How Cold Is Too Cold for Isopods?

How cold is too cold for isopods? For most popular species, sustained temperatures below about 18°C (65°F) slow them down and stop breeding, while tropical species like Cubaris suffer below that and hardy temperate species such as Armadillidium vulgare can shrug off brief dips close to freezing. But the honest answer is "it depends on the species, and on how long" - a single cold night when the heating fails is very different from weeks of low temperatures. This guide breaks down the safe ranges species by species and what to do if your enclosure gets too cold.

Why Temperature Matters So Much for Isopods

Isopods are ectothermic: unlike you or me, they can't generate their own body heat, so they rely on the temperature of their surroundings and on behavioural thermoregulation - moving to warmer or cooler spots as needed. They're also one of the very few crustacean lineages to have made the permanent move from sea to land. In the oceans, temperatures are remarkably stable, so terrestrial isopods never evolved the machinery to regulate their own body heat or to ride out big extremes. That evolution from water to land explains a great deal about their modern temperature and humidity needs.

"Too Cold" Is About Duration as Much as Degrees

There's an important distinction to draw. Are we talking about one night when the heating failed, or about a room that sits cold for weeks? Those are very different things, and a colony that would happily survive the former might slowly decline under the latter.

Humidity complicates the picture too. Cold air holds less moisture than warm air, so even if the percentage on your hygrometer looks unchanged, a cold enclosure can effectively dry out - and getting moisture right matters as much as temperature, since the wrong levels invite mould, dehydration and stress. The ideal is always to mimic the microhabitat of your species' natural range. Looking up the temperatures in, say, Thailand is a start, but those aren't the temperatures a cave-mouth rainforest isopod actually experiences; many species do perfectly well when you focus on keeping isopods at room temperature with the right humidity and habitat.

How Isopods Keep Warm

Their main route to warmth is conduction - heat passing between their bodies and the surface they're resting on. With reptiles we tend to talk about infrared radiation and basking, but that relies on an animal sitting out in the open. Isopods spend most of their time tucked under cork bark or buried in leaf litter, so gentle, ambient warmth suits them far better than a basking lamp; our notes on isopod heating requirements cover safe options.

Air temperature still matters: if the air is too cold, an isopod loses heat faster than the substrate can replace it. When that happens they'll burrow down to conserve warmth, which is one reason a slightly moist, diggable substrate is so important - it lets them retreat and buffer themselves. If you do need to add heat, choosing the right method for heating an isopod enclosure makes keeping conditions stable much easier.

What the Research Tells Us

There's genuine science here, not just hobby lore. Studies on Porcellio scaber found that mancae (young isopods) grew more slowly at 15°C than at 22°C - but reached a larger adult size. The same body of work showed that at temperature extremes, isopods accumulated toxins such as heavy metals more readily, so an unsuitable temperature isn't only a metabolic issue, it can affect their resilience to other stressors too.

As temperatures drop, isopods also become measurably slower when moving - unsurprising, given their systems depend on external heat to keep ticking over. And one intriguing finding: isopods exposed to gently fluctuating temperatures proved more resilient than those held at a dead-constant temperature. The fluctuation was only a few degrees either way, but it suggests a slight natural dip at night does no harm at all - and may even be beneficial. References are listed at the end of this article.

Cold, Temperate and Tropical: a Useful but Imperfect Shorthand

Like many keeping hobbies, isopod care lumps species into cold, temperate and tropical. It's a handy shorthand, but worth a caveat: "temperate" and "tropical" describe places on Earth, not fixed temperatures. Peru sits squarely in the tropics, yet parts of it dip close to freezing at night for much of the year, while temperate Australia can get hotter than many tropical regions. In practice, isopod keepers mostly deal with tropical species (which want higher, more stable warmth) and temperate ones (which tolerate wider swings). The real lesson is to research the specific species you keep rather than trusting the label - especially when choosing the best isopods for a planted terrarium, where plants and invertebrates need to share the same conditions.

Temperature Ranges for Common Species

What a British room actually measures

Start with the number most care sheets leave out. They tell you room temperature is fine without ever saying what room temperature is, and the advice cannot be checked until somebody does. When BRE and DECC logged temperatures in 823 English homes over the year from February 2011 - still the largest measurement of its kind - the average across living room, hallway and main bedroom was 19.0°C through the heating season (October to April), 18.1°C in December, and 21.5°C across July and August. About two thirds kept the living room between 18 and 22°C in the heating season; roughly a quarter sat below 18°C. Energy has got a great deal more expensive since 2011, so if anything those figures are generous today.

