Mertens' water monitor (Varanus mertensi)

Short answers

Mertens' water monitor: How big does the enclosure need to be?

Very large, at least 250×150×150 cm, of which at least 50 % a filtered water basin (water temperature ~28 °C).

Mertens' water monitor: What temperature does it need?

Daytime 28–32 °C (land section), basking spot 45–60 °C (hot basking spot), at night 22–26 °C.

Mertens' water monitor: Does it need UVB lighting?

UVB: UVB needed (Ferguson zone 3, UV index 3–5).

Mertens' water monitor: How long do they live?

Life expectancy: approx. 10–20 years.

Mertens' water monitor: Is it suitable for beginners?

No – better suited to experienced keepers (difficulty: Expert).

Climate

Daytime temperature

28–32 °C (land section)

Night temperature

22–26 °C

Basking spot

45–60 °C (hot basking spot)

Humidity

60–80 %

UVB

UVB needed (Ferguson zone 3, UV index 3–5)

Enclosure

Minimum size

very large, at least 250×150×150 cm, of which at least 50 % a filtered water basin (water temperature ~28 °C)

Substrate

Land section: sand-loam they can dig in; a large, deep water section with a powerful filter

Feeding

Food

Fish, crayfish or prawns, quail and quail eggs, occasionally rodents; a very strong feeding response

Feeding interval

adults 2–3×/week, juveniles (almost) daily

Key facts

Adult size

approx. 100 cm, up to 120–150 cm with the tail

Life expectancy

approx. 10–20 years

Origin

Northern Australia (rivers, lagoons, billabongs)

Protection status

CITES Appendix II / EU Annex B → registration required, proof of origin required

Brumation

no real winter rest; a slight seasonal drop or dry spell is possible

Cohabitation

Keep them singly; territorial, with an extremely strong feeding response and a risk of cannibalism. A pair only in a very large facility with visual barriers and supervision.

Notes

Entirely tied to water, and it dives to escape; a large, clean filter system is essential. In parts of its range it is badly threatened by cane toads (Bufo marinus). A common mistake: a water section that is too small or dirty.

Do you keep this species?

Add your animal to Reptoria – Reptoria reminds you about feeding and shedding. Add your animal for free →

Look for Mertens' water monitor (Varanus mertensi) in the marketplace →

Related species

• Argus monitor (Varanus panoptes) – Expert
• Bengal monitor (Varanus bengalensis) – Expert
• Blue tree monitor (Varanus macraei) – Expert
• Blue-tailed monitor (Varanus doreanus) – Intermediate to expert
• Finsch's monitor (Varanus doreanus finschi) – Expert
• Boatsi tree monitor (Varanus boatsi) – Expert
• Bogert's tree monitor (Varanus bogerti) – Expert
• Lace monitor (Varanus varius) – Expert

All species in the care wiki →

What you need to start

To keep Mertens' water monitor (Varanus mertensi) you typically need: a suitable enclosure (very large, at least 250×150×150 cm, of which at least 50 % a filtered water basin (water temperature ~28 °C)), substrate (Land section: sand-loam they can dig in; a large, deep water section with a powerful filter), a heat source with a thermostat, UVB lighting, thermometer and hygrometer, a water dish and hides. You will find equipment in the Reptoria marketplace.