The UK does not have the temperature extremes that some countries deal with, but it has enough seasonal variation to cause problems if you are keeping tropical invertebrates in a room with no climate control. A room that is 22C and comfortable in March can hit 30C in a July heatwave or drop to 14C in a January cold snap if the heating is off. Your animals feel every degree of that.
Winter
The heating problem
Central heating keeps your house warm but also dries the air out significantly. Radiators and forced-air heating reduce indoor humidity, sometimes to below 40%. For tropical invertebrates that need 60-80% humidity, this is a problem from October through to March.
You will need to mist more frequently in winter, even if your enclosures seemed fine in summer. Check substrate moisture levels regularly. The surface will dry faster in heated rooms than you expect. Sphagnum moss on top of the substrate helps buffer against rapid moisture loss.
Enclosures near radiators are the worst affected. The temperature gradient can also be extreme: one side of the tub baking at 28C while the other side sits at room temperature. Move enclosures away from direct heat sources. A shelf on an interior wall, away from windows and radiators, is more stable.
Temperature drops
If you heat your house consistently to 18-22C, most temperate and many tropical invertebrates will be fine through winter. The issue is when the heating goes off. A house that is 20C at bedtime can drop to 12-14C by morning in a poorly insulated room. Tropical species from equatorial regions (many isopod species, flower beetles, large millipedes) do not tolerate sustained temperatures below 16-18C.
If your house gets cold at night, consider a small heat mat on a thermostat for your tropical species. Place it on the side or underneath the enclosure (never on top, which dries the substrate out). Set the thermostat to maintain 20-22C. This is cheap to run and solves the nighttime temperature drop without heating the entire room.
Alternatively, keep your tropical enclosures in the warmest room of the house. This is often the living room or kitchen rather than a spare bedroom. A heated propagator or insulated shelf with a heat cable along the back is another option some keepers use for larger collections.
Reduced feeding
Many invertebrates eat less in winter, even when kept at stable temperatures. Shorter daylight hours and subtle temperature fluctuations can slow metabolism. Do not force-feed. Offer food as usual but do not panic if your spider goes a week without eating or your isopods seem less active at the food dish. Reduce the amount you offer slightly to avoid uneaten food sitting around and attracting grain mites.
Summer
Heat is the bigger danger
Most invertebrate deaths from temperature are not from cold. They are from heat. A room above 28C is uncomfortable for many species. Above 30C is dangerous. Above 33-34C is lethal for most tropical invertebrates, and it can happen faster than you think in a south-facing room with the sun streaming in.
Glass and plastic enclosures amplify the problem. A terrarium in direct sunlight acts like a greenhouse. Internal temperatures can exceed 40C even when the room temperature is a tolerable 26C. Keep enclosures out of direct sunlight at all times, but especially in summer. Even indirect sun through a window can warm a shelf significantly.
What to do during a heatwave
Move enclosures to the coolest room in the house. This is usually a north-facing room, the ground floor, or a room with stone or tile flooring that stays cooler. If your whole house is hot, close curtains during the day to reduce solar heating.
Increase misting frequency. Higher temperatures mean faster evaporation and lower relative humidity. What was adequate misting in spring is not enough in a 28C room. Mist more often but avoid waterlogging. You are replacing lost moisture, not turning the substrate into mud.
Some keepers place a frozen water bottle wrapped in a cloth near (not inside) the enclosure to create a local cool zone. This is a temporary measure for extreme heat, not a permanent solution. The bottle sweats and the effect only lasts a few hours, but it can buy time on the hottest days.
Do not add ice to the enclosure or mist with cold water. The sudden temperature change is a shock. Room-temperature water for misting is fine.
Ventilation adjustments
In summer, you may need more airflow than in winter. Stagnant hot air is worse than stagnant cool air. If your enclosures have minimal ventilation that was fine during cooler months, consider adding a few more ventilation holes or propping lids slightly for the summer period. Just be aware that increased ventilation means faster moisture loss, so adjust your misting schedule accordingly.
A small USB fan pointed at the shelf (not directly at the enclosures) can improve air circulation in a stuffy room. You want general air movement, not a direct wind blowing into the terrarium and drying everything out.
Pest season
Summer brings more pest issues. Fruit flies, fungus gnats, phorid flies, and grain mites all thrive in warm, humid conditions and breed faster when temperatures are up. Be extra diligent about removing uneaten food promptly in summer. What might sit safely for two days in a cool winter room will be swarming with flies within 24 hours in July.
Spring and autumn transitions
The trickiest times are the transitions. In spring, heating goes off but temperatures are not yet consistently warm. You get warm days followed by cold nights. The enclosure temperature swings more than in mid-winter (when the heating is reliably on) or mid-summer (when it is consistently warm). Monitor temperatures more closely during April-May and September-October.
Autumn is also when central heating comes back on, and the sudden drop in indoor humidity catches people off guard. If your isopod colony seemed fine all summer and starts struggling in October, check your humidity. The heating probably dried the air out more than you realised.
Invertebrate seasonal care in the UK is mostly about paying attention. The animals are not fussy if conditions stay within their tolerance range. But the UK climate means indoor conditions change significantly across the year, and your husbandry routine needs to change with them. What works in February will not work in July, and the other way round.