Now put that beside the animals. Where isopods have been offered a thermal gradient, or had their performance optimum measured, the answers cluster tightly: 22-23°C for Armadillidium vulgare, 20.9°C for Porcellio scaber, 20.9-24.7°C across three populations of Porcellio laevis. Three species, studied decades apart by different groups, all landing in the low twenties.

So a British home in the heating season sits a degree or two below where these animals put themselves. That is the heating question in one sentence, and it explains why the advice you read contradicts itself. A temperate species at 19°C is comfortable and will live a long time; it will also breed slowly, because brood development in P. scaber runs to 59 days at 15°C against 23 days at 22°C. Survival and breeding are different questions, and "room temperature is fine" answers only the first.

The ceiling is real too. Taking P. scaber from 20°C to 28°C raised mortality two and a half times, from 9.4% to 23.4%. The same experiment left Mediterranean Porcellionides pruinosus untouched. Provenance beats any universal number, which is the honest reason the table below has such a wide spread: for a northern temperate species, heat to reach the low twenties rather than to pass through them; the Mediterranean Powders and the tropical species listed genuinely want more. One caution on the warm end - 22°C was the warmest condition anyone has tested for brood development, so there is no evidence that going hotter speeds breeding further, and good evidence it costs.

Most isopods thrive somewhere in the 20-27°C range, but tolerances vary widely. Below are sensible working figures for popular species - treat the "too cold" point as where problems begin, not as a target.

Tropical (heat-loving, cold-sensitive)

Cubaris species (Rubber Ducky, Panda King): a working 22-26°C; too cold below 18°C. Worth flagging that no thermal physiology has ever been published for Cubaris - that range is inferred from the limestone caves they come from, which sit at 23-25°C all year and close to saturated, not from the animals themselves. Stability matters more here than the number.
Porcellio magnificus / Porcellio expansus: optimal 22-27°C; too cold below 13°C.
Porcellio hoffmannseggii: optimal 24-29°C; too cold below 15°C.

Temperate (more adaptable, but prefer warmth)

Porcellionides pruinosus (Powder Blue, Powder Orange): optimal 21-27°C; can survive down to about 10°C.
Armadillidium vulgare (including Magic Potion): optimal 18-24°C; tolerates brief drops to around 4°C.
Porcellio scaber (Dalmatian, Orange Koi): optimal 18-24°C; can survive brief drops to around 2°C. A widespread, hardy detritivore and a popular clean-up crew that, unlike Armadillidium, can't roll into a ball.

Cold-tolerant (handle cooler conditions well)

Armadillidium nasatum: optimal 16-24°C; can survive around 2-4°C.
Armadillidium gestroi: optimal 18-24°C; too cold below 4°C.
Armadillidium klugii (Clown): optimal 18-24°C; tolerates down to around 4°C.

These are guidelines, not guarantees - a colony at the bottom of its range will slow right down and likely stop breeding even if it survives. For the species you keep, always check the specific care notes on the relevant product page.

How to Protect Isopods from the Cold

If your enclosure is unheated and the room gets cold

If you rely on room temperature and the heating fails, act as soon as you notice. Drape something insulating over the enclosure - a couple of towels work well - to trap any remaining warmth, taking care to leave the ventilation holes clear so airflow isn't cut off. If you have hot water to hand, fill a sealed container with it and tuck it under the towels to gently raise the temperature.

If your heated enclosure loses its heat source

The same insulation trick applies. If the house heating is still working, consider moving the enclosure to the warmest room - a bathroom or shower room is often a few degrees warmer than the rest of the house. Just make sure the isopods still have shaded spots to retreat to, so they're never forced to sit in warmth or light they can't escape.

In all cases, avoid the extremes at both ends. Keep enclosures out of draughts and well away from direct sunshine - extreme heat is every bit as dangerous as extreme cold. Aim to recreate what the species would experience in the wild, minus the extremes, and remember that a gentle night-time dip of a degree or two is natural and harmless. If cold has stalled your colony's breeding, our breeding troubleshooting guide covers how to get it going again once conditions are back to normal.

Frequently Asked Questions

Will my isopods die if the heating goes off for one night?
Usually not. Most species tolerate a single cold night, especially temperate ones - they'll slow down and breeding may pause, but they typically recover. Sustained cold is the real risk, so insulate the enclosure and restore warmth as soon as you can.

What's the coldest temperature isopods can survive?
It varies hugely by species. Hardy temperate species like Armadillidium vulgare and Porcellio scaber can endure brief drops to 2-4°C, whereas tropical Cubaris struggle below about 18°C.

Do isopods need a heat lamp?
No. Because they live under bark and leaf litter rather than basking, gentle ambient warmth (such as a low-wattage heat mat on the side of the enclosure) suits them far better than a basking lamp.

