In their natural habitats, millipedes live in moist, dark environments like the leaf litter on forest floors. Many species sold as pet millipedes come from tropical habitats, and prefer warmer temperatures and higher humidity than other pet arthropods. Keeping environmental variables within the optimal range for your pet millipedes is important to their health and well being.
Millipedes require moisture in their environment, and prefer a slightly damp substrate. Use a mist bottle to add moisture to the tank daily, being careful not to wet the substrate too much. You can mist your pet millipedes, too!
Change the water on a daily basis, and change the substrate weekly. If you see fungus growing in the substrate, you are misting too much. If that happens, change the substrate completely, and mist less or improve air circulation in the terrarium.
African giant millipedes come from the tropics, and prefer a fairly warm environment of 75° to 85° Fahrenheit (24° to 29° Celsius). Most collected millipedes from temperate areas will require a temperature range between 60° and 78° Fahrenheit (16° to 26° Celsius).
If necessary, you can use a heat pad under the tank to keep the substrate warm. Keep in mind that this will dry out the substrate, so you will need to mist it much more frequently. Also watch your millipede's water bowl, as the water will evaporate quicker when a heat pad is used. Never use a heat lamp to warm your millipede terrarium. Millipedes do not like bright lights, and a heat lamp can dehydrate them quickly.
For more on keeping millipedes as pets, read my Guide to Caring for Pet Millipedes.