The Complete UK Millipede Substrate Guide: Depth, Moisture & What to Use
Start with the substrate. It's what a millipede eats and where it moults, and it's easy for new keepers to 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 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. 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. A moult that fails because the substrate was too shallow is an avoidable death.
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 a wide range 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 mixes British hardwood leaves, collected from Southern England woodland and naturally aged, with tougher bamboo leaves that hold their shape for longer, and our shredded rotten wood is a 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. For a ready-made base, our invertebrate substrate for isopods and millipedes is a forest floor mix in which nearly everything is something the animals can eat: lay it at least as deep as your longest millipede and cap it with leaf litter.
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
Millipedes build calcium into their exoskeleton, and most eat their cast skin after moulting, so keep a calcium source in permanently. 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 it is harder than cuttlebone, so it lasts longer in the tub 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 such as the Bumblebee millipede, at up to 45mm, that means 5 to 8cm. For something like a Ghana Speckled Leg, usually quoted at 16-18cm, 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
Moisture causes problems either way - 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 affects their food. The fungi and bacteria that break down leaves and wood slow sharply when the litter dries out, so the food in the tub decays far more slowly. Even a species that tolerates drier conditions, like the African Giant Chocolate, still needs a substrate that stays damp.
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. We leave softwoods out because conifer needles are tough, low in nutrients and slow to rot, and in feeding trials most millipedes and woodlice tested ate them least; conifer resins may also be harmful, though we have found no study that shows it. Stick to broadleaf hardwoods such as oak and beech.
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. 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 in a millipede substrate at all: it is not food, and for a millipede the bed is the food. If you already have some, a springtail culture is a better home for it than a millipede tub.
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 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 good millipede substrate is in our accessories range, and the listing for every species in our millipedes for sale collection covers the substrate it needs. If you're new to the whole thing and want a hand putting a setup together, we are always happy to talk it through, so do get in touch.
Frequently asked questions
What is the best substrate for millipedes? The best millipede substrate is a nutritious, forest-floor mix built on deciduous leaf litter and white-rotted hardwood, with a calcium source mixed through. These are the materials millipedes evolved to eat, and because the substrate is their primary food source, that nutritional content matters far more than how a substrate looks. A fermented-hardwood base such as flake soil, blended with leaf litter and crumbled rotting wood, suits a wide range of species.
How deep should a millipede's substrate be? As a rule, substrate depth should be at least equal to the length of your longest millipede, and deeper is rarely a problem. Depth matters because millipedes bury themselves completely to moult safely - too shallow, and moults can fail. A Bumblebee millipede, at up to 45mm, needs 5 to 8cm, while an African Giant Black, at up to around 33cm, needs a bed that deep.
Can I use coco coir for millipedes? We don't recommend coco coir in a millipede substrate. It holds moisture well, but it offers very little nutritional value, and since the substrate is your millipede's main food source, coir means building their home around something they can't really eat. Leave it out of the bed altogether: flake soil, white-rotted hardwood and organic topsoil hold moisture as well and feed the animal too.
Should millipede substrate have calcium in it? Yes. Millipedes build calcium into their exoskeleton, and most eat their cast skin after moulting, so keep a source in permanently. Mix ground cuttlebone or crushed oyster shell through the substrate, and leave a piece of cuttlebone on the surface for grazing.
How often should I change millipede substrate? Ideally you don't do full changes at all - you top up instead. Full substrate changes risk crushing moulting animals and throwing out eggs and tiny juveniles hidden in the substrate. Spot-clean mould and uneaten food, and add fresh leaf litter and rotting wood as the old material is eaten, so the enclosure refreshes itself.
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