You've picked your species. Now you need somewhere to put it. Getting the enclosure right before the animal arrives is the single most useful thing you can do as a new keeper. An enclosure that's already at the right temperature and humidity gives your animal the best possible start. Scrambling to fix conditions with a stressed animal inside is no fun for either of you.
Choosing a container
You don't need anything fancy. The three main options are:
- Plastic tubs with modified lids (cheap, hold humidity well, easy to stack)
- Glass terrariums with front-opening doors (look nice, heavier, lose humidity faster)
- Acrylic enclosures (lightweight, clear, good for display species like jumping spiders)
Plastic tubs are the workhorses of the hobby. Most isopod, millipede, and beetle keepers use them. Drill or melt ventilation holes in the lid and upper sides. The holes need to be smaller than the animals, obviously. For isopods and small beetles, a fine mesh glued over larger holes works well.
For species that need more height, like mantids or arboreal spiders, glass or acrylic enclosures with mesh tops are better. Mantids in particular need to hang upside-down to molt safely, so the enclosure must be at least three times the animal's length in height, with a mesh or textured ceiling they can grip.
Ventilation
Airflow prevents mould and bacterial problems. But too much ventilation in a humid enclosure just dries it out. You're balancing two things: enough air movement to stop conditions going stagnant, and enough moisture retention to keep humidity where your species needs it.
For tropical species that need 70%+ humidity (many isopods, millipedes), use fewer, smaller ventilation holes. For species that need drier conditions with good airflow (jumping spiders), use more holes or mesh panels on opposite sides for cross-ventilation. You can always add more holes later if conditions are too damp. You can't easily take them away.
Substrate
This is where most beginners go wrong, and it's where most animals die. Substrate isn't just bedding. For many invertebrates, it's their food source, their home, their moulting chamber, and their nursery.
For isopods
Mix organic topsoil (no fertilisers or pesticides) with sphagnum moss and leaf litter. Oak and beech leaves are standard. Add a calcium source: cuttlebone, crushed eggshell, or limestone. Depth should be enough for females to retreat below the surface for brooding. About 5-8cm works for most species.
For millipedes
Similar to isopods but deeper: 10-15cm minimum for large species like Archispirostreptus gigas. Mix organic topsoil with rotting hardwood (oak, beech, birch), leaf litter, and sphagnum moss. Add calcium. Millipedes eat the decaying wood and leaves, so this isn't just substrate, it's food. All wood must be hardwood. Softwoods (pine, cedar, spruce) contain phenols that are toxic. Commercially treated wood is also dangerous.
For beetle larvae
Fermented hardwood flake soil. Full stop. Flower beetle larvae (Pachnoda, Mecynorrhina) and rhinoceros beetle larvae eat this material. Regular potting soil, garden compost, or unfermented wood shavings will not sustain them. They'll appear to eat it but won't get the nutrition they need, and they'll die over a period of weeks. Buy proper flake soil from an invert supplier.
Substrate depth for larvae should be proportional to their size. Deeper is better. Gently compress the substrate when setting up, because larvae need firm enough material to build stable pupal cells when they're ready to pupate.
For jumping spiders
Much less critical. A thin layer of coco fibre, sphagnum moss, or even paper towel works. The spider spends most of its time off the ground. The substrate just needs to hold a bit of moisture for humidity and look tidy if you care about that.
Heating
If your house stays above 20C year-round, many tropical species will be fine without supplemental heat. Most British houses don't, especially overnight in winter.
Heat mats are the standard solution for invertebrates. Stick them to the side or underneath the enclosure (never inside it). Always use a thermostat. An unregulated heat mat can overheat and kill everything in the enclosure. Set the thermostat to the species' preferred range and check with a thermometer that the actual temperature inside the enclosure matches.
Avoid heat lamps for most invertebrates. Overhead heat dries out the enclosure and can desiccate animals that need humidity. Side-mounted or under-tank heat mats with thermostats give you warmth without destroying your humidity.
Humidity
A spray bottle and a cheap digital hygrometer are your best friends. Analog hygrometers (the round dial type often sold with terrariums) are consistently inaccurate by 10-20%. Spend a few quid on a digital one.
Most tropical invertebrates do well between 60-80% humidity, but species-specific needs vary. The goal for many setups is a moisture gradient: one side of the enclosure damper than the other, so the animals can move to where they're comfortable. Spray the damp end, leave the dry end alone.
Use dechlorinated or aged water. Tap water with chlorine or chloramine can harm invertebrates over time, particularly isopods, which breathe through gill-like pleopods and are directly exposed to water quality.
Decor and hides
Most invertebrates need somewhere to hide. Cork bark is the universal go-to: it's lightweight, rot-resistant, and holds moisture. Pieces of bark, leaf litter, sphagnum moss clumps, and small branches all give animals places to retreat, climb, and feel secure.
For arboreal species (mantids, jumping spiders), add vertical climbing surfaces: twigs, cork bark pieces stood on end, or fake plants for grip.
Before the animal goes in
Set the enclosure up at least 24 hours before introducing your animal. This gives you time to check that:
- Temperature is stable and in the right range
- Humidity is holding where you want it
- Ventilation is adequate (no condensation covering every surface, but substrate isn't drying out within hours)
- There are no sharp edges, gaps, or exposed heat sources that could injure the animal
It's much easier to adjust a dry enclosure than to rescue a dehydrated animal. Get it right first, then add the occupant.