There isn't a universal stocking number for millipedes. How many can live together depends on the species, adult size, enclosure footprint and substrate depth, as well as how much food and shelter the setup can actually support.
In practice, millipedes are often kept in small groups successfully, but only when the enclosure is built to suit them. A roomy, deep substrate setup with plenty of leaf litter and decaying wood gives them space to burrow, feed and avoid crowding. A small tank with shallow bedding is far more likely to become cramped, even if the animal count seems low.
If you're still planning the enclosure, our Millipede Beginner & Buyer Guides and How to Start Keeping Millipedes are useful starting points.
Why there is no fixed stocking number
Millipedes are substrate-dependent animals. They burrow, rest, feed and often moult below the surface, so the usable habitat is the bedding rather than just the visible floor space. That is why there is no reliable universal number that works for every setup.
Two small millipedes in a compact enclosure may be too many, while a modest group in a large, well-established habitat may be fine. Species matters too: some stay relatively small, while larger adults need much more room once fully grown.
A good rule of thumb is that stocking becomes less about counting individuals and more about whether the enclosure has enough burrowing space, food material and shelter for the group you want to keep.
If you want to check the behaviour side of the question, see Can Millipedes Live Together?
Put the setup together
Think of the enclosure as a living woodland floor, not just a display tank. For a group setup, deep, loose substrate is more important than decoration.
Leaf litter, decaying wood and other natural organic material are part of the food base and shelter structure. The substrate should be deep enough for burrowing and stable enough that the lower layers stay usable over time. A few pieces of bark or moss on top will not make up for shallow bedding.
If you are unsure what enough space looks like in practical terms, What Size Enclosure Does a Millipede Need covers the enclosure-size side of the question, and How to Set Up a Millipede Enclosure explains the basics of building the habitat.
Check the conditions
Once the enclosure is running, the main question is whether it still has enough usable habitat for the group. A healthy millipede enclosure should smell earthy, not sour, and the substrate should stay moist and loose rather than compacting or drying out at the surface.
Watch how the animals use the enclosure rather than only how often you see them. Millipedes may spend long periods underground, and that is usually normal. What matters is whether the setup is being used without obvious signs of crowding.
Signs that the group may be too large for the setup include:
- leaf litter disappearing very quickly
- food material being consumed faster than you can replace it
- millipedes gathering in one damp area instead of spreading out
- reduced burrowing space because the substrate is too shallow or compacted
- foul or sour smells from wet, overloaded bedding
These signs do not always mean you need to split the group immediately, but they do show the enclosure is nearing its practical limit. In many cases, increasing substrate depth, floor space and organic material will help more than simply counting individuals.
What to adjust over time
Group size is not fixed forever. As millipedes grow and mature, the enclosure changes with them. What worked at the start may no longer be enough later on, especially if the substrate has settled or the animals have reached larger adult sizes.
The best time to adjust is before the enclosure becomes crowded. Add more leaf litter, replenish decaying wood where appropriate and keep the moisture balance stable so the lower substrate remains usable. If the group is clearly outgrowing the habitat, moving some animals to a second properly prepared enclosure can be the sensible option.
Avoid overmanaging a healthy setup. Frequent digging, full clean-outs and unnecessary rearranging can disturb the stable conditions millipedes depend on. A good enclosure usually improves slowly over time as the substrate becomes more biologically active.
So the right number of millipedes is the number your enclosure can support comfortably, with room for burrowing, food resources, shelter and stable moisture. Focus on the habitat first, then judge stocking from the space it provides.