Reptilia · Squamata
Varanus tristisSchlegel, 1839
Black-tailed Monitor
Photograph by dhfischer, CC BY, via iNaturalist
A day-active, meat-eating monitor lizard from the Australo-Pacific region, reaching 305 mm snout to vent.
Also called Black-headed Monitor, Freckled Monitor.
Once published as Varanus punctatus — those names reach this page.
Reptilia › Squamata › Varanidae › Varanus
- Grows to
- 305mm
- greatest recorded
- Eats
- Carnivorous
- Active
- Diurnal
- Lives up to
- 14years
Longer than only 31% 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
44 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
- 14years
- Body temperature when active · measured in the wild
- 34.15°C93 °F
- Body temp in the wild · mean, when active
- 31.8–36.5°C89–98 °F
Carey and Judge 2000, Slavens and Slavens 1999: 8 and 3 months, >12 (http://www.reptile-care.de/species/Anguimorpha/Varanidae/Varanus-tristis.html), 14 (Mendyk 2015)
mean body temperature of active individuals in nature
body temperature of active animals in nature
Size
- Length snout to vent · greatest recorded
- 305mm12 in
- Length snout to vent · adult female mean
- 231.2mm9 in
- Largest female · snout to vent
- 231.2mm9 in
- Hatchling length · snout to vent
- 67.5mm2.75 in
- Largest juvenile · snout to vent
- 69.5mm2.75 in
- Body mass · greatestcomputed
- 544.1g1.2 lb
- Body mass at hatchingmeasured
- 5g0.18 oz
max 305 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
- Mixed
- Active
- Diurnal
- Where it lives
- Arboreal, terrestrial
- Habitat
- Desert, Forest, Grassland, Rocky, Shrubland
- Biome
- Deserts & Xeric Shrublands
- Active season · months of the year
- 5–6months
- Region
- Australo-Pacific
- Mainland or island
- Mainland
- Elevation · above sea level
- 470–700m
- Range size
- 5,950,237km²
- Density
- 0.3–0.5per hectare
- Home range · largest recorded
- 400,000m2
vertebrates and invertebrates: lizards (Small agamids (Diporiphora spp.) and skinks (Ctenotus spp.,Carlia spp. - Sweet 2007), Arthropods, bird hutchlings, frogs and arthropods (Losos and Greene 1988), "Other lizards are their main prey, including other goannas, skinks, geckoes and agamids. They often swllow large agamids over a quarter of their own body weight and are able to swallow the heavily protected thorny devil, Moloch horridus. They also raid birds nests for eggs and Iledglings and collect a variety of invertebrates including orthopterans, beetles, ants and stick insects." (Bennett 1995), invertebrates and vertebrates (Cross et al. 2020), lizards birds and large insects (Auliya and Koch 2020)
Active foraging (e.g., Heatwole and Pianka 1993, Mesquita et al. 2016) / sit and wait (Clemente et al. 2009)
(e.g., Swan et al. 2017, Swan 2020), "from sunrise to near-dusk" (Shannon 2008), diurnal and nocturnal (Auliya and Koch 2020)
Arboreal and terrestrial (Sweet 2007), arboreal (Mesquita et al. 2016, Cross et al. 2020)/arboreal, sometimes saxicolous (Swan et al. 2017, Swan 2020), "predominantly tree based" (Shannon 2008), "largely arboreal, regionally terrestrial" (Auliya and Koch 2020)
Breeding
- Reproduction
- Oviparous
- Sex decided by
- Genes, ZW/ZZ
- Average clutch
- 9.1eggs
- Eggs or young per clutch
- 3–17eggs
- Mean clutch
- 8–10.2eggs
- Clutches in a year
- 1.5per year
- Clutches a year
- 1–2per year
- First breeds at
- 24months
mean 9.8 (Du et al. 2014), mean 9.95 (Mesquita et al. 2016), 6-17 (Bennett 1995)
Naming and history
- Suborder
- Sauria
- Infraorder
- Anguimoprha
- Subspecies
- Varanus tristis tristis (SCHLEGEL 1839) Varanus tristis orientalis FRY 1913
- Described by
- Schlegel
- Moved to another genus · since it was first described
- No
- Described in
- 1839
- Type locality
- Australia
Keeping one
4 ft × 4 ft × 4 ft(122 × 122 × 122 cm)
Minimum length × width × height, for one animal. Bigger is always better.
The standard sizes ground species at 4 × 4 × 2.5 and climbing species at 4 × 2.5 × 4 times snout-vent length.
Recorded both on the ground and climbing, so this is the larger of the two rules in every dimension.
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 12 in (305 mm), at 4 × 4 × 4 times it, following the German federal welfare standard — how this is worked out.
Active animals measured in the wild averaged 94 °F (34.2 °C).
Mean body temperature of active individuals measured in nature. A measurement of the animal, not a setting for a thermostat.
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.
53kJ per day
Worked out for an animal of 544 g, the heaviest recorded for Black-tailed 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.
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
- — 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
- — Colour on the back
- — Pattern on the back
- — Pupil
- — Red List criteria
- — Active in
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 tristis. Retrieved 2026-09-08, from https://www.allanglescreatures.com/species/varanus-tristis
@misc{varanus_tristis_2026,
title = {Varanus tristis},
author = {{The Reptile & Amphibian Encyclopedia}},
year = {2026},
url = {https://www.allanglescreatures.com/species/varanus-tristis}
}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.