Reptilia · Squamata
Varanus olivaceusHallowell, 1857
Butaan
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 by Lythronax246, CC BY, via iNaturalist
A day-active, plant-eating monitor lizard from the Oriental region, reaching 730 mm snout to vent.
Also called Gray’s Monitor Lizard.
Once published as Varanus grayi — those names reach this page.
Reptilia › Squamata › Varanidae › Varanus
- Grows to
- 730mm
- greatest recorded
- Eats
- Herbivorous
- Active
- Diurnal
- Lives up to
- 17.6years
Longer than 81% 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
46 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
- Vulnerable
- Status assessed · the year the Red List last looked
- 2021
- Population trend
- Decreasing
- Red List criteria
- B1ab(iii,v)
The animal itself
- Limbs
- Four legs
- Fangs
- None
- Longest recorded life
- 17.6years
- Body temperature when active · measured in the wild
- 31.6°C89 °F
- Body temp in the wild · mean, when active
- 31.6°C
De Magalhaes & Costa 2009, Slavens and Slavens 1999: 15 and 2 months, Mendyk 2015 (17.6)
mean body temperature of active individuals in nature
body temperature of active animals in nature
Size
- Length snout to vent · greatest recorded
- 730mm2 ft 5 in
- Length snout to vent · adult female mean
- 517mm20.5 in
- Largest female · snout to vent
- 517.2mm20.5 in
- Hatchling length · snout to vent
- 129.8mm5 in
- Largest juvenile · snout to vent
- 129.8mm5 in
- Body mass · greatestcomputed
- 9159g20 lb
- Body mass · a typical adult
- 4141.4g9.1 lb
- Body mass · adult female, meanmeasured
- 1500g3.3 lb
- Body mass at hatchingmeasured
- 19.4g0.68 oz
max 730 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
AnAge rates this record "acceptable"
How it lives
- Diet
- Herbivorous
- Active
- Diurnal
- Where it lives
- Arboreal, terrestrial
- Habitat
- Forest
- Biome
- Tropical & Subtropical Moist Broadleaf Forests
- Active season · months of the year
- 12months
- Region
- Oriental
- Mainland or island
- Found only on islands
- Highest it lives · above sea level
- 400m
- Range size
- 26,652km²
- Density
- 0.03–0.61per hectare
- Home range · largest recorded
- 27,100m2
Herbivorous / Omnivorous (Perry and Garland, Zug et al. 2001, Cooper and Vitt 2002, Pianka and Vitt 2003, De Lisle 1996, Arbuckle 2009)/ juveniles eat invertebrates, adults eat fruit and invertebrates but are mostly frugivorous, eating mostly animal food only in the monsoon season (Pianka and King 2004)/obligatory fruit eater "supplemented with snails and hermit crabs" (Law et al. 2016), "Juveniles feed largely on snails and crabs but between the ages of 12-1 Rmonths the diet changes to include a large number of fruits. No other monitor lizard is known to feed on plant matter in the wild. but in Gray's monitor it forms a major part of the diet. Other important foods are snails. crabs, spiders, beetles, birds and their eggs." (Bennett 1995), fruit and invertebrates (Jenssen and Sy 2022)
(e.g., Jenssen and Sy 2022
Arboreal (Pianka and King 2004, Jenssen and Sy 2022)/Terrestrial / arboreal and terrestrial (Auliya and Koch 2020)
IUCN (0 to 400)
Breeding
- Reproduction
- Oviparous
- Sex decided by
- Genes, ZW/ZZ
- Average clutch
- 7.1eggs
- Eggs or young per clutch
- 3–16eggs
- Mean clutch
- 6–8.2eggs
- Clutches in a year
- 1.5per year
- Clutches a year
- 1per year
- First breeds at
- 24–36months
4-16, mean 8.2 (in captivity, Yufek 2012, also Auliya and Koch 2020), mean 17.6 (Du et al. 2014) - I had max as 16, max 11 (Bennett 1995)
Naming and history
- Suborder
- Sauria
- Infraorder
- Anguimoprha
- Subspecies
- No
- Described by
- Hallowell
- Moved to another genus · since it was first described
- No
- Described in
- 1857
- Type locality
- Philippines
Keeping one
Butaan is assessed as Vulnerable on the IUCN Red List. Species at risk in the wild are often covered by CITES and by national law, which decide what may be bought, sold, moved across a border or kept at all — and captive-bred and wild-caught animals are usually treated differently. Check the rules where you are before acquiring one. Nothing below is a judgement about keeping this species; it is what a published welfare standard says about space, and what the animal itself was measured doing.
9 ft 7 in × 9 ft 7 in × 9 ft 7 in(292 × 292 × 292 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 2 ft 5 in (730 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 89 °F (31.6 °C).
Mean body temperature of active individuals measured in nature. A measurement of the animal, not a setting for a thermostat.
Feeding
Prey size does not apply. A herbivore's diet is judged on fibre, on the ratio of calcium to phosphorus, and on avoiding plants high in oxalates.
The animal does not take prey items. This is established practice, not a measurement.
652kJ per day
Worked out for an animal of 9,159 g, the heaviest recorded for Butaan — 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
- — Preferred body temperature · chosen in a laboratory gradient
- — Eats arthropods
- — Eats vertebrates
- — Eats plant matter
- — How it hunts
- — 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
- — Active in
- — Lowest 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 olivaceus. Retrieved 2026-09-08, from https://www.allanglescreatures.com/species/varanus-olivaceus
@misc{varanus_olivaceus_2026,
title = {Varanus olivaceus},
author = {{The Reptile & Amphibian Encyclopedia}},
year = {2026},
url = {https://www.allanglescreatures.com/species/varanus-olivaceus}
}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.
- AnAge, Human Ageing Genomic Resources (de Magalhães et al.), used under CC BY 3.0.