''Varanus scalaris'' is a small
species
A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
monitor lizard
Monitor lizards are lizards in the genus ''Varanus,'' the only extant genus in the family Varanidae. They are native to Africa, Asia, and Oceania, and West African Nile monitor, one species is also found in south America as an invasive species. A ...
. It is often referred to as the banded tree monitor or the spotted tree monitor.
It is found in
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
in the states of
Western Australia
Western Australia (WA) is the westernmost state of Australia. It is bounded by the Indian Ocean to the north and west, the Southern Ocean to the south, the Northern Territory to the north-east, and South Australia to the south-east. Western Aust ...
and
Queensland
Queensland ( , commonly abbreviated as Qld) is a States and territories of Australia, state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Austr ...
as well as the
Northern Territory
The Northern Territory (abbreviated as NT; known formally as the Northern Territory of Australia and informally as the Territory) is an states and territories of Australia, Australian internal territory in the central and central-northern regi ...
, the province of
Papua,
Indonesia
Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...
and in
Papua New Guinea
Papua New Guinea, officially the Independent State of Papua New Guinea, is an island country in Oceania that comprises the eastern half of the island of New Guinea and offshore islands in Melanesia, a region of the southwestern Pacific Ocean n ...
.
The species inhabits trees in the
savanna
A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
woodlands and forages for food in both trees and on the ground, with a diet consisting of insects as well as small vertebrates.
Venom
Like all other monitor lizards, banded tree monitors possess venom glands in their lower jaws, giving them a noticeably venomous bite.
The venom is an
anticoagulant
An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which ...
, and has two known mechanisms for disrupting blood clotting: by
fibrinogenolysis (the destructive cleavage of
fibrinogen
Fibrinogen (coagulation factor I) is a glycoprotein protein complex, complex, produced in the liver, that circulates in the blood of all vertebrates. During tissue and vascular injury, it is converted Enzyme, enzymatically by thrombin to fibrin ...
) and by blocking
platelet
Platelets or thrombocytes () are a part of blood whose function (along with the coagulation#Coagulation factors, coagulation factors) is to react to bleeding from blood vessel injury by clumping to form a thrombus, blood clot. Platelets have no ...
aggregation. The venom also causes
hypotension
Hypotension, also known as low blood pressure, is a cardiovascular condition characterized by abnormally reduced blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood and is ...
. Monitor lizard venom is extremely complex and diverse due to the great range of
ecological niches
In ecology, a niche is the match of a species to a specific environmental condition.
Three variants of ecological niche are described by
It describes how an organism or population responds to the distribution of resources and competitors (for e ...
that they occupy.
Banded tree monitors have the most potently fibrinogenolytic venoms of all monitor lizards, matched only by the similarly named tree monitors from the subgenus ''
Hapturosaurus''. This may be because arboreal monitor species experience strong
selection pressure
Evolutionary pressure, selective pressure or selection pressure is exerted by factors that reduce or increase reproductive success in a portion of a population, driving natural selection. It is a quantitative description of the amount of change oc ...
to quickly subjugate prey items before they break free and escape by falling out of the trees or flying away. As fibrinogenolytic activity is not painful, the venom likely has a primarily predatory role in subjugating prey, instead of acting as a predator deterrent.
It is suggested that higher prey escape potential may cause increased venom potency, as the lethally toxic
eastern green mamba and
boomslang
The boomslang ( or ; ''Dispholidus typus'') is a highly venomous snake in the family Colubridae. The species is native to Sub-Saharan Africa.
Etymology
Its common name means "tree snake" in Dutch and Afrikaans – ''boom'' meaning "tree", and ...
are also arboreal. This may also apply to the
piscivorous
A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...
and highly venomous
cone snails, given their highly mobile fish prey.
As the venom is an anticoagulant, monitor lizard bites often bleed far more than what the mechanical damage of the bite alone would have induced.
References
{{Taxonbar, from=Q3554681
Varanus
Lizards of Asia
Monitor lizards of Australia
Reptiles of Papua New Guinea
Reptiles of Indonesia
Reptiles of Queensland
Reptiles of Western Australia
Reptiles of the Northern Territory
Reptiles described in 1941
Taxa named by Robert Mertens