Seasonal Invertebrate Care Through a British Year

Quick answer: in a British house, heat is the dangerous end of the year and cold is the slow end. A cool winter room mostly makes invertebrates dormant and unproductive; a hot summer room kills them, and it kills them by drying them out as much as by cooking them. The most useful thing you can do in a heatwave is move the enclosure somewhere cooler and keep the damp end damp. And if you are running air conditioning to fix the heat, watch your enclosures closely, because the machine is pulling water out of the room faster than you would think.

Why a British year needs thinking about at all

Most care sheets give you one temperature range and leave it there, as though a room in January and the same room in August were the same place. They are not, and the gap has been measured. The largest measurement we have comes from 823 English homes logged across a full year in 2011-12 by BRE and DECC. Averaged over living room, hallway and main bedroom, those houses ran 19.0°C from October to April, bottomed out at 18.1°C in December, and reached 21.5°C over July and August. Winter living rooms clustered at 18 to 22°C for around two thirds of households, with roughly another quarter colder still.

That is a swing of three or four degrees across the year in the average of a whole house, and a far bigger one in any single room that catches sun. Set against animals that mostly want the low twenties, it means a British keeper spends half the year working up towards the target and half working down towards it. Those are different jobs and they need different kit.

British summers have also moved since that survey. The UK reached 35°C in May, June and July of 2026, which has never happened in one year before, and logged eight days above 34°C. I have had customers lose colonies to heat this year, which is new.

Heat is the dangerous end, and here is why

This is the thing I would most like keepers to take away, because it runs against the instinct that cold is what you protect animals from.

Cold has an exit. Heat does not. Every group in this shop has some documented, reversible way of sitting out conditions that are too cool. Springtails enter a chill coma somewhere between about 4 and 10°C depending on body size and how dry the air is, and walk it off again once things warm back through the low to mid teens. Millipedes have a real winter diapause, and in some species it will not break without a chilled period first. Isopods slow down, stop breeding and wait. None of that is good for productivity, but almost none of it is fatal at temperatures a British house reaches indoors.

There is no equivalent state above the optimum. Nothing in this catalogue can pause and sit out a heatwave, and the research says this is a general pattern and not bad luck: across a wide range of animals, heat tolerance is strikingly similar from species to species and place to place, while cold tolerance varies enormously and evolves far more readily. The warm side of the curve also narrows as an animal's optimum rises, so the warmer a species likes it, the smaller its margin before warm becomes too warm.

Heat also gets a second weapon. Warm air pulls water out of an animal faster, and the rate climbs steeply as temperature rises. So a hot enclosure attacks on two fronts at once, thermal stress and water loss, and for animals as leaky as these the water usually gets them first. That matches what I see. A colony lost in August is a dried-out colony far more often than a cooked one, and the older article on this site about what to do when it gets too hot reached the same conclusion from the other direction: the moisture drop worries me more than the temperature reading does.

The number that misleads everyone

You will find care sheets quoting impressive upper limits, figures up in the forties. Those come from ramping assays, where temperature is raised steadily and the animal is scored when it loses coordination, over minutes. They are not husbandry ceilings and they are wildly optimistic read as such.

The gap has been measured, and it is enormous. Blaptica dubia roaches have a critical thermal maximum somewhere around 45 to 50°C. Not one of them completes development to the fifth instar at a sustained 35°C. The temperature that stops a colony living is ten to fifteen degrees below the temperature that knocks an individual over in a lab. Chronic and acute are different questions and only one of them is about your shelf.

Summer: the part that actually costs people colonies

Cheapest and most effective first.

1. Move the enclosure. This is free and it beats everything else.

Room choice buys several degrees for nothing. A north-facing room, a ground floor, an interior cupboard, a garage that stays cool. Never a windowsill, never a conservatory, never a loft. What matters is not the air temperature on the weather app but the temperature inside the box, and a sealed tub in direct sun behaves like a greenhouse. Work on woodland millipedes made the point neatly: an exposed dry log in sunshine readily climbed past the temperature at which the animals living in it lose coordination.

