Millipede Substrate Guide
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Substrate is one of the most important parts of a millipede enclosure. Millipedes don't simply walk on their substrate. They live in it, burrow through it, feed on it, molt in it, and lay their eggs in it.
For many commonly kept millipedes, the substrate itself makes up a significant portion of their diet. Supplemental foods such as fruits and vegetables should not replace a nutritious substrate rich in decomposing hardwood and leaf litter.
Building a Good Millipede Substrate
A good general-purpose substrate for many commonly kept tropical millipedes can consist of approximately:
- 50–70% edible material — Well-rotted deciduous hardwood, quality flake soil, decomposed hardwood leaves, or a combination of these.
- 20–30% organic topsoil — Helps provide structure and retain moisture. Choose one without fertilizers, pesticides, perlite, or other additives. Avoid coconut coir.
- 10–20% decomposed leaf litter — Hardwood leaves such as oak are excellent additions and provide another natural food source.
These percentages are guidelines rather than strict requirements and can be adjusted for individual species.
Rotten Wood & Flake Soil
Well-rotted hardwood is an important food source for many millipedes. Suitable wood should be soft, decomposed, and easily crumbled by hand rather than fresh wood chips or sawdust.
Oak and other safe deciduous hardwoods are commonly used.
Flake soil is another option. It is fermented hardwood sawdust that has been partially broken down through microbial activity, producing an edible substrate used extensively for detritivorous invertebrates. It can be mixed with rotten wood and leaf litter or used as a major component of the substrate.
When collecting rotten wood outdoors, only collect material when you can confidently identify the tree and know the area has not been exposed to pesticides or other contaminants.
Avoid aromatic softwoods such as cedar and pine, particularly fresh material, as their aromatic compounds can be harmful to invertebrates.
Leaf Litter
Leaf litter is both food and habitat.
A generous layer of dried hardwood leaves should be kept over the substrate. As the leaves begin to decompose, millipedes will gradually consume them.
Oak leaves are an excellent choice because they are readily available, decompose gradually, and provide long-lasting cover.
Additional leaves can simply be added as the previous layer is consumed.
Avoid leaves collected from roadsides, chemically treated lawns, or areas where pesticides and herbicides may have been applied.
Calcium
Millipedes have mineralized exoskeletons, so providing access to calcium is a useful part of captive husbandry. Calcium can be scattered across the substrate or mixed into the substrate.
Common calcium sources include:
- Cuttlebone
- Calcium carbonate
- Crushed oyster shell
- Limestone
Moisture
Millipede substrate should generally remain damp but not waterlogged, but this will vary from species, to species.
A useful comparison is a wrung-out sponge. When squeezed, the substrate should feel noticeably moist and hold together without releasing large amounts of water.
The exact moisture level depends on the species being kept. Some tropical species prefer consistently moist conditions, while others benefit from a stronger moisture gradient.
Rather than relying entirely on misting, occasionally check the substrate several inches below the surface. The deeper substrate should retain moisture even when the very top begins to dry.
Good ventilation is equally important. Constantly saturated substrate with inadequate airflow can encourage undesirable microbial growth and create poor conditions underground.
Substrate Depth
Millipedes need enough substrate to completely bury themselves. A useful rule is to provide substrate at least as deep as the millipede is long, with deeper substrate preferred.
Adequate depth is particularly important because millipedes commonly retreat underground to molt, rest, and reproduce. It is normal to not see your millipedes for extended periods of time, never dig them up.
Refreshing the Substrate
Millipede substrate is gradually consumed.
Over time, decomposed wood and leaves are converted into frass and the amount of edible material decreases. Fresh rotten hardwood, flake soil, and leaf litter should therefore be added periodically.
Instead of routinely replacing the entire enclosure at once, partially refresh the substrate by removing some of the oldest material and mixing in fresh edible substrate.
This is especially important in breeding colonies. Eggs and newly hatched millipedes can be extremely small and easy to overlook, so discarded substrate should always be inspected carefully.
How frequently substrate needs refreshing depends on the number and size of millipedes, enclosure size, and how quickly the edible material is being consumed.
Avoid Using
- Fresh or aromatic softwoods, especially cedar
- Dyed, preserved, or chemically treated wood
- Soil containing fertilizers or pesticides
- Potting mixes containing chemical additives
- Coco coir
- Pure soil as the sole substrate
- Sand or gravel as the primary substrate
The most important thing to remember is that millipede substrate is also food.
A substrate that simply holds humidity is not necessarily a nutritious substrate. For many commonly kept species, maintaining a substantial amount of decomposed hardwood, flake soil, and decomposed leaf litter, often around 50–70% of the substrate is a good husbandry target.
