Decor
- Lots of branches for climbing through the height
- Dense foliage for cover
- Water bowl on the cool side — for drinking
Monitor lizards · Care guide
Yellow Tree Monitor Care Guide
Varanus reisingeri
Native to Misool Island, Indonesia, this dwarf monitor barely exceeds 3 ft and lives in the rainforest canopy, using a prehensile tail among branches and dense foliage in high humidity.
At a glance
Quick facts
Key parameters for day-to-day husbandry. Full detail is in the sections below.
-
Daytime probe
80–82 °F
27–28 °C · halfway down the back
-
Night
~70 °F
21 °C · evening set point
-
Humidity
70–90%
Day can sit in the 70s · night spike
-
UVB
T5 6%
Ceiling-mounted tube
01 · Housing
Enclosure & housing
A vertical, high-humidity vivarium. Youngsters are a darker uniform green; adults take on a lemon-and-lime colour with a more yellowish hue. They rarely come down to the forest floor, so branches and dense foliage come first.
Adult minimum size
48″ W × 24″ D × 48″ H
4 ft × 2 ft × 4 ft high, or larger, for a single adult. They barely exceed 3 ft. Babies can start in something smaller.
Substrate
- Humidity-retentive mix
- Orchid bark mixed with coir, coir on its own, or a bio mix
Cleaning
- Daily: spot clean to keep the enclosure fresh and limit bacteria
- About every six weeks: if kept relatively clean — discard substrate, disinfect décor and the vivarium, add fresh substrate, and return clean, dry décor
Housing diagram
Enclosure example
Front view 48″ wide × 48″ tall (depth 24″) · branches · dense foliage · cool-side water bowl
- Front proportions — 48″ wide × 48″ tall (1:1); depth 24″ — 4 × 2 × 4 ft
- Branches — climbing wood for a canopy lifestyle
- Foliage — dense cover through the height
- Water bowl — cool side, for drinking
- Substrate — orchid bark mixed with coir, coir alone, or a bio mix
- Heat & UV — basking around 95 °F (35 °C) · T5 6% on the ceiling
Setup diagram · 1 of 2
Top-down view
Heat bulb & probe left–right positions · Recommended temps need this layout
Setup diagram · 2 of 2
Front view
Looking into the vivarium · bulb on the ceiling · probe hangs down the back
- Heat bulb — about one-quarter from one side, halfway front to back (on / through the ceiling)
- Probe — one-quarter from the opposite side, hanging down the back about halfway down
02 · Climate
Temperature & UVB
A tall arboreal setup, a clear gradient, T5 6% UVB, and humidity averaging 70–90% with a night spike.
Daytime temperature gradient
When the heat bulb and thermostat sensor are placed as instructed, a probe target of 80–82 °F (27–28 °C) creates this spread. The probe point is not the basking spot.
| Zone | Temperature |
|---|---|
| Cool side | ~78 °F (~26 °C) |
| Probe point (thermostat probe target) | 80–82 °F (27–28 °C) |
| Middle | 84–86 °F (29–30 °C) |
| Warm side | 88–90 °F (31–32 °C) |
| Basking spot (hottest point under bulb) | ~95 °F (~35 °C) |
| Night drop | Reduce thermostat by turning it down to around 70 °F (21 °C) |
Photoperiod & night
- Winter: about 12 hours of light and heat
- Summer: up to 16 hours when days are longer
- Night: turn the thermostat down to around 70 °F (21 °C)
- A clear day and night lets metabolism slow so the body can rest
UVB lighting
- A T5 unit with 6% UV output, mounted on the ceiling
- Straight across, or diagonally so the power unit sits toward a rear outlet or vent
- Replace every 12 months — UV output degrades over time
- Match UV on and off to the heat schedule (morning on, evening off)
- UVA supports appetite and activity; UVB enables vitamin D3 and calcium absorption
Humidity & water
Keep an average of 70–90% humidity. Daytime can drop into the 70s, but the night spike still matters. Spray twice a day. A fogger or spray system helps raise humidity gently. Place a water bowl on the cool side.
Day
70s
Can sit toward the lower end
Night
Spike
Within the 70–90% average
- Spray twice a day — a fogger or spray system helps raise humidity gently
- Cool-side water bowl for drinking
- Treat water with a de-chlorinator such as Reptishield, or use bottled water — never untreated tap
Climate diagram
Lighting setup
T5 6% UVB on the ceiling · heat on the warm / basking side
- T5 6% UV unit — ceiling-mounted (straight or diagonal); UVA supports appetite & activity; UVB enables vitamin D3 / calcium absorption
- Heat dome — warm side; basking ~95 °F (35 °C); same on/off routine as UV (morning on, evening off)
- Photoperiod — 12 hours in winter, up to 16 hours in summer
- Replace UV every 12 months — output degrades even if the tube still glows
First power-up tip
Always have the thermostat dial turned down before you plug it into the mains for the first time.
03 · Nutrition
Diet & feeding
Insect-led, with pinkies or small mice once or twice a week and scrambled egg occasionally. Dust every feed, gut-load well, and use the method of 5 while settling.
