Animal Information

The Argus Monitor (Varanus panoptes) aka Yellow-Spotted Monitor

One of northern Australia’s largest predators, this species was formerly common, but has been decimated by Cane Toads. This carnivorous reptile lives in the tropical to semi-arid woodlands, particularly around floodplains and waterways. The same habitat cane toads use. The Argus monitor is listed as a vulnerable species.

The Argus monitor (Varanus panoptes), vah-RAH-nuss pan-OP-teez, commonly known as the yellow-spotted monitor. is native to the northern regions of Australia and southern New Guinea. In Australia, this reptile is typically called goanna. 

Varanus: a Latinisation of the Arabic word, Waran, for lizards of the Arabian Peninsula. These lizards were said to warn of the presence of crocodiles and became known in English as monitors.

While, panoptes means ‘all-seeing-eye’, referring to the spots that resemble eyes located all over the body.

The Argus Monitor is one of the largest species of the Varanus family. The three subspecies are Varanus panoptes rubidus, native to Western Australia, (rubidus referring to its reddish coloration). Varanus panoptes panoptes, native to Arnhem Land, the Kimberley Peninsula, and the Cape York Peninsula. Lastly, Varanus panoptes horni, found in New Guinea. The color of this reptile often varies with place of origin.

Most Argus monitors are yellow in color, with a background of brown or dark tan.

The size of an Argus monitor differs greatly between the sexes, with the female reaching an average total length of three feet (90 cm), while the male reaches an average of 4–5 feet (120–140 cm).

This Reptile Can Live 12-20 Years!

That Is A Long Time!!

The Argus monitor is a versatile predator and inhabits a large variety of biomes and habitats. They are primarily terrestrial, meaning they spend a great deal of time on the ground.

This species is an avid digger and will dig large burrows or take over an already existing burrow, where they spend a sizable portion of their time.

The Argus monitor is riparian inhabits and as such, it can usually be found around a permanent source of water.

Despite this, these lizards climb and will eagerly forage in trees. They are great swimmers and will even hunt in the water. These large lizards are quite fast and will run up to 100 yards/meters to the nearest tree or burrow when they are chased.

The Argus will raise up on their hind legs and support themselves with the tail. This unusual “tripod” behavior is used to spot potential prey or enemies from a distance when they feel threatened.

The Argus Monitor Is Venomous?

No Worries! All You Have To Do… Is Not Get Bitten!

Like most Varanus species, Argus monitors produce dangerous strains of bacteria that have been found to be actual venom. This venom is not fatal to humans but it may cause pain and illness.

The venom of Argus Monitor would be dangerous for small animals or infants. The venom prevents blood clotting and causes a rapid drop in blood pressure.

Argus Monitor Care

Argus Monitors Need Lots Of Space!

Argus monitors should be maintained between 85-90 degrees with a basking spot of 95 degrees. At night the temperature can drop to 75 degrees. This monitor species prefer long 12 hours of sunlight. Humidity should also be maintained at 60%-80%. 

UVB lighting is not a must for monitors but is recommended.  UVB lighting enables reptiles to metabolize calcium, by creating Vitamin D3.

However, because their diet consists of rodents and other live prey, they can usually receive enough D3 and calcium through their diet. The bones of the prey will provide calcium, while the liver will provide Vitamin D3.

Argus monitors prey on almost anything that it can overpower. This includes fish, crabs, small birds, rodents, insects and even other monitors.

The Argus monitor frequently preys on the dwarf monitors, Spiny-tailed goannas, and Kimberley rock monitors are eaten regularly.

Argus monitors have great senses, with smell being the most acute. Like all monitors, the Argus has a forked tongue and a vomeronasal organ in the roof of its mouth. It uses this organ in the same manner as snakes do and can often be seen flicking their tongues in search of a meal.

Listed on the IUCN Red List of Threatened Species, recent studies suggest that the cane toad infestation has severely damaged the population of Argus monitors. It is estimated that numbers have dropped by as much as 90% in many areas.

Breeding The Argus Monitor

Parthenogenesis is a type of asexual reproduction in which the offspring develops from unfertilized eggs. It is particularly common amongst arthropods and rotifers

Rare as it may be, this monitor is one of the few documented species to have parthenogenetic eggs hatch.

This is a genetic miscue versus adaptation, where the female provides two sets of chromosomes to the eggs, allowing them to develop and hatch.

Sexing of monitor lizards is difficult in neonates, but as they approach adulthood, this species shows certain traits that help deduce the sex of the animal.

Often, males develop very large and powerful front arms compared to females.

If viewed from the side, the base of the tail becomes very thick. When relaxed. the hemipenes can often be seen in a mature male.

The female will not display this thickness nor hemipenal bulges. Lastly, adult males get much larger than females. Males are often 4 1/2 feet long and quite massive versus their 2 1/2 feet long female counterparts.

When the female Argus is reproductive, she will suddenly become very fat in the abdomen. This sudden bloating is from vitellogenesis or yolking of the ova (eggs). The female also will often accept more food than normal at this time.

A couple of days after the bloating is witnessed, she will begin giving off chemical signals called pheromones. The male will be enticed by this. He will slowly and methodically follow her around the enclosure no matter where she goes.

The female will actually elicit the courtship by walking slowly and looking back at times. Eventually, the male will position himself on the back of the female, strum his hind leg on her tail and pelvis, and she will curl her tail up and allow mating to take place.

They will mate off and on, all day long, alternating sides/hemipenes session. This can last from two to seven days.

Following the mating sessions, the female will usually not tolerate any more copulations and (presumably) stops emitting the pheromones to mate as well.

The Argus monitor is Oviparous, meaning she lays eggs. It is important that the female needs to feed well and bask, as she feels necessary, during this critical time of egg development.

Keep an eye on the animals and decide what each individual needs. If the male is excessively dominant to feed and control the basking areas, a separation may be warranted.

Females lay 6 to 13 eggs between January and February.

Then It Takes Almost A Year To Hatch Them!

After approximately 27 to 30 days post-mating, the female will dig down into the cage substrate or nesting box and construct a nest. This is often done at night, and you can hear them meticulously digging for long hours.

Being careful not to rotate the eggs, transport the eggs into an egg box that is filled with approximately 1:1 by weight, not volume, water, and medium. Mediums include perlite (preferred by the author), vermiculite, HatchRite or sand.

Bury the eggs halfway in the medium, and place the box in an incubator set to 84 to 86 degrees. The eggs will incubate for 170 to 200 days. Vent the boxes weekly, or poke a few holes in the egg boxes for air exchange.

About a week prior to hatching, eggs will often dimple or dent. It is important to know that this denting is normal shedding of the water in the egg prior to hatching and not to add water mistakenly, assuming the eggs have become dry. 

Conservation Notes:

General threats to reptiles, and indeed all native wildlife, include:
  • It is estimated that between 1997 and 1999 in Queensland, 89 million reptiles were killed each year due to land clearing (Cogger et al. 2003)
  • Substantial habitat degradation by introduced species such as cattle and rabbits!
  • High levels of habitat modification caused by global climate change
  • death on roads.
  • Feral predators such as dogs, cats, pigs, and foxes.
  • The introduced cane toad may push this species into extinction.
  • Contamination and emerging diseases.

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