Substrate Safety & Setup

Substrate IS the diet

Unlike most pets, millipedes eat their substrate. They're detritivores, feeding on decaying organic matter, so the substrate in their enclosure is their main food source. If it's nutritionally poor, the millipede will slowly starve even in what looks like a perfectly set-up enclosure.

Think of it as a living ecosystem, not just bedding. You want decaying hardwood, leaf litter, and the microbial communities that help break those materials down.

Substrate composition

A good millipede substrate is a mix of several components:

• Organic topsoil, free from fertilisers, pesticides, and herbicides. Read the label
• Well-rotted hardwood. Oak and beech are ideal. Include pieces and shavings at various stages of decay
• Dried leaf litter. Oak and beech leaves work well. Collect from areas that haven't been sprayed
• Sphagnum moss to help keep moisture levels up throughout the substrate
• Coco coir as a base. Holds moisture well and gives the mix some structure

Mix everything together well. You're aiming for something that looks and feels like rich forest floor: dark, crumbly, and slightly damp.

Calcium

Millipedes have heavily calcified exoskeletons, some of the most mineralised of any arthropod. Without enough calcium, moults fail. And a failed moult is usually fatal.

Provide calcium in multiple forms:

• Cuttlebone. Break into pieces and mix into the substrate, and leave pieces on the surface
• Crushed eggshell. Wash, dry, and crush before adding
• Crushed oyster shell. Available from poultry supply shops
• Limestone pieces. Small chunks buried in the substrate

Put calcium both mixed into the substrate and on the surface. They'll seek it out and eat it when they need it, especially around moult time.

Toxic substrates

Cedar, pine, spruce, and ALL softwoods contain phenols and terpenes that are toxic to millipedes. This isn't a "maybe they won't like it" situation. Softwood exposure can kill them.

Specifically avoid:

• Cedar shavings or chips
• Pine bedding or shavings
• Any commercial small-animal bedding made from softwood
• Spruce, fir, or any other conifer wood

Only use hardwood. Oak, beech, birch, and other deciduous species are safe. If you're not sure about a wood type, leave it out.

Substrate depth

Give them at least 10–15 cm of substrate for most species, 20 cm or more for large species like Archispirostreptus gigas. Millipedes burrow down to moult, and during that time they're at their most vulnerable, with a soft new exoskeleton that needs time to harden.

If the substrate is too shallow, they're forced to moult near the surface where they can dry out or get disturbed. Depth gives them the safety they need.

Moisture

The substrate should be damp throughout. Squeeze a handful and it should hold together but not drip. Spray regularly with dechlorinated water, and pay extra attention to spots that dry out faster like near ventilation holes or under heat sources.

Dry substrate kills millipedes. They breathe through spiracles and need moisture to function. Desiccation is one of the most common causes of death in captivity. When in doubt, go slightly too wet rather than too dry.

Rotting wood pieces

Bury several chunks of white-rotted hardwood in the substrate. These soft, crumbly pieces of decaying wood are one of their main food sources, and they'll graze on them constantly. This isn't decoration. They need it.

Replace the wood as it gets eaten. You'll notice the pieces gradually shrinking and crumbling away.

When to refresh substrate

Top up leaf litter and rotting wood as it gets consumed. Every 3–4 months, do a partial substrate change, replacing about a third of the old material with fresh.

Never replace all the substrate at once. The established microfauna (springtails, beneficial mites, fungi, bacteria) are part of the ecosystem your millipedes depend on. Ripping that out stresses the animals. Gradual refreshes keep things nutritionally sound without wrecking the microbial community.