At a glance
Feeding cheat sheet
- Method
- Method of 5 while settling · hunting in the enclosure
- Settled
- Often 10–20 crickets daily
- Adults
- Appetite drops — 1–2 food-free days a week is often needed
- Staples
- Crickets, locusts, Dubia, calci worms · vegetables (most will not eat them)
- Also
- Pinkies or small mice 1–2× a week · scrambled egg occasionally
- Dust
- Every feed · 4:1 calcium : Nutrobal
- Water
- Cool-side bowl · Reptishield or bottled · never untreated tap
Staples
Feed regularly · dust every feed
- Crickets, locusts, Dubia roaches
- Calci worms
- Vegetables — most will not eat them
Moderation & extras
Not every day
- Wax worms, mealworms, Morios — in moderation
- Pinkies or suitably sized small mice, once or twice a week
- Scrambled egg occasionally
Supplements — every feeding
Before offering live food, coat it with a 4:1 mix of calcium to Nutrobal (4 parts calcium to 1 part Nutrobal). Mix the powders first, then dust every feed.
Settling appetite — method of 5
A new monitor is often stressed and may not eat well for the first few days. That is normal. Until you know its habits, use the method of 5: offer five insects at a time and wait until they are eaten before adding more. That avoids leaving 10 or 15 insects in the vivarium, which can stress the animal and cause injuries. Once settled and eating well, 10–20 crickets a day is relatively common. As they reach adult size, appetite drops, and one or two food-free days a week are often needed.
Feeding style
- Hunting and chasing food is vital — exercise and enrichment
- Hand feeding can help bonding — too much can lead to obesity
Water
- Cool-side water bowl so the monitor can drink
- Reptishield or bottled water only — never untreated tap
Why gut loading matters
Feeder insects need a varied diet before you offer them. In the wild, monitors eat prey that has itself eaten widely, which supplies nutrients and a better calcium-to-phosphorus balance. A tub of crickets with only a piece of carrot or potato is a poor Ca:P ratio and a thin vitamin source.
- Use commercial gut-load foods with a wide ingredient list
- Add fresh vegetables suitable for reptiles for more variety
- The broader the insects’ diet, the better fed your monitor will be
04 · Behaviour
Handling & behaviour
A dwarf arboreal monitor, barely over 3 ft, that spends most of its time in the branches. Settling and regular feeding come before handling.
- Step 1
Settle first
A new home is stressful, and early handling can make that worse. Wait until the monitor is eating regularly before you start.
- Step 2
Short sessions
Initial sessions: 5–10 minutes only. Lengthen them as the monitor becomes more comfortable.
- Hygiene
Wash hands
Wash or disinfect hands before and after handling so bacteria are not passed either way.
- Warning
No aerosols
Do not use aerosols or plug-in air fresheners near the enclosure — the chemicals can harm your Yellow Tree Monitor.
05 · Welfare
Health & welfare
Prevention starts with correct husbandry — heat, UVB, hydration, and supplementation working together. If something seems wrong, contact the team before changing the setup.
Best prevention: good husbandry
Correct temperatures, supplementation, hydration, and UVB keep the immune system and gut working well. In captivity the animal only has what you provide.
Inert substrates Paper, lino, carpet — pros and cons
Pros
- Lower impaction risk
Cons
- Limit natural behaviours such as digging
- Can increase faecal contamination, because waste is less absorbed
Questions
FAQ
What size vivarium does a Yellow Tree Monitor need?
For a single adult, a minimum of 48″ wide × 24″ deep × 48″ tall (4 × 2 × 4 ft), or larger. They barely exceed 3 ft, but they live in the canopy, so height, branches, and dense foliage matter. Babies can start in something smaller — you will find it easier to interact with a baby without chasing it around a large vivarium.
What temperatures does a Yellow Tree Monitor need?
Set the thermostat probe to 80–82 °F (27–28 °C) with the heat bulb about one-quarter from one side, halfway front to back, and the sensor one-quarter from the opposite side, hanging down the back about halfway down. That creates about 78 °F on the cool side, 84–86 °F in the middle, 88–90 °F on the warm side, and a basking spot generally around 95 °F under the bulb. At night turn the thermostat down to around 70 °F (21 °C). Use about 12 hours in winter and up to 16 hours in summer.
What humidity do Yellow Tree Monitors need?
Aim for an average of 70–90%. Daytime can drop into the 70s, but you still need the night spike. Spray twice a day. A fogger or spray system helps raise humidity gently. Use a humidity-retentive substrate — orchid bark mixed with coir, coir on its own, or a bio mix — and a cool-side water bowl. Always treat water with a de-chlorinator such as Reptishield, or use bottled water. Never use untreated tap water.
When can I start handling my Yellow Tree Monitor?
Let it settle in the new vivarium first. Once it is eating regularly, you can start short sessions of 5–10 minutes and lengthen them as it becomes more comfortable. Always wash or disinfect your hands before and after handling. Do not use aerosols or plug-in air fresheners near the enclosure.
What UVB do Yellow Tree Monitors need?
A T5 unit with 6% UV output, mounted on the ceiling — straight across or diagonally so the power unit sits toward a rear outlet or vent. Replace the tube every 12 months, because UV output drops even if the tube still lights. Switch UV on and off with the heat: about 12 hours in winter and up to 16 hours in summer. UVA supports appetite and activity; UVB lets the body make vitamin D3 so calcium can be absorbed.
What do Yellow Tree Monitors eat?
Staples are crickets, locusts, Dubia, and calci worms, plus vegetables — though most will not eat the vegetables. Wax worms, mealworms, and Morios are for moderation. Pinkies, or suitably sized small mice, once or twice a week, and scrambled egg occasionally. Dust every feed with a 4:1 calcium to Nutrobal mix. Use the method of 5 while settling. Once eating well, 10–20 crickets a day is relatively common; adults often need one or two food-free days each week. Hunting and chasing food matters. Hand feeding can help bonding, but too much of it can lead to obesity.
Next steps
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