of the Komodo Monitor, eventually allowed for more successful managing and reproducing of the dragons in captivity.
[60]
A variety of behaviors have been observed from captive specimens. Most individuals are relatively tame within a short time,
[69][70] and are capable of recognising individual humans and discriminating between familiar keepers.
[71]
Komodo dragons have also been observed to engage in play with a variety
of objects, including shovels, cans, plastic rings, and shoes. This
behavior does not seem to be "food-motivated predatory behavior".
[8][12][72]
Even seemingly docile dragons may become unpredictably aggressive,
especially when the animal's territory is invaded by someone unfamiliar.
In June 2001, a Komodo dragon seriously injured
Phil Bronstein, the then husband of actress
Sharon Stone, when he entered its enclosure at the
Los Angeles Zoo
after being invited in by its keeper. Bronstein was bitten on his bare
foot, as the keeper had told him to take off his white shoes and socks,
which the keeper stated could potentially excite the Komodo dragon as
they were the same colour as the white rats the zoo fed the dragon.
[73][74] Although he escaped, Bronstein needed to have several tendons in his foot reattached surgically.
[75]
See also
