How Big a Tub Do Isopods Need?

A starter culture of ten to twenty isopods will live perfectly well in a three litre tub. That surprises people who have come from keeping reptiles or fish, where stocking density is the whole conversation.

Isopods are not stocked by volume. The question that actually decides the size of the box is whether it can hold a moisture gradient, and a box that cannot is too small however few animals are in it.

The gradient is the real constraint

Nearly every isopod wants a choice: a damp end it can retreat to and a drier end it can sit in. That is not a refinement, it is the core of the husbandry, and it is how the animal regulates itself.

A tub that is too small is uniformly damp or uniformly dry. There is no distance across which the moisture can fall away, so the animal has nowhere to go and you have to get the single setting exactly right instead of letting it choose. That is why very small containers fail even at low numbers.

As a rule of thumb, you want enough length that one end can be visibly wet while the other is visibly dry. In practice that is somewhere around 20cm of floor at the very least, and more is easier.

Rough sizes by stage

• Starter culture, 10 to 20 animals: 3 litres is fine, and easier to keep stable than something larger.
• Established colony you are growing on: 6 to 9 litres. Room for a proper gradient and a deeper substrate.
• Production colony you are harvesting from: 9 litres and up, or several smaller tubs. Splitting a colony across two boxes is better insurance than one big one.
• Display setup: whatever looks right, provided it still holds a gradient and vents well.

Going bigger too early is a mild mistake rather than a serious one. A large tub with a small colony in it is harder to keep evenly damp and you will see the animals less, which is how people conclude a colony has crashed when it has simply spread out.

Depth matters more than footprint

If you have a choice between wider and deeper, choose deeper.

Isopods spend a great deal of their time under the surface, and that is where they moult, where mancae are safest, and where the moisture is stable. A shallow tray gives them nowhere to go. Aim for at least 5 to 8cm of substrate, more for burrowing species.

Depth also buys forgiveness. A deep substrate holds moisture through a missed misting in a way a thin layer never does.

You cannot really overcrowd them

Isopod colonies are self-limiting. They slow their own breeding as numbers rise rather than expanding until something collapses, so a crowded tub is not the emergency it would be with almost any other animal. There is more on that here.

What a crowded tub does do is exhaust the food and the leaf litter faster, and foul the substrate sooner. The answer is feeding and maintenance, or splitting the colony, rather than a bigger box.

Ventilation, which is where size and airflow meet

A bigger tub is easier to ventilate, and ventilation is where most colonies are actually lost. Still, humid air grows mould and stalls breeding faster than dry conditions do.

Whatever size you land on, put vents in it, and put them high on opposite sides so air crosses the enclosure rather than sitting in it. The drier Porcellio species need considerably more of this than most guides suggest.

It depends on the species, and here is how

Dry-loving species such as most Porcellio want more floor and much more airflow. They are the ones that punish a small, sealed box. Give them length so the dry end is genuinely dry.

Tropical species such as Cubaris want depth and stable humidity more than they want floor. A deeper, smaller box suits them better than a wide shallow one.

Small species such as dwarf whites will live in almost anything, which is why they are the standard cleanup crew for enclosures built around something else entirely.

Ready-made options are in enclosures, hides and setup, and a plain ventilated storage box does the job perfectly well if you would rather not buy one.

Frequently asked questions

How many isopods can I keep in a 3 litre tub?

A starter culture of 10 to 20 will be comfortable and will breed. The colony will find its own ceiling well before the tub becomes a problem, but expect to split or upsize as it grows.

Is a bigger tub always better?

No. A large box with a small colony is harder to keep evenly damp and makes the animals much harder to see, which worries people unnecessarily. Match the box to the colony and move up as it grows.

How deep should the substrate be?

5 to 8cm as a minimum, and more for species that burrow. Depth holds moisture and gives mancae somewhere safe, so it does more for you than extra floor space does.

Can I keep isopods in a glass tank?

Yes, provided it is well ventilated. Glass tanks are usually designed to hold heat and humidity in, so they need more attention to airflow than a vented plastic tub does.

Do I need a lid?

Yes, both to hold humidity and to keep the colony in. Most isopods climb better than people expect, and some species climb very well indeed.