There is no single humidity percentage that suits all millipedes. What matters most is that the substrate stays consistently moist below the surface, while remaining loose, breathable and never waterlogged. Species differences matter, but the enclosure floor is always more important than a number on a gauge.
What millipedes need from their enclosure
Millipedes are substrate-dependent animals. They spend much of their time in the enclosure floor itself, burrowing to rest, stay secure, regulate moisture and, for many species, moult safely. That means the conditions under the surface matter more than how humid the air feels above it.
A good setup should feel like a stable woodland floor: deep, organic substrate with leaf litter and decomposing wood helping it hold moisture naturally. The bedding should be damp and earthy, not muddy or soggy, and deep enough to stay usable for burrowing. For a broader setup overview, our Millipede Enclosure & Substrate Guide and Millipede Setup & Substrate Guides are a good place to start.
Different species come from different habitats, so some prefer a wetter, more enclosed setup while others do better with more airflow and carefully maintained dampness. If you know the species, its specific requirements should always come before any general humidity target.
Everyday care
Rather than chasing a fixed reading, think in terms of consistency. Millipedes usually do best when the substrate stays evenly moist below the surface, with a little variation across the enclosure so they can choose the conditions they prefer. In nature, the top layer may dry slightly while the lower layers remain damp, and a good enclosure should reflect that pattern.
Check the substrate in a few places. The surface may be lightly dry in parts, but beneath that it should still feel cool and damp. If the lower layers are drying out, the enclosure needs more moisture. If the bedding feels sticky, compacted or starts to smell sour, it is too wet.
Leaf litter, decaying leaves and rotting wood all help hold moisture and create a more natural microclimate, so they should be part of the main substrate structure rather than treated as decoration. That combination gives millipedes a stable, breathable layer to burrow into and helps the enclosure hold moisture for longer.
Misting can help maintain surface moisture, but it is only part of the picture. The substrate does the real work. If you want practical timing tips, see How Often Should You Mist a Millipede Enclosure?
Ventilation also matters. Millipedes need damp conditions, but they should not be kept in stagnant air. Some airflow helps prevent the enclosure from becoming sour or overly wet. The right balance depends on the setup, so it is worth reading Do Millipedes Need Ventilation?
Feeding and moisture routines can overlap, but fresh food should not be used to make up for dry bedding or poor substrate. Millipedes get much of their long-term nutrition from the organic material in the enclosure itself, so a well-prepared habitat does more than simply hold water.
A mature enclosure is usually easier to manage than a newly set up one. As leaf litter and wood begin to break down, the habitat becomes more stable and better at holding moisture.
Common mistakes
The most common mistake is treating humidity as the main target and ignoring the substrate underneath. A misted enclosure with thin bedding may look damp for a short time, but it will not hold the right conditions for long. At the other extreme, overwatering can leave the substrate muddy, compacted or sour. Millipedes need moisture, but they also need air spaces in the substrate so they can burrow and breathe comfortably.
Keeping the enclosure too dry causes problems just as quickly. This is especially likely in shallow setups or enclosures with too much ventilation and too little organic material. If the lower layers dry out completely, millipedes lose the stable moisture they depend on.
If you are unsure whether your substrate has crossed from damp into too wet, this guide will help: How to Tell if Millipede Substrate Is Too Wet
When humidity and substrate balance are right, the enclosure usually settles into a steady rhythm. The top layer may be lightly dry in places, but beneath that the substrate remains moist and earthy, leaf litter slowly breaks down, and the millipedes can burrow and reappear on their own terms. In practice, that means moist substrate, not a wet enclosure; stable conditions, not constant changes; and species-aware care, not one universal number.
