The Complete UK Millipede Substrate Guide: Depth, Moisture & What to Use

If you get one thing right with millipedes, make it the substrate. Not the enclosure, not the heating, not the décor — the substrate. It's the single most important part of keeping millipedes successfully, and it's the thing new keepers most often get wrong.

The reason is simple: with millipedes, the substrate is the food. Unlike a reptile or an amphibian that you feed separately, a millipede spends most of its life burrowing through and eating the material it lives in. Get the substrate right and your millipede has a constant, slow-release food source, somewhere safe to moult, and stable humidity. Get it wrong and no amount of cucumber on the surface will save it.

This guide covers what millipede substrate actually needs to do, the mix we recommend, how deep it needs to be, how to manage moisture, and — because it comes up constantly — what to avoid.

What millipede substrate has to do

A good millipede substrate is doing three jobs at once:

It feeds them. Millipedes are detritivores. In the wild they live on the forest floor eating decaying leaves and rotting wood, breaking down tough plant cellulose into the nutrient-rich frass that enriches woodland soil. A substrate that's just bedding — something inert they sit on — will slowly starve them, even if it looks fine.

It lets them moult safely. This is the part most people underestimate. Millipedes burrow down into the substrate to moult, sealing themselves into a chamber while their new exoskeleton hardens. During this period they're soft, vulnerable, and completely dependent on having enough depth to bury themselves properly. A moult that fails because the substrate was too shallow is one of the most common avoidable deaths in the hobby.

It holds humidity. A deep, slightly damp substrate acts as a moisture reservoir, keeping the lower layers humid while the surface dries a little. That gradient is what allows a millipede to self-regulate — moving down when it wants moisture, up when it wants air.

The substrate mix we recommend

There's no single "correct" recipe, and you'll see plenty of variation between experienced keepers. But a reliable mix that works for the vast majority of species looks something like this:

• 50% deciduous leaf litter humus — broken-down leaves from oak, beech and similar hardwoods
• 20% partially decomposed leaves — aged, brown, starting to break down
• 20% crumbled white-rotted hardwood — soft enough to crumble between your fingers
• 5% play sand or bird grit — not builder's sand
• 5% ground cuttlebone or limestone — for calcium

The two non-negotiable ingredients are leaf litter and rotting wood. These are what millipedes evolved to eat, and they should make up the bulk of any mix. Our leaf litter is a birch, maple and oak blend collected from Southern England woodland and naturally aged, and our shredded rotten wood is a properly white-rotted hardwood mix, frozen to eliminate pests before it reaches you. If you'd rather start with something pre-mixed, our flake soil — fermented oak and beech, originally developed for beetle larvae — makes an excellent primary substrate for millipedes and works well blended into the mix above.

A quick word on the rotting wood, because it matters: it needs to be white-rotted. That means pale, crumbly, soft, with a clean earthy smell. If it's dark orange, still hard, or smells of anything other than soil, it's either the wrong type of decay or it's softwood — and softwood is a problem, which we'll come to.

A note on calcium

Calcium isn't optional for millipedes. Their segmented exoskeleton is calcified, and they add new segments with every moult throughout their lives, so the demand is constant. You can mix ground cuttlebone or crushed oyster shell directly into the substrate, and it's worth leaving a piece of cuttlebone on the surface too so they can graze as needed. Oyster shell is particularly handy for burrowing species because it mixes through the substrate and releases slowly without fouling anything.

How deep should millipede substrate be?

The rule worth memorising is this: substrate depth should be at least equal to the length of your longest millipede. Some keepers go deeper, and deeper is rarely a problem.

The reason is moulting. A millipede needs to bury itself completely to moult safely, and it can't do that in shallow substrate. For a small species this might mean 8–10cm. For something like a Ghana Speckled Leg at 18–19cm, you're looking at a serious 18–20cm of substrate, which has real implications for how you choose and set up the enclosure. Factor this in before you buy the animal, not after.