2. Use a bigger enclosure than you think you need

I keep colonies in 11 litre boxes as a minimum, even for small counts, and heatwaves are a large part of why. A bigger box holds more substrate, more moss and more leaf litter, and that does three useful things at once.

• It holds more water. Damp substrate and moss are a reservoir. A small tub can go from correct to bone dry in a day of real heat, where a deep 11 litre box has enough water in it to ride out a missed maintenance day.
• It resists temperature change. Water takes a great deal of energy to warm, so a heavy damp substrate warms and cools more slowly than the air around it. That buffering is why depth is a refuge: the animals burrow down into ground that is measurably cooler and damper than the surface, and wait.
• It holds more food. More leaf litter and rotting wood means a colony that has not noticed you forgot a feed.

There is a related finding worth knowing. Woodlice lose water much more slowly in a crowd: isolated Porcellio scaber lost around 4.5% of body weight per hour in warm dry conditions, and in groups of forty or more that fell to under 2%, less than half, because huddling cuts the surface exposed to the air. A thin colony spread through a big box does not get that benefit. A healthy one does, and it is a good argument for not splitting groups down too far before a hot spell.

3. If you are running air conditioning, watch the moisture

This is the one that caught me out, and I have not seen it discussed anywhere else.

An air conditioner is a dehumidifier that happens to cool. It works by passing room air over a cold coil, and water condenses out onto that coil as it goes. In a heatwave the volume is startling. Mine is currently pulling sixteen to seventeen litres a day out of my invertebrate room. That water comes out of the air, and the air takes it straight back from every damp surface it can reach, which means every enclosure on the shelf.

So the fix for the heat quietly creates the problem that actually kills them. Cool a room with AC and change nothing else, and your enclosures will dry out faster than they ever do in winter while you congratulate yourself on having sorted the temperature.

Fans do the same damage by a different route. A fan removes no water from the room, but moving air strips away the saturated layer sitting right at the substrate surface and lets evaporation run much faster than it otherwise would. Different mechanism, same result on your damp end.

Neither is an argument against using them. It is an argument for checking the damp end every day while they run, instead of to your usual schedule.

4. Mist more often, to replace water rather than to cool

Extra misting in hot weather does help, and it is worth being precise about why, because the usual explanation is wrong.

Misting does not meaningfully cool the inside of an enclosure. Evaporative cooling only works when the air can accept more water vapour, and the air inside a humid invertebrate enclosure is already close to saturated. There is nowhere for the water to evaporate to, so there is almost no cooling available. I know of no measurement of misting lowering the temperature inside a vivarium, and the physics says the effect is close to nil.

What misting does is put back the water that heat, fans and air conditioning are taking out, and that is what saves colonies. In a hot week you are not misting to change the target, you are misting more often to hold it, because everything about a heatwave is working to dry the box out. Keep the gradient, one end damp and the far end drier, and top up the damp end as it recedes instead of soaking the whole floor. A hot waterlogged box has its own ways of going wrong.

One useful distinction: evaporative cooling does work on the outside of the box, because room air is nowhere near saturated. A damp towel laid over an enclosure will draw heat off as it dries, and a fan blowing across that towel helps. Water evaporating outside the box cools it; water misted inside the box does not.

5. Air conditioning, if you have it

It is the only thing that reliably holds a room through a 35°C day, and I run one. It is also the most expensive answer here, which is why it sits at the bottom rather than the top. Everything above it is cheaper and does most of the work. If you do use one, see point 3.

What not to do

Do not take the lid off to let the heat out. You lose the humidity, which is the thing keeping them alive, and gain very little temperature. The substrate is the buffer, not the air. And do not drop ice or a frozen bottle straight into an enclosure. You get condensation, a soaked patch and a sharp temperature swing, and swings are their own kind of stress.

