Reptilia · Squamata
Varanus acanthurusBoulenger, 1885
Ridgetail Monitor
Identification not confirmed. One observer recorded this animal as this species and no one has since agreed, so the photograph may show a different animal.
Photograph placed in the public domain, CC0, via iNaturalist
A day-active, meat-eating monitor lizard from the Australo-Pacific region, reaching 250 mm snout to vent.
Reptilia › Squamata › Varanidae › Varanus
- Grows to
- 250mm
- greatest recorded
- Eats
- Carnivorous
- Active
- Diurnal
- Lives up to
- 20years
Longer than only 17% of all monitor lizards anyone has measured.
The bar is the rank itself: its length is the share of the family this animal exceeds. The chart below is the family’s real spread, on a logarithmic scale because body length here runs from 116.4 to 1,570 mm. The solid rule is this animal. Every bar is a count of real species, and nothing on this figure is estimated.
What is known
38 sourced facts, each taken from a named scientific dataset. How to read these.
Cited from a dataset unless a row is marked otherwise.
Standing in the world
- Still living
- Extant
- Conservation status
- Least Concern
- Status assessed · the year the Red List last looked
- 2017
- Population trend
- Stable
The animal itself
- Limbs
- Four legs
- Fangs
- None
- Longest recorded life
- 20years
10 (Carey and Judge 2000, Slavens and Slavens 1999, Mendyk 2015); 20 years (https://www.lllreptile.com/articles/179-ackies-monitor/ also https://thereptiletimes.wordpress.com/2013/11/12/caring-for-varanus-acanthurus-the-ackies-monitor-june-2013/)
Size
- Length snout to vent · greatest recorded
- 250mm9.75 in
- Length snout to vent · adult female mean
- 147.5mm5.75 in
- Largest female · snout to vent
- 147.5mm5.75 in
- Hatchling length · snout to vent
- 64.45mm2.5 in
- Largest juvenile · snout to vent
- 62.9mm2.5 in
- Body mass · greatestcomputed
- 286g10.1 oz
- Body mass at hatchingmeasured
- 6g0.21 oz
max 250 mm SVL (Feldman et al. 2016)
snout-vent length; the source column mixes this with straight carapace length
computed from length by a family-level allometric equation, not weighed
How it lives
- Diet
- Carnivorous
- How it hunts
- Sit and wait
- Active
- Diurnal
- Where it lives
- Saxicolous, terrestrial
- Habitat
- Grassland, Rocky, Savanna
- Biome
- Deserts & Xeric Shrublands
- Region
- Australo-Pacific
- Mainland or island
- Mainland
- Range size
- 3,077,081km²
Arthropods and lizards (e.g., "invertebrates (particularly orthopterans and beetles) and other lizards (geckoes, agamids and skinks)." (Bennett 1995), arthropods and small lizards (Auliya and Koch 2020, Black 1983)
e.g., Clemente et al. 2009
e.g., Doody et al. 2017, Auliya and Koch 2020
Saxicolous and Terrestrial / terrestrial (Clemente et al. 2009), terrestrial, arboreal and saxicolous (Auliya and Koch 2020)
Breeding
- Reproduction
- Oviparous
- Sex decided by
- Genes, ZW/ZZ
- Average clutch
- 9.3eggs
- Eggs or young per clutch
- 2–21eggs
- Mean clutch
- 7.5–11.1eggs
- Clutches in a year
- 1per year
- Clutches a year
- 1–3per year
- First breeds at
- 8–18months
mean 9.1 (Du et al. 2014), 1-6 mean 2.4, (Doody et al. 2017, but they don't trust it), 2-11 (Bennett 1995), 2-21 (Auliya and Koch 2020)
Naming and history
- Suborder
- Sauria
- Infraorder
- Anguimoprha
- Subspecies
- No
- Described by
- Boulenger
- Moved to another genus · since it was first described
- No
- Described in
- 1885
- Type locality
- Australia
Keeping one
3 ft 3 in × 3 ft 3 in × 2 ft 1 in(100 × 100 × 63 cm)
Minimum length × width × height, for one animal. Bigger is always better.
The standard sizes ground-dwelling species at 4 × 4 × 2.5 times snout-vent length.