A useful way to layer it: compact the bottom two-thirds of the substrate slightly to hold moisture and structure, then add the top third more loosely so they can dig into it easily. Finish with a generous layer of whole leaves and a few chunks of rotting wood on the surface.

Managing moisture

Most millipede problems come down to moisture being wrong — either too wet or too dry.

You're aiming for substrate that's moist to the touch but not waterlogged. A simple test: squeeze a handful. It should hold together and feel damp, but not drip water. If you can wring water out of it, it's too wet.

The ideal is a gradient — damp in the lower layers, drying out a little towards the surface. This lets the millipede choose its own conditions. Mist when the top layer starts looking dry, but resist the urge to keep everything constantly soaking. Stagnant, waterlogged substrate causes two problems: it encourages mould, and in some species it leads to a bacterial condition affecting the legs sometimes called "foot rot."

There's an important detail that catches people out, particularly with the drought-tolerant species. A completely dry substrate isn't just uncomfortable — it means the millipede can't feed. Their mouthparts aren't strong enough to chew hard, bone-dry wood and leaves. Humidity keeps the food soft enough to eat. So even a species that tolerates drier conditions, like the African Giant Chocolate, still needs reliable access to moisture to eat properly.

Good ventilation works with moisture rather than against it. Cross-ventilation — airflow moving across the enclosure — prevents the stale, stagnant conditions that breed mould, while a deep damp substrate keeps humidity where it needs to be. Our screw-in air vents are an easy way to get stable airflow without resorting to glued organza or hand-drilled holes.

What to avoid

Softwood and conifers. Never use anything from pine, spruce or other conifers — needles, wood, or bark. Softwoods contain resins and aromatic oils that are harmful to millipedes, they decompose differently, and most millipedes can't digest them anyway. Stick to broadleaf hardwoods: oak and beech are the gold standard.

Soil from the garden, or anything with pesticides or fertilisers. If you're using topsoil, it needs to be organic, pesticide-free and fertiliser-free. Garden soil can carry chemical residues and unwanted hitchhikers.

Coco coir as the main ingredient. This one comes up a lot, so let's be clear. Coconut coir is widely sold as a reptile and invertebrate substrate, and it holds moisture well, but it offers very little nutritional value to a millipede. Since the substrate is your millipede's primary food source, building it around coir means building it around something they can't really eat. We don't recommend coir as the foundation of a millipede substrate. If you already have some and want to use it up, the only sensible way is to mix it through with plenty of leaf litter and rotting wood so it's a minor component of a nutritious whole — never the bulk of it.

Bone-dry "set and forget" setups. Millipedes aren't a fill-it-once animal. The substrate gets eaten, so it needs topping up. When it starts looking more like plain soil and less like a forest floor — leaves gone, wood broken down — it's time to add more leaf litter and rotting wood.

Maintenance: topping up, not tearing down

Because the substrate is food, the best approach to maintenance is to top up rather than replace. Full substrate changes are disruptive and risky — millipede eggs and tiny juveniles hide in the substrate and are very easily missed and thrown out, and a moulting millipede buried somewhere in there has a soft body that's easily crushed.

Instead, spot-clean any mould or uneaten fresh food, and regularly add fresh leaf litter, rotting wood and a little substrate to the top. The colony refreshes itself as the new material works down and the old material gets eaten. If you ever do need to dig through the substrate, do it slowly and check every handful before discarding it.

The short version

Get the substrate right and millipede keeping becomes genuinely easy. Use a leaf-litter-and-rotting-wood base with calcium mixed in, make it deep enough for your animal to bury itself completely, keep it damp but not waterlogged with a bit of airflow over the top, and avoid softwood and nutritionally empty fillers. Top it up rather than replacing it, and leave the animals to get on with it.

Everything you need for a proper millipede substrate is in our accessories range, and every species in our millipedes for sale collection ships with care notes covering its specific substrate needs. If you're new to the whole thing and want a hand putting a setup together, our live chat is always happy to talk it through.