How do I set temperature and humidity for my terrestrial tarantula?
Maintain a warm side at 80°F (27°C) and a cool side at 72°F (22°C), with humidity ranging from 50% to 70% depending on species, to keep your spider healthy.
Target numbers for a balanced enclosure
Aim for a daytime temperature of 80°F (27°C) on the basking side and 72°F (22°C) on the opposite wall. A night drop of 5°F (≈3°C) mimics natural cycles and helps prevent stress. Keep relative humidity between 50% and 70% for most terrestrial species, adjusting toward 80% if you keep an arboreal type.
Measure both temperature and humidity at the spider’s level, about 2 inches (5cm) above the substrate. Use a digital probe with a ±1°F (±0.5°C) accuracy and a hygrometer that reads to the nearest 1% RH. Record the readings twice daily for the first two weeks to spot drift.
- Warm side: 80°F (27°C)
- Cool side: 72°F (22°C)
- Night temp: 75°F (24°C)
- Humidity: 50‑70% RH
- Substrate depth: 2‑3 inches (5‑8cm)
Why a single temperature isn’t enough
Tarantulas are ectothermic; they move toward heat to digest and away from it to rest. A gradient lets them thermoregulate without human intervention, reducing the risk of metabolic slowdown.
If the enclosure is uniform, the spider may stay in one spot and become either sluggish or overheated. A gradient also encourages natural foraging behavior, as the spider will patrol between zones while hunting insects.
Humidity works the same way. A slightly moister micro‑zone near the hide helps with molting, while a drier area prevents fungal growth. Providing both zones lets the spider choose the optimal spot for each life stage.
Controlling temperature reliably
Install a low‑wattage ceramic heat emitter (5‑10W) on the warm side and plug it into a thermostat set to 80°F (27°C). Ceramic emitters stay cool enough to the touch, so you can leave them on for 12‑14hours without burning the substrate.
For the cool side, use a passive heat sink such as a dark wooden panel that absorbs ambient room heat. If the room temperature drops below 68°F (20°C), add a 25‑W under‑tank heater set to 70°F (21°C) and monitor with a second probe.
Always place a thermostat probe at the spider’s level on the warm side, not on the glass, because glass can read 5‑10°F (≈3‑6°C) higher than the actual air.
- Ceramic heat emitter: 5‑10W
- Thermostat setpoint: 80°F (27°C)
- Under‑tank heater (optional): 25W
Managing humidity without mold
Choose a dry substrate like coconut fiber or peat moss, then mist it lightly with a spray bottle to reach 60% RH. A 1‑inch (2.5cm) layer of moss in the hide adds localized moisture without saturating the whole floor.
Add a small ventilation slot (¼‑inch wide) near the top of the enclosure to allow excess moisture to escape. If humidity falls below 50%, place a shallow water dish (2×2inches, 100ml) on the cool side and mist the moss twice daily.
Use a hygrometer with a built‑in probe that can be tucked under a hide. Check the reading after each mist; if it spikes above 75%, increase ventilation or replace the moss with a drier layer.
- Moss depth: 0.5‑1 inch
- Vent slot width: ¼ inch
- Water dish volume: 100ml
Signs the numbers are off
If the spider spends all day on the cool side and refuses to eat, the warm side may be below 78°F (25°C) or the humidity too high (>80%). Check for a thin, papery exoskeleton after a molt, which signals low humidity.
Conversely, if you see the spider basking constantly, legs twitching, or the enclosure feels sticky, the temperature may exceed 85°F (29°C) or humidity may be above 75% for extended periods.
Regularly inspect the molting site; a successful molt with a clean shed indicates the gradient and moisture are within target ranges. Adjust the thermostat by 2°F (≈1°C) or add a vent slit of ½‑inch if problems persist.
Keep reading about Tarantula: Tarantula care sheet
Related questions
Can I use a heat lamp instead of a ceramic emitter?
A heat lamp can raise the warm side to 85°F (29°C) quickly, but it also dries the air. If you choose a lamp, lower the wattage to 15‑20W and add a misting schedule of three 5‑second sprays per day to keep humidity above 50%.
How often should I replace the substrate?
Replace the substrate every 6‑12months, or sooner if you notice a persistent odor or mold. A fresh 2‑inch layer restores proper drainage and helps maintain stable humidity.
Do I need a night‑time heat source?
No. Allow the temperature to drop 5°F (≈3°C) after sunset; most species thrive at 75°F (24°C) overnight. If your room stays below 65°F (18°C), a low‑wattage under‑tank heater set to 70°F (21°C) will prevent a dangerous chill.
Not veterinary advice. This guide covers husbandry — housing, feeding, cleaning and handling. If your tarantula is injured, off food unusually long, or behaving abnormally, contact a veterinarian.