Autumn: the shoulder, and the best working month of the year

Autumn is when British rooms drift back down through the low twenties, which is where most of this catalogue wants to be. It is the easiest season to keep things in and the best time for colony work, whether that is splitting, rehousing or starting new cultures, because you are not asking animals to establish while fighting the weather.

The thing to watch is the day the heating goes on. A room that has been drifting gently can jump several degrees, and it gets drier at the same time, because warming air without adding any water lowers the relative humidity. Check your damp ends in the week after the boiler starts up.

Winter: dormancy, not danger

In an average heated British home, winter is not a threat to most of what I sell. It is a productivity problem, and those are different things.

At around 19°C, temperate isopods live perfectly well and simply breed slowly. The clearest illustration is brood development in Porcellio scaber, which takes roughly 59 days at 15°C against 23 days at 22°C. Nothing is wrong with a colony that has stopped producing in January. It is doing what the temperature tells it to. Every winter I get messages from keepers convinced a colony has failed when it has only slowed down, and the answer is patience or a few degrees, not intervention.

If you do want winter production, gentle warmth into the low twenties is what delivers it. A low-wattage mat on a thermostat, against one side of the enclosure instead of underneath it, so the animals keep somewhere cooler to retreat to. Two cautions. First, heat to reach the low twenties, not to pass through them: move P. scaber from 20°C up to 28°C and mortality goes from 9.4% to 23.4%, two and a half times worse. Second, 22°C is the warmest temperature anyone has actually tested for brood development, so there is no evidence that going hotter speeds anything up further.

The genuine winter exceptions are the tropical species. Cave Cubaris, the large tropical millipedes and most display cockroaches do want supplementary heat through a British winter, and for them an unheated room is a real problem rather than a slow one. Worth knowing what "tropical" actually means for the cave species, though, because it is widely misread: the limestone caves these animals come from sit at 23 to 25°C all year and close to saturated, while the forest outside hits 29 to 30°C every afternoon. They are stable and wet, not hot. Reach for stability before you reach for heat.

Winter brings the same drying problem as summer from the opposite direction. Central heating lowers relative humidity, and an enclosure near a radiator will dry out steadily. It is a slower version of the August problem, and it catches people because they associate drying with heatwaves and not with January.

Spring

Things wake up. Breeding picks up as rooms warm, appetites return, and colonies that looked static through February start producing again. A good time to feed a little more heavily and to get rehousing done before summer. If you keep millipedes, this is when overwintered animals become active again.

How it differs by group

The isopod numbers above should not be assumed to carry across, and for several of these groups the honest answer is that nobody has measured it. Where that is the case I have said so.

Isopods

The best-studied group here by a distance. Offered a thermal gradient, or measured for the temperature at which they perform best, the answers cluster tightly in the low twenties: 22 to 23°C for Armadillidium vulgare, 20.9°C for Porcellio scaber, and 20.9 to 24.7°C across three populations of Porcellio laevis. Provenance matters more than any universal figure. The same experiment that saw P. scaber mortality climb at 28°C left Mediterranean Porcellionides pruinosus, the Powders, completely untouched. If you keep natives and temperate Armadillidium, those are the ones to worry about first in a heatwave. Nobody has published thermal physiology for Cubaris or Ardentiella at all, so anything said about the cave species is inference from cave measurements and not from the animals.

Millipedes

Mine dry out faster than my isopods do, and I treat them as the thirstier animal: deeper substrate, and a damp end I do not let recede. That is my experience and not a published comparison, and I would rather say so than dress it up, because the mechanism usually given for it does not survive checking. What is documented is that millipedes as a group are moisture-loving with poor ability to compensate once they start drying, that a burrowing non-feeding phase underground is a normal response to both drought and moulting, and that several species have a real winter diapause. There is no published preferred temperature for any of the big tropical species I sell. The 24 to 28°C you see quoted everywhere is a husbandry recommendation repeated in the literature, not a measurement. The African giant millipede guide covers the group in more detail.