Is a constant temperature best?
Not necessarily. Research suggests isopods exposed to small natural fluctuations were more resilient than those kept at a constant temperature, so a slight night-time dip is fine. Browse our isopods for sale to find hardy species well suited to UK room temperatures.

And in 2026, the Opposite Problem

This guide is about cold, because that is the question British keepers have always asked. This summer it is the wrong question. 2026 is the first year in the UK record to reach 35°C in May, June and July, and the Met Office logged eight days above 34°C - beating the records set in 1976 and 2020. I have had customers lose colonies to heat this year, which is not something I used to hear.

Note what that does to the figure at the top of this page. The 21.5°C summer average comes from homes logged in 2011-12, and it is a two-month mean. A mean says nothing about the week inside it. The ceiling is the number that matters now: taking P. scaber from 20°C to 28°C raised mortality two and a half times. A south-facing room in a heatwave passes 28°C easily, and heat and dryness arrive together - an isopod in hot, dry air loses water fast, which is the actual mechanism behind most summer losses.

Our seasonal care guide covers the whole year across every group we sell. For the heat specifically, what helps, in the order I would do it:

Move the enclosure. A north-facing room, a ground floor, or a cool cupboard buys several degrees for nothing. Never a windowsill or a conservatory.
Go deeper, and mist more often. Deep substrate is a thermal refuge - the animals burrow down into cooler, damper ground and wait it out - and it is also a water reservoir, which is why a bigger box with more substrate and moss rides out a hot week better than a small one. Heat dries an enclosure fast, so in a hot spell you mist more often to hold the same moisture, not to make the tub wetter. Top up the damp end as it recedes rather than soaking the whole floor.
Move the air. I run variable-speed fans on the shelves, oscillating, with a mode that ramps the speed up and down rather than holding it constant, which is closer to how air actually moves outdoors. Watch the damp end while they run, because moving air carries moisture away - that trade-off is the whole trick.
Air conditioning, if you have it, is the only thing that reliably holds a room through a 35°C day. We use one - but be warned that an air conditioner is a dehumidifier that happens to cool. Mine is currently pulling sixteen to seventeen litres a day out of my invertebrate room, and that water comes out of the air, which takes it back from every damp surface it can reach. The fix for the heat creates the problem that actually kills them. Check your damp ends daily while it is running.
Do not open the tub to "let heat out". You lose the humidity and gain nothing; the substrate is the buffer.

One honest caveat: the Mediterranean species take this in their stride. The same experiment that saw P. scaber mortality climb left Porcellionides pruinosus - the Powders - untouched at 28°C. If you keep natives and temperate Armadillidium, they are the ones to worry about first.

References

Refinetti, R. (1984). "Behavioral Temperature Regulation in the Pill Bug, Armadillidium vulgare (Isopoda)." Crustaceana, 47(1), 29-43.

Abdel-Lateif, H. M., et al. (1998). "Interaction between Temperature and Cadmium Toxicity in the Isopod Porcellio scaber." Functional Ecology, 12(4), 521-527.

Castañeda, L. E., Lardies, M. A. & Bozinovic, F. (2004). Evolutionary Ecology Research, 6, thermal sensitivity of metabolic rate in three populations of Porcellio laevis.

Dailey, T. M., et al. (2009). "The Effects of Temperature, Desiccation, and Body Mass on the Locomotion of the Terrestrial Isopod Porcellio laevis." Comparative Biochemistry and Physiology Part A, 153(2), 162-166.

Römbke, T., Römbke, J. & Russell, D. (2011). "Effects of Temperature Increases on the Feeding Activity of Two Species of Isopods (Porcellio scaber, Porcellionides pruinosus) in Laboratory Tests." Soil Organisms, 83(2), 211-220.

Schuler, M. S., et al. (2011). "Isopods Failed to Acclimate Their Thermal Sensitivity of Locomotor Performance during Predictable or Stochastic Cooling." PLoS ONE, 6(6), e20905.

BRE / Department of Energy and Climate Change (2013). "Energy Follow-Up Survey 2011, Report 2: Mean Household Temperatures." Temperature logging in 823 English dwellings, February 2011 to January 2012.

Horváthová, T., et al. (2015). "Does Temperature and Oxygen Affect Duration of Intramarsupial Development and Juvenile Growth in the Terrestrial Isopod Porcellio scaber?" ZooKeys, 515, 67-79.

Antoł, A., Rojek, W., Singh, S., Piekarski, D. & Czarnoleski, M. (2019). "Hypoxia Causes Woodlice (Porcellio scaber) to Select Lower Temperatures and Impairs Their Thermal Performance and Heat Tolerance." PLoS ONE, 14(8), e0220647.