Lives on rock, so stable hard surfaces and basking ledges suit it.
Mindestanforderungen an die Haltung von Reptilien (Sachverständigengutachten), German Federal Ministry for Nutrition, Agriculture and Forestry, Animal Welfare Division, 10 January 1997. The standard states these floor areas are recommendations rather than binding limits.
From this animal’s own snout-vent length of 9.75 in (250 mm), at 4 × 4 × 2.5 times it, following the German federal welfare standard — how this is worked out.
No preferred body temperature has been recorded for Ridgetail Monitor. Rather than repeat a number from a care sheet, this page leaves it out.
Feeding
A prey item should be no wider than the space between the animal's eyes.
Widely used across reptile husbandry references. The stated reason is that the gap approximates the width of the throat, so wider prey is associated with impaction. This is established practice, not a measurement.
30kJ per day
Worked out for an animal of 286 g, the heaviest recorded for Ridgetail Monitor — so it is the top of the range, not a figure for a particular animal. Weigh yours and the number will be lower.
An upper estimate, not a feeding target, and not veterinary advice. The equation covers only what an animal burns staying alive, so a growing, gravid or recovering animal needs more — and it was measured on wild animals, which move far more than one in an enclosure. Body condition and a vet who knows the species are what a feeding decision should rest on. Where this comes from.
Morphs
0 with peer-reviewed genetics behind them, 1 resting on breeder consensus. Most references present both with the same confidence.
- Red and yellow formsbreeder consensus
How red or yellow the ground colour is and how strongly the pale spotting shows. This follows the population an animal descends from rather than a gene, so pairing two red animals does not give a predictable proportion of red young.
What nobody knows
These are not gaps in our research. No scientific dataset records them for this species — and saying so is information you cannot get from a reference that simply leaves a field out.
- — Length snout to vent · adult male mean
- — Length snout to vent · adult mean
- — Length nose to tail · greatest recorded
- — Female length · mean, nose to tail
- — Length nose to tail · adult male mean
- — Length nose to tail · adult mean
- — Largest male · snout to vent
- — Largest female · shell length
- — Largest male · shell length
- — Hatchling length · nose to tail
- — Largest juvenile · shell length
- — Egg length
- — Egg width
- — Body mass · a typical adult
- — Body mass · adult female, mean
- — Preferred body temperature · chosen in a laboratory gradient
- — Body temperature when active · measured in the wild
- — Eats arthropods
- — Eats vertebrates
- — Eats plant matter
- — How the young develop
- — Gestation or incubation
- — Hatchling length · smallest recorded
- — Hatchling length · largest recorded
- — Age at first breeding · female
- — Mature from · youngest recorded
- — Mature by · oldest recorded
- — Size at maturity · smallest recorded
- — Size at maturity · largest recorded
- — Venomous
- — Body temp in the wild · lowest mean recorded
- — Body temp in the wild · highest mean recorded
- — Colour on the back
- — Pattern on the back
- — Pupil
- — Red List criteria
- — Active season · shortest recorded
- — Active season · longest recorded
- — Density · lowest recorded
- — Density · highest recorded
- — Home range · largest recorded
- — Active in
- — Lowest it lives · above sea level
- — Highest it lives · above sea level
Others in Varanidae
Take this data
Everything on this page is available as data under CC BY 4.0 — use it freely, credit it, no permission needed.
This species as JSON · the whole dataset
Cite this page
The Reptile & Amphibian Encyclopedia (2026). Varanus acanthurus. Retrieved 2026-09-08, from https://www.allanglescreatures.com/species/varanus-acanthurus
@misc{varanus_acanthurus_2026,
title = {Varanus acanthurus},
author = {{The Reptile & Amphibian Encyclopedia}},
year = {2026},
url = {https://www.allanglescreatures.com/species/varanus-acanthurus}
}Sources
- Meiri, S. (2024). SquamBase — a database of squamate (Reptilia: Squamata) traits. Global Ecology and Biogeography. Public domain (CC0).
- Oskyrko, O. et al. (2024). ReptTraits: a comprehensive dataset of ecological traits in reptiles. Scientific Data. Used under CC BY 4.0.
- Catalogue of Life (dataset 3LR), used under CC BY.