Springtails

Better documented than anything here except isopods, because Folsomia candida is a standard soil-testing organism. The international test standard cultures it at 20 ± 2°C, which is about as close to an official correct temperature as this hobby gets, and a normal British room delivers it without help. Note that the numbers below are F. candida specifically. For the tropical whites, Thai reds, lilacs and the rest of the coloured species there is no published physiology, and I would treat warm-origin cultures as wanting a few degrees more.

They are extremely vulnerable to drying. An adult's cuticle is roughly ten to twenty times more permeable to water than a cockroach's, and the eggs show zero survival at 98.7% relative humidity and drier, which is effectively saturated. That is why a culture that looks fine can quietly stop producing after a dry spell: mild drought does not kill springtails, it stops them growing. Twenty days of moderately dry conditions killed none of them but left them with essentially no growth, while damp controls tripled in mass. In a heatwave, springtail cultures are the first thing I check.

Cockroaches

Blaptica dubia is the only hobby species with real published numbers and they are useful ones. Development completes at 20, 25 and 30°C, so an ordinary British room works, just slowly at the bottom of that. A sustained 35°C stops them completing development at all. For Panchlora nivea, Gyna, Eucorydia, Therea and Lucihormetica there is no published thermal or humidity physiology whatsoever, and anyone quoting precise figures for them is quoting somebody's care sheet.

One genuinely useful behavioural finding: hissing cockroaches huddle together significantly more when the air is dry. Clustering is a signal worth reading and not just a habit.

Land snails

Summer's distinctive failure here is aestivation, where the snail seals itself into its shell and shuts down. It is a normal evolved ability and not a disease, but it is worth knowing what brings it on, because the experimentally identified triggers read like a checklist of husbandry slips: unsuitable food, going without food, temperature and low humidity. Smaller snails start sooner than larger ones in identical conditions.

It is not free, either. A measured bout costs roughly half the snail's body weight, an 85% drop in heart rate and an 83% drop in oxygen consumption. A snail that seals up in a well-run enclosure is telling you something has slipped, and usually that something is moisture. Lab colonies of Lissachatina fulica do well at 21 to 25°C. For Subulina octona there is no published thermal data at all.

Beetles and larvae

Warmth drives development straightforwardly. Pachnoda iskuulka larvae reared at 24, 27 and 30°C took 101, 88 and 77 days from egg to adult. That is the only Pachnoda anyone has timed, and it is not the species I stock, so treat it as the shape of the relationship rather than a timetable. Beyond that the cupboard is bare: no published upper limit, no lower limit and no humidity tolerance for Pachnoda, Dicronorrhina or Phalacrognathus. Keep the substrate damp and the room in the twenties, and do not trust any precise figure you read for these, mine included.

What nobody knows yet

Worth stating plainly, because a lot of care content presents these as settled. There is no measured thermal preference for any hobby millipede, for any display cockroach other than Blaptica dubia, for either flower beetle genus, for Subulina octona, or for Cubaris and Ardentiella. Nobody has measured what misting does to the temperature inside a vivarium, and nobody has measured how fast a real enclosure dries out under a fan.

Where I have given numbers, they come from published work on the species named. Where I have given advice without numbers, it is what I do on my own shelves and I have tried to label it that way.

The short version, by season

• Summer is the dangerous one. Move the enclosure out of the sun, use a bigger box with deeper substrate, mist more often to replace what is lost, and if you run AC or fans, check the damp end daily.
• Autumn is the easy one and the best time for colony work. Watch the week the heating goes on.
• Winter is slow, not dangerous, for temperate species. Gentle heat into the low twenties if you want production. Tropical species do need it. Watch for radiator dryness.
• Spring wakes everything up. Feed a little more, and rehouse before summer.

For more detail, the isopod temperature guide covers the cold end species by species, the humidity guide explains why a moisture gradient needs a genuinely dry end to work at all, and the substrate guide covers building the deep water-holding base that does most of the buffering described here. New keepers should start with the beginner's guide. Everything you need for a setup is in the accessories range, and I am always happy to answer questions, so do get in touch.